Thermoelectric Materials: A Scientometric Analysis of Recent Advancements and Future Research Directions

Abstract

This scientometric study looks at the current trend in thermoelectric materials research and explores the evolving domain of thermoelectric materials research using a combination of bibliometric and scientometric methodologies. The analysis examines global research trends from a dataset of over 37,739 research articles, focusing on thematic evolution, annual growth rates, and significant contributions. Six principal research clusters were identified, encompassing energy conversion, material synthesis and nanostructures (the most prominent cluster), computational modeling and material properties, measurement and characterization, material performance enhancement, and material processing and microstructure. Each cluster highlights a critical aspect of the field, reflecting its broad scope and depth. The key findings reveal a marked annual increase in research output, highlighting the growing global importance of thermoelectric materials in sustainable energy solutions. This is especially evident in the significant contributions from China and the USA, emphasizing their leadership in the field. The study also highlights the collaborative nature of thermoelectric research, showing the impact of global partnerships and the synergistic effects of international collaboration in advancing the field. Overall, this analysis provides a comprehensive overview of the thermoelectric materials research landscape over the past decade, offering insights into trends, geographic contributions, collaborative networks, and research growth. The findings underscore thermoelectric materials’ vital role in addressing global energy challenges, highlighting recent advancements and industrial applications for energy efficiency and sustainability.

1. Introduction

In the contemporary energy technology landscape, thermoelectric materials are pivotal solutions to some of the most pressing challenges [1,2]. These materials, which can directly convert heat into electricity and vice versa, stand at the forefront of sustainable energy research [3]. In an era increasingly defined by the need for renewable energy sources and efficient energy utilization, thermoelectric materials offer a promising pathway to harnessing waste heat and other thermal sources otherwise lost in industrial processes and everyday applications [4]. Their potential to provide a cleaner, more efficient means of energy conversion is not just a scientific interest but a necessity to sustainably meet the growing global energy demands [4]. This increasing urgency for environmentally friendly and energy-efficient technologies has spurred significant advancements in thermoelectrics, driving research and innovation toward materials that can operate with higher performance and at a lower ecological cost.

The development of thermoelectric materials, pivotal in energy conversion, began in the early 19th century with the discovery of the Seebeck effect by Thomas Johann Seebeck in 1821 [5]. This phenomenon, where a temperature difference in a conductor generates voltage, laid the foundation for thermoelectric energy conversion [2]. In 1834, Jean Charles Athanase Peltier discovered the Peltier effect, revealing that electric current through different conductors can absorb or create heat, essential for thermoelectric cooling. A huge advancement occurred in the mid-20th century with the development of semiconductor-based thermoelectric materials, notably bismuth telluride. This marked a turning point, enhancing the efficiency and practicality of these materials in various applications. These milestones have been crucial in the evolution of thermoelectric materials, shaping their modern application in sustainable energy technologies.

Thermoelectric devices operate on the Seebeck, Peltier, and Thomson effects [6]. The Seebeck effect generates electricity from a temperature difference across dissimilar materials, which is essential in thermoelectric generators for converting waste heat into power [7]. The Peltier effect, where passing an electric current through two different materials causes heat absorption or release, is utilized in thermoelectric coolers for temperature control [8]. Lastly, the Thomson effect, involving heat generation or absorption in a material under a temperature gradient with an electric current, enhances device efficiency [7]. These principles are integrated into thermoelectric modules for energy harvesting and cooling applications, demonstrating thermoelectric technology’s versatility and efficiency [7,8,9].

Current research in thermoelectric materials is characterized by innovative trends aimed at enhancing their efficiency and applicability. A significant focus of this research is nanostructuring, where materials are engineered at the nanoscale to improve their thermoelectric performance [5,10,11,12]. Nanostructuring has proven effective in reducing thermal conductivity without compromising electrical conductivity, a critical balance for achieving high thermoelectric efficiency [13]. This approach leverages the unique properties of materials at the nanoscale to optimize performance, particularly in terms of the dimensionless figure of merit (ZT) [13]. In addition to nanostructuring, band structure optimization has also emerged as an important strategy for enhancing thermoelectric properties. By engineering the electronic band structure, researchers can manipulate key parameters such as the Seebeck coefficient and electrical conductivity, improving the efficiency of thermoelectric materials. Recent studies have demonstrated the effectiveness of this approach, showing significant performance improvements through band structure optimization [14,15,16,17,18,19,20]. Band structure optimization works in tandem with nanostructuring to target both the electronic and thermal properties of materials, offering a comprehensive path toward optimizing the ZT value.

Recently, environmentally sustainable magnesium-based thermoelectric materials have attracted significant attention in green refrigeration technology due to their abundance, cost-effectiveness, and non-toxicity. These materials, alongside advancements in both nanostructuring and band structure regulation, represent the forefront of efforts to achieve higher thermoelectric efficiency and broader applicability. Magnesium-based thermoelectric materials are low-cost materials with high-energy conversion efficiency and excellent thermoelectric optimization performance due to a multivalley conduction band near the Fermi level. Moreover, excess magnesium in prepared thermoelectric samples improves performance by forming interstitials. Magnesium stannides, among magnesium-based thermoelectric materials, have gathered significant attention due to their ease of tuning thermoelectric figures of merit and adjustable power factor. The power factor, determined by the square of the Seebeck coefficient and electrical conductivity, plays a crucial role in enhancing the thermoelectric figure of merit, necessitating an increase in power factor and a reduction in lattice thermal conductivity.

Strategies for identifying high figure-of-merit thermoelectric materials involve incorporating extrinsic features into existing ones and searching for pristine materials with intrinsic transportation mechanisms. Artificial intelligence is gaining wide acceptance for modeling and designing magnesium-based thermoelectric materials with desired energy conversion efficiency [13]. Furthermore, the thermoelectric figure of merit (TFM) of magnesium-based thermoelectric materials was modeled using advanced computational intelligence algorithms such as extreme learning machines (ELM) and support vector regression (GSVR). The research focuses on enhancing the energy conversion efficiency of magnesium-based thermoelectric materials, crucial for sustainable technologies like green refrigeration and waste heat recovery [21]. In another study, the thermoelectric figure of merit of doped BiCuSeO thermoelectric material was modeled using a genetically hybridized support vector regression (HSVR) computational method [22].

