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Review

Low-Cost Room-Temperature Perovskite Solar Cells Suitable for Continuous Production

by
Gang Wang
1,*,
Weikui Li
1,
Hang Xu
1 and
Qunliang Song
2,*
1
School of Science, Chongqing University of Technology, Chongqing 400054, China
2
School of Materials and Energy, Institute for Clean Energy and Advanced Materials, Southwest University, Chongqing 400715, China
*
Authors to whom correspondence should be addressed.
Electronics 2023, 12(21), 4498; https://doi.org/10.3390/electronics12214498
Submission received: 18 September 2023 / Revised: 25 October 2023 / Accepted: 31 October 2023 / Published: 1 November 2023
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Abstract

:
Perovskite solar cells have garnered significant attention as the next-generation photovoltaic devices. After more than a decade of dedicated research, commercializing these cells is now on the horizon. One of the primary focuses for developers aiming at large-scale industrial production is cost reduction. To achieve cost savings in perovskite solar cell manufacturing, researchers have successfully devised cost-effective room-temperature perovskite solar cells for fabricating perovskite films at room-temperature. Additionally, they have developed full room-temperature perovskite solar cells, where the entire solar cell is fabricated at room temperature. These cells excel in terms of their straightforward processing, low energy consumption, and continuous production capability, rendering them highly suitable for industrial applications. This article is intended to provide an overview of the latest advancements in room-temperature perovskite solar cell research. It will summarize commonly utilized methods for their fabrication, delve into the significant implications of full room-temperature perovskite solar cells for the commercialization of perovskite solar technology, and conclude by outlining various production techniques for room-temperature perovskite films. Furthermore, this article will offer insights into the future development directions of room-temperature perovskite solar cells and full room-temperature perovskite solar cells.

1. Introduction

In recent years, perovskite solar cells (PSCs) have captured extensive attention from both the academic and industrial sectors. Thanks to the advantages of high light absorption coefficients [1,2], long carrier transport distances [3,4] and low exciton binding energies [5,6] exhibited by perovskite materials, the conversion efficiency of PSCs has steadily improved over the past decade [7,8,9,10], with laboratory-certified efficiencies reaching as high as 26.1% for small-scale devices [11]. The rapid development of high-efficiency perovskite solar cells positions them as the most promising next-generation photovoltaic devices. However, the commercialization of PSCs continues to encounter various challenges, encompassing low efficiency in large-area cells, long-term stability concerns, the toxicity of heavy metal lead, and production cost considerations [12,13,14,15]. These factors collectively underscore critical research areas in the field of PSCs.
The production cost is a crucial factor to consider in the commercialization of perovskite solar cells, making the effective reduction in production costs a significant focus of research in the field. The production cost of PSCs is closely tied to the PSCs fabrication process. Currently, there are several production methods for PSCs, including solution process, thermal evaporation, and vapor-assisted process [16,17,18,19,20]. Among these, thermal evaporation requires a high-vacuum environment, imposing stringent equipment requirements. The vapor-assisted process typically demands extended reaction times to obtain perovskite films. In comparison to the aforementioned production processes, the solution process exhibits lower equipment requirements and a simpler preparation procedure, making it the most widely used method for PSCs production [14,18,20,21,22]. The solution process offers the flexibility to produce PSCs with various specifications, utilizing techniques such as spin-coating, blade-coating, spray-coating, roll-to-roll, and printing [14,23,24,25,26]. Blade-coating, spray-coating, roll-to-roll, and printing are particularly suitable for large-scale perovskite solar cell production. These methods have shown great potential for cost-effective manufacturing of large-area PSCs.
Although the current solution-based production process provides significant cost advantages, there is still room for further cost reduction. Enhancing the solution-based perovskite solar cell production process by streamlining manufacturing steps could greatly advance the production and application of low-cost perovskite solar cells. As shown in Figure 1, the conventional solution-based fabrication process can typically be broken down into three key steps: (1) preparation of precursor solutions, (2) deposition of films onto substrates, and (3) thermal annealing to facilitate crystal transformation and attain high-quality perovskite films. Within these steps, thermal annealing plays a pivotal role in achieving high-efficiency PSCs production. Nevertheless, the thermal annealing process introduces specific challenges in the development of PSCs. Depending on the specific perovskite compositions and solvent used, the annealing temperature, duration, and environmental conditions for PSCs should vary considerably. For example, the typical annealing temperature for PSCs currently falls within the range of 80–150 °C, with annealing times typically spanning from 10 to 60 min. In the case of high-efficiency two-step PSCs based on the FAI, film deposition occurs in an inert environment, followed by annealing in conditions with approximately 30% humidity, which adds complexity to the production process. These variations in annealing temperature, duration, and environmental conditions not only complicate the fabrication process but also result in increased energy consumption, extended production times, and elevated production costs.
To mitigate the adverse impacts of thermal annealing and further streamline the production of PSCs, researchers have successfully devised room-temperature PSCs (RT-PSCs, fabricating perovskite films at room temperature) production techniques [27,28,29,30,31,32,33]. These methods aim to simplify the manufacture of solution-based PSCs, resulting in reduced energy consumption, shorter production times, and decreased production costs. RT-PSCs offer the dual advantage of simplifying the manufacturing process and mitigating the detrimental effects of thermal annealing on perovskite film quality. Extending from this groundwork, researchers have achieved the fabrication of all functional layers in PSCs at room temperature, encompassing the electron transport layer, perovskite layer, and hole transport layer, resulting in the creation of full RT-PSCs (FRT-PSCs). This holistic methodology optimizes the seamless production of PSCs by enabling the uninterrupted deposition of thin films for all functional layers, offering substantial potential for the industrial-scale advancement of large-area PSCs. Considering the advantages and future prospects of RT-PSCs and FRT-PSCs, understanding the latest research advancements in this field is of significant importance for promoting the commercialization of cost-effective PSCs. Therefore, in this article, we provide an overview of the latest research progress in solution-based RT-PSCs to further bolster their commercialization. We summarize the methods employed in RT-PSC fabrication, discuss the developmental trajectories of FRT-PSCs, emphasizing their pivotal role in PSC commercialization, evaluate various room-temperature perovskite film production techniques, and offer insights into the future directions of RT-PSCs and FRT-PSCs.