Another notable trend is the development of composite materials. By combining different materials, researchers aim to create composites that synergize the best properties of each component [7,9,23,24]. These composite materials often exhibit improved thermoelectric performance due to reduced thermal conductivity and enhanced power factor, a product of electrical conductivity and the Seebeck coefficient [25]. The optimization of material properties remains a central theme in current research. Efforts are concentrated on enhancing electrical conductivity and the Seebeck coefficient while minimizing thermal conductivity [26,27]. This optimization is crucial for developing more efficient thermoelectric materials that convert heat into electricity.

There is a growing interest in developing environmentally friendly and abundantly available thermoelectric materials, driven by the need for sustainable solutions that not only enhance efficiency but also minimize environmental impact [28,29,30]. Current trends reflect a dynamic field that integrates material science, nanotechnology, and environmental considerations, aiming to unlock the full potential of thermoelectric materials in energy conversion applications.

In the rapidly evolving field of thermoelectric materials research, scientometric analysis offers critical insights beyond traditional technical qualitative research. This study aims to provide a comprehensive scientometric overview from 2014 to 2023, analyzing 37,739 documents and over 600,000 citations to understand the field’s growth and evolving interests. The scientometric analysis provides a panoramic view of the scientific landscape, showing more than numerical growth. It delves into the qualitative dimensions of research trends, thematic evolutions, and collaborative networks. This analysis not only helps understand the current state of research but also aids in predicting future directions and potential breakthroughs [31,32,33].

A significant component of this study is the analysis of citation patterns, which offers insights into the impact and influence of specific studies. High citation counts indicate key milestones in thermoelectric research, marking the community’s recognition of groundbreaking work. Furthermore, the analysis sheds light on the collaborative nature of the field, revealing an intricate network of collaborations among researchers, institutions, and countries. This aspect underscores the importance of collective, interdisciplinary efforts in driving scientific progress. This scientometric analysis uncovers a rich and multifaceted thermoelectric materials research narrative characterized by rapid growth, evolving focuses, impactful contributions and extensive collaborations. The insights gained are invaluable for researchers, policymakers, and stakeholders, guiding future efforts and investments in this critical domain of materials science and providing valuable insights into its current state and future directions.

This paper is structured as follows: Section 2 details the methodology of the scientometric analysis, explaining the data collection process and the analytical techniques for examining thermoelectric materials research from 2014 to 2023. It covers quantitative and qualitative methods, including publication counts, citation metrics, and thematic analysis. Section 3 presents the results, delving into the trends in publication volumes, shifts in research focus based on keyword analysis, significant papers and authors, and collaborative networks within the thermoelectric research community. The paper concludes in Section 4, where we synthesize the findings and discuss their implications for the future of thermoelectric materials research. Section 5 emphasizes the importance of the study in shaping research directions and informing policy and funding decisions in this evolving field.

2. Working Principle of Thermoelectric Materials

The fundamental operation of thermoelectric materials is based on the Seebeck and Peltier effects. These effects exploit the properties of semiconductors to convert thermal energy into electrical energy and vice versa. Following is a brief description of these principles:

When a temperature differential is established between two ends of a thermoelectric material, as depicted in Figure 1, charge carriers in the form of electrons in n-type materials or holes in p-type materials diffuse from the hot side to the cold side. This creates a voltage difference across the material due to the different potentials, which can drive a current through an external circuit. The Seebeck effect is the basis for thermoelectric generators (TEGs), which convert waste heat into usable electrical power [34]. The Peltier module operates based on the Peltier effect, which occurs when a voltage is applied across two distinct conductor terminals linked by a semiconductor material [35]. These result in a thermal disparity, causing heat to be transferred from the hot side to the cold side, as illustrated in Figure 1. The current flow across the junction can either absorb heat from or release heat into the surroundings, depending on the direction of the current. When electrical energy is supplied to the module, the positive and negative charge carriers engage in energy exchange [36]. This energy exchange manifests as one side of the module absorbing thermal energy and transporting it to the opposite side [37]. If the polarity of the electrical input is reversed, the sides designated as hot and cold will also switch, demonstrating the reversible nature of the thermal effects produced by the module [38].

2.1. Recent Trends in Thermoelectric Materials Research

Recent research on thermoelectric materials has demonstrated remarkable advancements in optimizing thermoelectric efficiency through a blend of innovative material designs and cutting-edge nanostructuring techniques. By targeting reductions in lattice thermal conductivity and simultaneously enhancing electrical conductivity and Seebeck coefficients, researchers have achieved notable improvements in the figure of merit (ZT). For instance, Ghannam et al. conducted an important study exploring the thermoelectric properties of nanostructured α-SrSi₂, a material with potential for room-temperature thermoelectric applications. The research employed ball milling and spark plasma sintering techniques to significantly reduce the lattice thermal conductivity of α-SrSi₂ by producing nanostructured pellets with grain sizes around 200 nm. This resulted in an improvement in the material’s thermoelectric figure of merit (ZT) to 0.20 at room temperature. Additionally, the study demonstrated the influence of the elemental purity of Sr on the thermoelectric performance, emphasizing the critical role of controlling impurity levels. These findings make α-SrSi₂ a promising candidate for thermoelectric applications, although it remains less efficient compared to commercially competitive materials like Bi₂Te₃ [40,41]. Zhou et al. explored single-crystal thermoelectric materials with reduced thermal conductivity, showcasing significant potential for high-performance applications [42]. Additionally, hybrid approaches incorporating carbon nanomaterials and polymer composites have been successfully employed to boost both thermoelectric performance and scalability, driving forward the next generation of materials suited for power generation and cooling in renewable energy systems [43]. These breakthroughs are paving the way for more efficient, cost-effective solutions, positioning thermoelectric technology as a crucial factor in the future of sustainable energy.

However, despite these advancements, significant challenges remain in the field. One of the primary limitations lies in achieving high thermoelectric efficiency at room temperature, a critical requirement for widespread applications. Materials such as Bi₂Te₃ continue to outperform many new developments, creating a performance gap that needs to be addressed. Scalability is another persistent issue, as nanostructured materials, though effective in reducing thermal conductivity, are difficult and expensive to produce on a large scale [44]. Furthermore, many studies have focused primarily on short-term performance, leaving the long-term stability and durability of these materials underexplored, particularly in fluctuating thermal environments, which is crucial for real-world applications in industrial and consumer devices.

Looking ahead, future research must prioritize both performance enhancement and practical scalability. The development of hybrid materials that combine organic and inorganic elements is a promising avenue for balancing performance with cost-effectiveness. Machine learning- and AI-driven materials discovery could accelerate the identification of new thermoelectric compounds with superior properties, leading to faster optimization of the Seebeck coefficient and other critical metrics [45]. Additionally, enhancing the mechanical and thermal stability of thermoelectric devices through innovative coatings and structural improvements will be essential for long-term application, especially in large-scale renewable energy systems [46]. Exploring more environmentally friendly materials, such as silicides and oxides, could also provide sustainable alternatives to current materials, pushing thermoelectric technologies toward greater sustainability.

2.2. Industrial Applications of Thermoelectric Materials: Bridging Research and Practice

While much of the current research on thermoelectric materials has focused on academic outputs, recent years have seen significant strides in translating these findings into industrial applications. One prominent example is the integration of thermoelectric generators (TEGs) into waste heat recovery systems [47]. These systems are now being employed in industries such as automotive manufacturing and heavy industry, where they capture and convert waste heat into usable electrical power, contributing to enhanced energy efficiency and reduced environmental impact [48].

Another important application of thermoelectric materials is in green refrigeration technologies, particularly with the use of magnesium-based thermoelectric materials [49,50]. These materials are gaining attention due to their abundance, non-toxic nature, and cost-effectiveness. They have to be valuable in providing sustainable refrigeration solutions that align with the global push towards environmentally friendly technologies [50]. These examples underscore the transition from academic research to practical, real-world applications. As industries continue to seek innovative solutions for energy efficiency and sustainability, the potential for thermoelectric materials in various sectors, including automotive, HVAC, and renewable energy, is expected to grow [51].

2.3. Technological Limitations of Thermoelectric Materials

Despite the impressive advancements in thermoelectric materials, their current technological limitations emanating from limited operating temperature ranges, environmental concerns, high costs, material property trade-offs, and stability issues continue to impede their widespread application. These technological limitations are further discussed as follows.

• Interdependent Material Properties: The efficiency of thermoelectric materials is governed by the dimensionless figure of merit (ZT), which is highly dependent on the Seebeck coefficient, electrical conductivity, and thermal conductivity. However, these parameters are interdependent: improving one often negatively influences another. For instance, enhancing electrical conductivity can inadvertently increase thermal conductivity, thereby reducing overall efficiency [52]. Developing high-performance materials that balance these properties remains a major challenge.
• Limited Temperature Range: Thermoelectric materials perform optimally in specific temperature ranges, which limits their practical application. High-efficiency thermoelectric materials, such as bismuth telluride, are effective only at low temperatures, while materials designed for higher temperatures, such as half-Heusler alloys, face performance degradation and instability over time. This narrow operating temperature range poses a significant barrier to the implementation of thermoelectric materials in industrial settings [53,54].
• Thermal Conductivity Control: One of the most critical aspects of improving thermoelectric efficiency is reducing thermal conductivity without adversely affecting electrical conductivity. Recent advancements, such as nanostructuring and low-dimensional systems, have significantly reduced lattice thermal conductivity, but achieving consistent and scalable production remains a challenge [54]. Moreover, controlling thermal conductivity on a large scale without compromising mechanical stability remains difficult.
• Environmental and Resource Concerns: Many high-performance thermoelectric materials, including those based on tellurium, bismuth, and lead, pose environmental and resource sustainability issues. These materials are often rare, expensive, or toxic, raising concerns about their long-term feasibility for large-scale industrial use. Consequently, there is a growing demand for earth-abundant, non-toxic materials, though their performance still lags behind the best conventional thermoelectric materials [55].
• High Production Costs: The complex fabrication processes required for high-performance thermoelectric materials contribute to their high costs, making them economically unfeasible for widespread use. Techniques such as nanostructuring and advanced doping strategies are difficult to scale, leading to increased manufacturing costs. Furthermore, these materials often require rare or expensive elements, further limiting their commercial potential [56].
• Mechanical and Chemical Stability: Thermoelectric materials, especially nanostructured and low-dimensional materials, often face challenges related to long-term mechanical and chemical stability. Under prolonged use, these materials can degrade due to thermal cycling, leading to a reduction in their efficiency and lifespan [57].

3. Methodology

Bibliometrics, the core methodological approach for this investigation, adopts a quantitative approach, leveraging statistical methods to review and appraise the academic literature systematically [58]. This study delves into a subset of bibliometrics, namely scientometrics, which specifically targets the analysis of scientific texts [59,60]. The bibliometric technique, also known as science mapping, was applied to scrutinize various aspects of scholarly productivity in thermoelectric research. This technique facilitates visualizing connections between disciplines, sectors, specialties, documents, and authors. It encompasses a broad spectrum of bibliometric indicators, such as growth in the literature over time, contributions by leading countries and institutions, prolific authors, essential sources, author keywords, collaboration patterns among nations, funding bodies, top-cited papers, and thematic research trends. To collect relevant bibliographic data, a precise search string was formulated and entered into the advanced search feature of the Web of Science database, focusing on the term TS = (“Thermoelectric materials” OR “Thermoelectric”). The search was conducted on 23 November 2023, at the University of Hafr Al Batin, Saudi Arabia, yielding 64,831 papers. From the initial pool of 64,831 documents, a set of exclusion and inclusion criteria was applied, resulting in the elimination of 857 publications by excluding document types, namely dance performance reviews; biographical items; abstracts of published items; retractions or corrections; additions, reprints, or retracted publications; data papers; news items; or early access. This study concentrated solely on research articles, reviews, proceedings papers, book chapters, book reviews, etc., about thermoelectric materials. Papers not written in English were also excluded, resulting in a total of 1648 being excluded from the 63,974 publications, which included 62,326 papers in English language. Furthermore, the study only included publication years from 2014 to 2023, excluding 24,587 publications, and finally included 37,739 publications for the analysis. The chosen 37,739 research papers were downloaded in different formats like plaintext and tab-delimited files. These were subsequently examined using various bibliometric tools such as VOSviewer, version 1.6.19 [61], Biblioshiny—SSSM 2023 [62], Histcite—HistCite Pro™, Bibexcel-version 1.0.3. pip, and Microsoft Excel-2016. Figure 2 visually depicts the entire methodology used for data collection in this analysis.