2. Room-Temperature PSCs

The quality of perovskite films plays a crucial role in determining the efficiency of solar cells. Achieving high-quality perovskite films without thermal annealing is a crucial factor in the development of RT-PSCs. Currently, researchers primarily employ techniques such as vacuum deposition, ultrasonic vibration, vacuum assistance, and solvent engineering to fabricate high-quality room-temperature perovskite films [27,30,31,34,35]. While methods such as vacuum deposition, ultrasonic vibration, and vacuum assistance eliminate the requirement for thermal annealing, they often rely on additional auxiliary equipment or processes to promote the crystallization of perovskite films. In contrast, solvent engineering-based RT-PSCs typically do not necessitate supplementary equipment during the fabrication process, making them more cost-effective and technologically straightforward. Consequently, they are better suited for the development of low-cost PSCs. Table 1 presents the most recent research findings related to RT-PSCs using the partial solution method. In this section, we present a comprehensive review and discussion of the production methods and research advancements in RT-PSCs based on solvent engineering.

2.1. Antisolvent Engineering for RT-PSCs

The typical polar aprotic solvents used for processing perovskites, such as N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and N-methylpyrrolidone (NMP), can establish strong coordination bonds with Pb atoms. This results in the formation of a stable intermediate phase structure within the perovskite solution [25,45]. Typically, the removal of residual solvents from the film through thermal annealing is required to facilitate the transformation of the crystal structure. However, room-temperature perovskite films often utilize non-thermal processing techniques to facilitate the transition of the intermediate phase and achieve high-quality perovskite films. Antisolvent engineering is a widely employed approach for enhancing the efficiency of PSCs [46]. Moreover, it proves to be an effective technique for the fabrication of RT-PSCs. During the thin film preparation process, the attainment of high-quality room-temperature perovskite films is facilitated by the rinsing or immersion in an antisolvent, as illustrated in Figure 2. The volatile nature of the antisolvent aids in eliminating residual solvents like DMF, DMSO, and NMP from the film, thereby promoting the transformation of the intermediate phase into a perovskite crystal [47,48]. Since different solvents and antisolvents have distinct properties, the quality of antisolvent room-temperature perovskite films is closely associated with the selection of the perovskite solution and antisolvent [48].
Yin et al. [49] conducted research in the GBL and DMSO mixed solvent and discovered that ethyl acetate is more suitable for RT-PSCs compared to toluene. During the high-speed spin-coating process, DMSO will be efficiently eliminated from the film by rinsing with ethyl acetate, thereby preventing the formation of the PbI2-MAI-DMSO intermediate phase (as depicted in Figure 3a) and enabling the production of high-quality room-temperature perovskite films comparable to those obtained through thermal annealing (as shown in Figure 3b–d). Their study has unveiled a significant relationship between the quality of room-temperature perovskite films and the choice of antisolvent. They discovered that using ether acetate as an antisolvent enables the production of high-quality room-temperature perovskite films. Conversely, when toluene serves as the antisolvent, the film’s crystal structure remains unaltered at room temperature (Figure 3e). Consequently, RT-PSCs utilizing ether acetate achieve an efficiency comparable to thermally annealed cells, reaching 15.58%. In contrast, the efficiency of RT-PSCs employing toluene as the antisolvent is a mere 7.55% (Figure 3f). This underscores the critical importance of selecting the appropriate antisolvent for RT-PSCs.
Fang et al. [39] conducted a comprehensive investigation into the influence of DMAc/DMSO and DMAc/NMP cosolvents on the crystallization of room-temperature MAPbI3 perovskite films. They observed that toluene effectively removed NMP from the PbI2-MAI-NMP intermediate phase in the film. This led to an immediate crystallization process and complete transformation of the crystal structure. However, toluene demonstrated limited capacity to extract DMSO, preventing the full conversion of the PbI2-MAI-DMSO intermediate phase into a perovskite crystal, as shown in Figure 4a,b. Consequently, DMAc/NMP solvent yielded highly efficient RT-PSCs, with an efficiency of 17.09%, significantly outperforming devices based on DMAc/DMSO (3.81% efficiency), as shown in Figure 4c. Simultaneously, RT-PSCs demonstrate comparable long-term stability to thermally annealed PSCs (Figure 4d). Zhou et al. [37] discovered that ethyl acetate is highly miscible with NMP and does not dissolve perovskite. Therefore, ethyl acetate can effectively extract NMP from the film, inducing a transformation of the film crystallization. They successfully fabricated RT-PSCs with a 15.2% efficiency by immersing the NMP solution-coated film in ethyl acetate in an environment with approximately 30% humidity.