4. Results and Discussion

4.1. Yearly Publications and Citations Trends

Figure 3 illustrates the trends in yearly publications on thermoelectric materials from 2014 to 2023, showing a generally upward trajectory in research, reflecting a growing interest in this field—the data peak in 2021 with 4978 publications, indicating a significant surge in research activities. However, there is a noticeable decline in the subsequent two years, which could be attributed to factors such as research saturation, shifts in funding, or global economic and political changes. The steady increase in publications up to 2020 emphasizes the expanding role and potential of thermoelectric materials in various applications. The consistently high volume of research throughout these years highlights the significance of this field, likely propelled by its applications in energy conversion and efficiency. This evolving trend, influenced by various external factors, delineates the dynamic nature of research in thermoelectric materials.

4.2. Document Type

Figure 4 presents the distribution of scholarly documents in thermoelectric materials research. The chart is dominated by articles, with 31,845 records, indicating a primary focus on publishing original research. Following this is proceedings papers, amounting to 2996 records, highlighting the significant role of conferences in disseminating research findings. Reviews, with 1629 records, play an essential part in compiling and evaluating existing research. Combined categories like articles and proceedings papers are also present, though less frequently. Editorial materials and meeting abstracts, although less numerous, represent a variety of scholarly communication formats. Less common document types, such as reviews with book chapters and letters, occupy more specialized roles within the academic discourse. Overall, the field is characterized by a pronounced emphasis on primary research articles and an active participation in conferences, supported by various other scholarly contributions.

4.3. Top Leading Journals in Thermoelectric Materials Research

Table 1. Top 20 high-yield sources on thermoelectric materials. Data from Web of Science (https://www.webofscience.com/wos/woscc/summary/8dc0bf2b-8a02-492e-9254-e6aac492a1ba-010e6befe7/relevance/1) (accessed on 23 November 2023) based on 37,739 publications.

Rank	Publication Titles	Record Count	% of 37,739	Total Citation (TC)	Total Citation/ Total Paper (TC/TP)	Journal Impact Factor	Country
1	Journal of Alloys and Compounds	1216	3.222	16,812	13.83	6.20	Switzerland
2	Journal of Electronic Materials	1147	3.039	11,173	9.74	2.10	USA
3	Physical Review B	939	2.488	20,766	22.12	3.70	USA
4	ACS Applied Materials Interfaces	728	1.929	16,669	22.90	9.50	USA
5	Journal of Applied Physics	680	1.802	9440	13.88	3.20	USA
6	Applied Physics Letters	613	1.624	10,707	17.47	4.00	USA
7	Journal of Materials Chemistry A	597	1.582	21,048	35.26	11.90	England
8	Energy Conversion and Management	444	1.177	15,661	35.27	10.40	England
9	Physical Chemistry Chemical Physics	444	1.177	9233	20.80	3.30	England
10	Journal OF Materials Chemistry C	409	1.084	11,735	28.69	6.40	England
11	RSC Advances	409	1.084	8551	20.91	3.90	England
12	Ceramics International	399	1.057	4087	10.24	5.20	England
13	Energy	392	1.039	10,608	27.06	8.90	England
14	Applied Thermal Engineering	387	1.025	8305	21.46	6.40	England
15	Chemistry of Materials	366	0.97	13,371	36.53	8.60	USA
16	Scientific Reports	360	0.954	10,015	27.82	4.60	England
17	ACS Applied Energy Materials	356	0.943	4309	12.10	6.40	England
18	Nano Energy	327	0.866	14,230	43.52	17.60	USA
19	Journal of Materials Science Materials in Electronics	315	0.835	2101	6.67	2.80	USA
20	AIP Conference Proceedings	299	0.792	513	1.72	0.41	USA

highlights the leading sources in thermoelectric materials research, showcasing the top 20 journals and publications. The “Journal of Alloys and Compounds”, “Journal of Electronic Materials”, and “Physical Review B” emerge as frontrunners in terms of record count, indicating their pivotal role in disseminating research in this field. These journals, predominantly based in the USA and England, reflect the wide-ranging interest across various scientific disciplines. Notably, publications like “ACS Applied Materials Interfaces” and “Journal of Materials Chemistry A” are distinguished by their high citations per paper and impact factors, underscoring the significant influence of their published papers. While “AIP Conference Proceedings” predominantly covers conference papers and tends to have lower citation numbers, “Nano Energy” has a high impact factor of 17.60, highlighting its importance in the field. Overall, the data from this table demonstrate the diverse and impactful nature of thermoelectric materials research, with a concentration of influential work in specific countries and journals.

4.4. Top Leading Authors

Table 2. Top 20 high-yield authors on thermoelectric materials. Data from Web of Science (https://www.webofscience.com/wos/woscc/summary/8dc0bf2b-8a02-492e-9254-e6aac492a1ba-010e6befe7/relevance/1) (accessed on 23 November 2023) based on 37,739 publications.

Rank	Authors	Affiliations	Country	Record Count	% of 37,739	Total Citations (TC)	Total Citations/Total Papers (TC/TP)
1	Snyder GJ	Northwestern University	USA	342	0.906	26,115	76.36
2	Wang J	Yangzhou University	China	301	0.798	5822	19.34
3	Liu Y	Hefei University	China	291	0.771	6228	21.40
4	Zhang Q	Chinese Academy of Sciences	China	283	0.75	8189	28.94
5	Chen LD	Shanghai Institute of Ceramics	China	272	0.721	15,704	57.74
6	Wang Y	University of Queensland	Australia	252	0.668	7250	28.77
7	Li J	Tsinghua University	China	245	0.649	6475	26.43
8	Kim J	Chung-Ang University	South Korea	240	0.636	5954	24.81
9	Li Y	Shenzhen University	China	240	0.636	3446	14.36
10	Zhang J	Chinese Academy of Sciences	China	232	0.615	6158	26.54
11	Zhang Y	National University of Singapore	Singapore	230	0.609	5960	25.91
12	Zhao LD	Beihang University	China	224	0.594	21,749	97.09
13	Li X	Shanghai Jiao Tong University	China	219	0.58	4836	22.08
14	Mori T	National Institute for Materials Science	Japan	219	0.58	5289	24.15
15	Tang XF	Wuhan University of Technology	China	218	0.578	6963	31.94
16	Wang L	Shenzhen University	China	217	0.575	3831	17.65
17	Zhang H	Tianjin University	China	203	0.538	4908	24.18
18	Shi X	Shanghai Institute of Ceramics,	China	197	0.522	10,482	53.21
19	Liu J	University of Groningen	Netherlands	196	0.519	4611	23.53
20	Yang J	Shanghai University	China	192	0.509	6001	31.26

on thermoelectric materials research highlights the top 20 prolific authors, led by Snyder GJ from the USA, with significant contributions from Chinese researchers like Wang J and Liu Y. The table reflects a global spread, with authors from China, the USA, Australia, South Korea, Singapore, Japan, and the Netherlands, showcasing the worldwide interest in this field. Authors like Zhao LD from China exhibit a high impact with exceptional total citations per paper ratio. The affiliations range from diverse universities to specialized institutes, indicating broad academic involvement in thermoelectric materials research. This table underscores these leading researchers’ significant contributions and influence in a globally collaborative and interdisciplinary field.

4.5. Top Leading Organizations

Figure 5 comprehensively analyzes the top 20 high-yield organizations in thermoelectric materials research, revealing a landscape marked by diverse contributions and significant impacts. The Chinese Academy of Sciences stands at the forefront, accounting for 6.28% of the total 37,739 publications in this field, alongside a notable impact of 32.89 citations per paper. These data highlight the dominant role of Chinese institutions in thermoelectric research, as further evidenced by the presence of the University of Chinese Academy of Sciences and Tsinghua University among the top ranks, signaling China’s robust engagement in this scientific area. However, the influence of thermoelectric materials research extends internationally with organizations such as the French CNRS and the United States Department of Energy reflecting the field’s global reach through their respective publication shares and citation rates. A notable aspect of these data is the variation in average citations per publication, which points to differing research strategies and impacts across these institutions. For instance, despite having fewer publications, the University of California System and Shanghai Institute of Ceramics CAS demonstrate exceptionally high citation rates per paper, indicative of pioneering or highly influential research contributions. In contrast, though ranking in the top 20, institutions like Northwestern University exhibit relatively lower citation rates, potentially indicating a focus on emerging research areas within thermoelectric materials or studies that are yet to establish a firm foothold. Overall, Figure 5 quantifies these leading organizations’ contributions and qualitatively assesses their influence, offering critical insights into academic, research, and policy-making communities in the field.

4.6. Top Leading Countries

Figure 6 shows three distinct bar charts that provide a nuanced understanding of the global contributions to thermoelectric materials research. The first chart, illustrating the ‘Record Count by Country’, establishes the People’s Republic of China as the pre-eminent leader in research output, significantly outpacing the USA and India. This high record count from China demonstrates the country’s extensive focus and robust output in this specialized field. The second chart, depicting ‘Total Citations by Country’, mirrors this trend, with China and the USA leading, signifying their prolific research activities and the substantial influence and recognition their research has garnered in the scientific community. However, the third chart, ‘Citations per Paper by Country’, reveals an intriguing aspect of the impact of research. Here, countries like Singapore, Australia, and the USA are highlighted for their high average citations per paper. Despite a lower volume of publications compared to China, the research outputs from these countries are highly cited, indicating a strong focus on quality and significant contributions to advancing the field of thermoelectric materials. Collectively, these charts paint a comprehensive picture of the global landscape in thermoelectric materials research, showcasing the intricate balance between the quantity, quality, and impact of contributions from different countries.

4.7. Country Collaboration Map

Table 3. Top 20 country collaborations in producing thermoelectric materials. Data from Web of Science (https://www.webofscience.com/wos/woscc/summary/8dc0bf2b-8a02-492e-9254-e6aac492a1ba-010e6befe7/relevance/1) (accessed on 23 November 2023) based on 37,739 publications.

From	To	Frequency
China	USA	1491
Saudi Arabia	Pakistan	468
China	Australia	449
USA	Germany	368
China	Japan	359
China	Singapore	350
China	Germany	345
China	United Kingdom	320
USA	Korea	266
Saudi Arabia	Egypt	240
China	India	190
USA	United Kingdom	186
India	Saudi Arabia	178
China	Korea	177
USA	France	172
China	Saudi Arabia	170
China	France	169
USA	India	155
China	Pakistan	154
USA	Japan	151
Germany	France	144
India	Japan	129
France	Spain	121
Korea	Saudi Arabia	111
Japan	France	99

highlights the global collaboration landscape in thermoelectric materials research, showcasing how nations partner to advance this field. The visualization of the collaboration can be seen in Figure 7. The most significant collaboration is between China and the USA, with 1491 papers underlining a robust research link. Other notable collaborations include Saudi Arabia with Pakistan and Egypt, China with Australia, Japan, Singapore, Germany, the United Kingdom, India, Korea, and France, and the USA with Germany, Korea, the United Kingdom, France, India, and Japan. These data point to the importance of international partnerships in scientific progress, clearly focusing on leading technologically countries and emerging research hubs like Saudi Arabia and India. It is a testament to how global cooperation is pivotal in scientific advancement, especially in sophisticated fields like thermoelectric materials [58,63].

4.8. Top Leading Research Area

Figure 8 shows the distribution of research outputs across various research areas in thermoelectric materials. The chart clearly shows that ‘Materials Science’ is the predominant area of research, with the highest record count, followed by ‘Physics’ and ‘Chemistry’. This distribution underscores the interdisciplinary nature of thermoelectric materials research, integrating principles from these core scientific disciplines. The prominence of ‘Materials Science’ reflects the field’s focus on developing new materials and understanding their properties, which is fundamental to advancements in thermoelectric technology.

4.9. Top Leading Research Area and Funding Agencies

Figure 9 displays the involvement of different funding agencies in supporting thermoelectric materials research. The ‘National Natural Science Foundation of China (NSFC)’ is the leading funder, indicating substantial investment in this area, particularly within China. Other significant contributors include the ‘National Science Foundation (NSF)’ and the ‘United States Department of Energy (Doe)’. This chart highlights the pivotal role of these agencies in driving research and innovation in thermoelectric materials, reflecting the strategic priorities and research funding landscapes in different regions.

4.10. Most Cited Publications

Table 4. Top 20 most cited publications on thermoelectric materials. Data from Web of Science (https://www.webofscience.com/wos/woscc/summary/8dc0bf2b-8a02-492e-9254-e6aac492a1ba-010e6befe7/relevance/1) (accessed on 23 November 2023) based on 37,739 publications.

Rank	Authors	Article Title	Source Title	Total Citation (TC)
1	Anasori, B et al.	2D metal carbides and nitrides (MXenes) for energy storage	Nature Reviews Materials	4649
2	Zhao, LD et al.	Ultralow thermal conductivity and high thermoelectric figure of merit in SnSe crystals	Nature	3668
3	He, J and Tritt, TM	Advances in thermoelectric materials research: Looking back and moving forward	Science	1577
4	Zhao, LD et al.	Ultrahigh power factor and thermoelectric performance in hole-doped single-crystal SnSe	Science	1509
5	Tan, GJ et al.	Rationally Designing High-Performance Bulk Thermoelectric Materials	Chemical Reviews	1451
6	Kim, SI et al.	Dense dislocation arrays embedded in grain boundaries for high-performance bulk thermoelectrics	Science	1400
7	Zhu, FF et al.	Epitaxial growth of two-dimensional stanene	Nature Materials	1362
8	Cahill, DG et al.	Nanoscale thermal transport. II. 2003–2012	Applied Physics Reviews	1241
9	Kim, HS et al.	Characterization of Lorenz number with Seebeck coefficient measurement	APL Materials	1167
10	Zeier, WG et al.	Engineering half-Heusler thermoelectric materials using Zintl chemistry	Nature Reviews Materials	983
11	Shi, XL; Zou, J and Chen, ZG	Advanced Thermoelectric Design: From Materials and Structures to Devices	Chemical Reviews	961
12	Kovalenko, MV et al.	Prospects of Nanoscience with Nanocrystals	ACS Nano	928
13	Khan, Y et al.	Monitoring of Vital Signs with Flexible and Wearable Medical Devices	Advanced Materials	899
14	Zhu, TJ et al.	Compromise and Synergy in High-Efficiency Thermoelectric Materials	Advanced Materials	892
15	Fu, CG et al.	Realizing high figure of merit in heavy-band p-type half-Heusler thermoelectric materials	Nature Communications	873
16	Russ, B et al.	Organic thermoelectric materials for energy harvesting and temperature control	Nature Reviews Materials	847
17	Guillon, O et al.	Field-Assisted Sintering Technology/Spark Plasma Sintering: Mechanisms, Materials, and Technology Developments	Advanced Engineering Materials	834
18	Zhao, LD; Dravid, VP and Kanatzidis, MG	The panoscopic approach to high performance thermoelectrics	Energy & Environmental Science	797
19	Vasala, S and Karppinen, M	A2B′BO6 perovskites: A review	Progress in Solid State Chemistry	792
20	Shi, H et al.	Effective Approaches to Improve the Electrical Conductivity of PEDOT:PSS: A Review	Advanced Electronic Materials	791

shows the top 20 most cited publications on thermoelectric materials, revealing significant insights into the field. High-impact journals like “Nature” and “Science” highlight the broad scientific interest in thermoelectric materials research—notably, the work by Anasori et al. [64] on 2D metal carbides and nitrides (MXenes) for energy storage leads the citations, underscoring the community’s focus on 2D materials and energy storage. Repeated appearances of authors such as Zhao LD indicate the key contributors and suggest a concentration of expertise. The variety in topics, from ultralow thermal conductivity and high thermoelectric figure of merit in materials like SnSe to broader reviews on advances in thermoelectric materials, reflects a diverse and interdisciplinary research landscape. This diversity points towards a field exploring multiple pathways, including manipulating materials at the atomic or nanoscale, to optimize thermoelectric efficiency. Additionally, including articles on emerging technologies and interdisciplinary applications, like medical devices, shows the field’s expansion beyond traditional inorganic materials [65]. Overall, this list highlights the most impactful research and sheds light on evolving trends, key focus areas, and influential contributors in thermoelectric materials research.

4.11. Analysis of All Keywords

In this section, keyword analysis was conducted, selecting 155 relevant keywords from a dataset of 54,851. This approach includes keywords from titles, abstracts, and database terms, providing a broad view of the field’s trends and themes. Although it may capture some general terms, the analysis ensures no significant research areas are overlooked. These keywords, each occurring at least 250 times, were analyzed using fractional counting to evaluate their co-occurrence links [66] resulting in 10,795 links and a total link strength of 243,149, highlighting the strong interconnectivity in the dataset. Figure 10 shows the network map of thermoelectric material research keywords. The data are grouped into four distinct clusters, each representing a concentrated area of research focus and thematic relevance. These clusters, interconnected through a complex web of relationships, provide insights into current trends and focal points in the field:

Cluster 1: Material Properties and Computational Modeling

Cluster 2: Material Synthesis and Thermoelectric Applications

Cluster 3: Thermoelectric Efficiency and Material Enhancement

Cluster 4: Thermoelectric Systems and Energy Applications

Each cluster reflects a unique aspect of the research landscape, from theoretical modeling and material properties to applied thermoelectric systems and energy efficiency. This cluster analysis serves as an insight into the multifaceted nature of this research domain, highlighting the diversity and interconnectedness of the topics under study.

Cluster 1: Material Properties and Computational Modeling

Key Themes: This cluster focuses on material properties (like electronic, optical, and mechanical properties), crystal structures, and computational modeling techniques (like density functional theory, DFT) [67].

Implications: The presence of keywords such as ‘ab initio’, ‘band-structure’, and ‘electronic-structure’ indicates a strong emphasis on fundamental research and theoretical modeling in materials science. The focus on ‘crystal-structure’, ‘microstructure’, and various properties (electronic, optical and mechanical) implies an interest in understanding and designing materials at a microscopic level for specific functionalities [68,69].

Research Trend: Integrating computational methods like DFT in exploring material properties suggests a trend toward simulation-driven material discovery and optimization [70,71].

Cluster 2: Material Synthesis and Thermoelectric Applications

Key Themes: This cluster appears to focus on material synthesis (e.g., ‘fabrication’, ‘deposition’), properties relevant to thermoelectrics (e.g., ‘Seebeck coefficient’, ‘thermal conductivity’), and specific materials like ‘bismuth telluride’ and ‘graphene’ [72].

Implications: The emphasis on ‘thermoelectric performance’ and specific materials indicates active research in improving thermoelectric materials for energy conversion applications. The presence of ‘nanostructures’ and ‘thin films’ points to exploring material structures at the nanoscale for enhancing thermoelectric properties [73].

Research Trend: There appears to be a significant interest in nanoengineering and thin film technologies, aiming to enhance the efficiency of thermoelectric materials [74].

Cluster 3: Thermoelectric Efficiency and Material Enhancement

Key Themes: Keywords like ‘lattice thermal conductivity’, ‘enhancement’, and ‘thermoelectric material’ suggest a focus on improving the efficiency of thermoelectric materials [75].

Implications: The presence of ‘phonon-scattering’, ‘thermal-conductivity’, and various material names (e.g., ‘pbte’, ‘skutterudites’) indicates research aimed at understanding and reducing lattice thermal conductivity for better thermoelectric performance [76].

Research Trend: There seems to be an emphasis on material modification and understanding heat transport mechanisms, crucial for advancing the efficiency of thermoelectric materials [13].

Cluster 4: Thermoelectric Systems and Energy Applications

Key Themes: This cluster revolves around the application of thermoelectric materials in systems and devices (e.g., ‘thermoelectric generator’, ‘energy harvesting’) and performance aspects (‘efficiency’, ‘power’) [77].

Implications: Keywords such as ‘waste heat recovery’, ‘power generation’, and ‘energy efficiency’ highlight the application of thermoelectrics in energy conversion and sustainability. This indicates a practical, application-oriented approach to utilizing thermoelectric materials [78].

Research Trend: The focus is evidently on integrating thermoelectric materials into systems for real-world applications, like waste heat recovery, indicating a move from material research to applied engineering [79].

Overall Implications and Trends

The analysis reflects a multidisciplinary approach, integrating material science, physics, engineering, and computational modeling. There is a clear progression from fundamental research in Cluster 1 to application-driven research in Cluster 4. A recurring theme across the clusters is enhancing the efficiency of materials and systems for sustainable energy applications. This analysis provides a snapshot of the current research landscape and trends in the field, potentially informing researchers, policymakers, and industry stakeholders about key focus areas and future directions.

Figure 10. Network map of thermoelectric material research keywords. Data from Web of Science (https://www.webofscience.com/wos/woscc/summary/8dc0bf2b-8a02-492e-9254-e6aac492a1ba-010e6befe7/relevance/1) (accessed on 23 November 2023) using Biblioshiny-SSSM 2023 software based on 37,739 publications.

Figure 10. Network map of thermoelectric material research keywords. Data from Web of Science (https://www.webofscience.com/wos/woscc/summary/8dc0bf2b-8a02-492e-9254-e6aac492a1ba-010e6befe7/relevance/1) (accessed on 23 November 2023) using Biblioshiny-SSSM 2023 software based on 37,739 publications.

4.12. Analysis of Author Keywords

A co-occurrence analysis of author keywords was conducted, focusing on 40,674 keywords related to “types of analysis” and “units of analysis”, with 108 meeting the minimum occurrence threshold of 100. Unlike all keywords analysis, author keywords offer a more focused view of the specific terms and themes that researchers prioritize in their work. These keywords, analyzed through both full and fractional counting methods, provide deeper insights into the core areas of interest, reflecting current advancements and emerging trends in the field [66]. This approach helps identify the most relevant research directions as defined by the experts themselves, ensuring that the analysis is closely aligned with the actual focus of studies within thermoelectric materials.

The keywords were grouped into 6 distinct clusters, with a total of 2943 links connecting them and a combined link strength of 21,340.

Figure 11 illustrates the thematic landscape of thermoelectric research by mapping author keywords using Vos viewer Software-version 1.6.19. The subsequent sections detail each cluster’s focal points, representative keywords within each cluster, and the implications of these thematic groupings.

Cluster 1: Energy Conversion and Thermoelectric Applications

Keywords: ‘thermoelectric generator’; ‘energy harvesting’; ‘solar energy’; ‘renewable energy’.

Focus: This cluster emphasizes energy conversion, thermoelectric devices, and efficiency improvements.

Implications: This suggests active research in converting various forms of energy, particularly waste heat and solar energy, into electricity using thermoelectric means. The focus on ‘optimization’ and ‘efficiency’ indicates efforts to enhance the performance of these systems [1,80].

Cluster 2: Material Synthesis and Nanostructures

Keywords: ‘bismuth telluride’; ‘carbon nanotubes’; ‘nanocomposites’; ‘thermoelectric’.

Focus: The second cluster centers on the synthesis of thermoelectric materials and the exploration of nanostructures.

Implications: This cluster indicates significant research in developing new materials and incorporating nanostructures to improve thermoelectric properties [81,82].

Cluster 3: Computational Modeling and Material Properties

Keywords: ‘density functional theory’; ‘electronic structure’; ‘semiconductors’; ‘thermoelectric properties’.

Focus: This cluster deals with computational methods and analyzing various material properties.

Implications: The presence of computational and theoretical analysis keywords indicates a strong emphasis on understanding and predicting material behavior at a fundamental level [70].

Cluster 4: Measurement and Characterization

Keywords: ‘thermal conductivity’; ‘seebeck coefficient’; ‘electrical conductivity’.

Focus: Cluster four is oriented towards the measurement and characterization of material properties.

Implications: This cluster highlights the importance of measuring key thermoelectric properties, crucial for assessing and enhancing material performance [80,83].

Cluster 5: Material Performance and Enhancement

Keywords: ‘lattice thermal conductivity’; ‘phonon scattering’; ‘zt’ (figure of merit).

Focus: The fifth cluster revolves around enhancing material performance for thermoelectric applications.

Implications: Keywords like ‘lattice thermal conductivity’ and ‘phonon scattering’ suggest a focus on understanding and reducing heat conduction in materials to improve their thermoelectric efficiency [37,83,84].

Cluster 6: Material Processing and Microstructure

Keywords: ‘spark plasma sintering’; ‘microstructure’; ‘thermoelectric materials’.

Focus: The final cluster focuses on thermoelectric materials’ processing techniques and microstructure analysis.

Implications: This indicates research into how processing methods affect the microstructure and, consequently, the properties of thermoelectric materials [37,85,86,87].

In conclusion, this cluster analysis provides a comprehensive overview of the research trends and focal areas in thermoelectric and energy conversion. From material synthesis and computational modeling to performance optimization and application in energy systems, these clusters encompass a wide range of research activities, reflecting the multifaceted nature of these thermoelectric materials.

Figure 11. Keyword interconnectivity map in thermoelectric research. Data from Web of Science (https://www.webofscience.com/wos/woscc/summary/8dc0bf2b-8a02-492e-9254-e6aac492a1ba-010e6befe7/relevance/1) (accessed on 23 November 2023) using Biblioshiny—SSSM 2023 software based on 37,739 publications.

Figure 11. Keyword interconnectivity map in thermoelectric research. Data from Web of Science (https://www.webofscience.com/wos/woscc/summary/8dc0bf2b-8a02-492e-9254-e6aac492a1ba-010e6befe7/relevance/1) (accessed on 23 November 2023) using Biblioshiny—SSSM 2023 software based on 37,739 publications.

Figure 12 shows the distribution of total keyword occurrences within the six research clusters identified in the co-occurrence analysis. Each bar represents the total number of keywords mentioned within its respective cluster, highlighting the focus of research efforts across different thematic areas. The varying heights of the bars indicate the relative concentration of research activities, with Cluster 2, “Material Synthesis and Nanostructures” having the highest keyword occurrences, followed closely by Cluster 1, “Energy Conversion and Thermoelectric Applications”. This distribution suggests that a significant portion of the research is dedicated to developing new materials and exploring nanoscale properties for improving thermoelectric performance. Meanwhile, clusters such as “Material Performance and Enhancement” and “Material Processing and Microstructure” have fewer keyword occurrences, reflecting a more specialized or niche focus within the overall field.

5. Conclusions

This study provides a comprehensive scientometric analysis of thermoelectric materials research over the past decade, providing insights into both the quantitative growth and the evolving thematic focus within the field. By examining over 37,739 publications, I identified 6 key research clusters—energy conversion, material synthesis and nanostructures, computational modeling, material properties, performance enhancement, and processing and microstructure—that encapsulate the diversity of the field. These clusters reveal a dynamic research landscape where the convergence of material science, nanotechnology, and computational methods drives innovation in energy efficiency and sustainable technologies.

The global thermoelectric materials research community has grown significantly, with China and the USA emerging as dominant contributors. However, the collaborative networks that extend across countries such as Japan, Germany, and Saudi Arabia point out the increasingly international nature of this research. The breadth of geographical contributions underscores the critical role of thermoelectric materials in addressing global energy challenges, with applications ranging from waste heat recovery to advanced cooling systems. As the demand for renewable energy sources continues to rise, these materials offer promising solutions to energy conversion and management issues, positioning them at the forefront of sustainable technological development.

These findings emphasize that thermoelectric materials research is not merely expanding in volume but evolving in focus. While early research concentrated heavily on basic material properties and energy conversion, recent studies have pivoted toward optimizing performance through nanostructuring, improving computational modeling techniques, and refining fabrication processes. The growing interest in environmentally friendly, abundant, and cost-effective materials—such as magnesium-based thermoelectric materials—indicates a shift toward sustainability. This trend aligns with the global push for cleaner technologies and reflects the field’s responsiveness to ecological imperatives.

The bibliometric trends identified in this analysis further highlight the increasing impact of thermoelectric research. Significant growth in both publication and citation numbers—peaking in 2021—points to the field’s continued relevance and the recognition of its contributions to solving critical energy issues. Despite a slight decline in publication numbers post-2021, likely due to external economic or global disruptions, the robust foundation of research laid over the past decade ensures that thermoelectric materials remain a vital area of investigation with the potential for technological advancements.

Looking ahead, the integration of artificial intelligence and machine learning techniques with experimental research presents an exciting frontier. These approaches could accelerate the discovery of new thermoelectric materials and optimize existing ones, enabling even greater energy efficiency. Additionally, applying thermoelectric materials in novel domains, such as flexible electronics and medical devices, expands their potential impact beyond traditional energy systems. This evolution will require continued interdisciplinary collaboration and targeted investments in research infrastructure.

In conclusion, thermoelectric materials research, driven by global collaborations and advanced scientific methodologies, is poised to play a pivotal role in the future of sustainable energy technologies. The thematic shifts identified in this study underscore the field’s potential to contribute meaningfully to fundamental scientific understanding and practical energy solutions. As this research area continues to advance, it will likely offer innovative pathways to address the pressing global challenges of energy efficiency and sustainability.