Zhu et al. [50] proposed an intermediate phase molecular exchange strategy to prepare RT-PSCs. The intermediate phase film obtained by the antisolvent method was rinsed again with isopropanol (IPA) solution containing MACl/MAI. Due to the stronger affinity of MACl/MAI for DMSO and PbI2, MACl/MAI can replace DMSO in the intermediate phase film during the rinsing process. The replaced DMSO was extracted from the film with IPA, resulting in a complete transformation of the perovskite film at room temperature. At the same time, MACl/MAI was able to further repair defects in the film to obtain high-quality room-temperature perovskite films. Ultimately, this approach yielded RT-PSCs with an efficiency of 19.45%, surpassing the efficiency achieved through thermal annealing (17.03%).
Similar to the impact of solvent components, the composition of perovskite also plays a crucial role in the crystalline transformation of room-temperature films. By regulating the presence of dopant elements, it is possible to modify the binding energy between solutes and solvents or induce crystal structure transformation at room temperature. Matsui et al. [40] reported that Cs+ ions can substitute for solvents like DMSO and form strong coordination bonds with [PbI6]4−. This phenomenon enhances the evaporation of residual solvents within the film and facilitates the crystalline transformation of the perovskite film at room temperature, as illustrated in Figure 5a. Their research indicates that the inclusion of MA and Cs effectively augments the grain size and surface smoothness of room-temperature perovskite films (Figure 5b). Simultaneously, when the Cs content is below 10%, the perovskite film’s crystal structure does not undergo complete transformation (Figure 5c). By adjusting the Cs content in the composition, they successfully produced high-quality FA perovskite films at room temperature, achieving solar cell efficiencies of 18.1% (mesoporous TiO2, Figure 5d) and 17.3% (planar SnO2, Figure 5e) at room temperature. Lv et al. [35,51] effectively controlled the crystallization process of room-temperature perovskite films by varying the Br content in the perovskite. This approach enabled them to attain an efficiency of 19.59% for FA PSCs at room temperature (35–40 °C).

2.2. Vapor-Assisted for RT-PSCs

Researchers have found that exposing unannealed films to a specific humidity level can result in the formation of a more active metastable phase, MAPbI3·H2O. This transitional intermediate phase readily transforms into high-quality perovskite crystals as moisture evaporates [36]. Therefore, subjecting the film to an appropriate humidity environment can leverage water vapor to aid in film crystallization and facilitate crystal structure transformation, ultimately leading to high-quality room-temperature perovskite films. Dubey et al. [52] observed that when films are exposed to the atmosphere, DMSO from MAI-PbI2-DMSO dissolves into the ambient moisture and escapes with water evaporation, prompting the conversion of the intermediate phase into perovskite crystals. After 5 h of exposure to air, they obtained nanorod-shaped perovskite films, achieving a room-temperature cell efficiency of 16.83%. Wang et al. [38] report a water-vapor annealing (WVA) method at room temperature for the formation of high-crystallinity and void-free MAPbI3 perovskite films (as illustrated in Figure 6a). Figure 6b illustrates the mechanisms of crystal growth processes in a perovskite film: (1) Water molecules are absorbed on the perovskite surface, mediating strong hydrogen bonding between methylammonium cations and the Pb-I cage. (2) Hydrolysis of perovskite into PbI2 and MAI by water. (3) Restraining MAI from reacting with nearby PbI2 to reform perovskite after water evaporates. They conducted a comprehensive study on the influence of environmental humidity and exposure duration on the quality of room-temperature perovskite films and determined that exposing the film for 60 min under relative humidity conditions ranging from 36% to 43% resulted in the highest crystalline quality, as depicted in Figure 6c–h. Ultimately, they achieved room-temperature perovskite solar cells with a higher conversion efficiency (16.39%) compared to thermally annealed ones (12.88%), as shown in Figure 6i.
Compared to using moisture-assisted crystallization with exposure to air, a mixed solvent atmosphere can induce the transformation of the crystal structure of thin films more rapidly. Yu et al. [53] discovered that employing a 1:20 volume ratio of DMF/CB mixed solvents for vapor-assisted crystallization can completely transform the film’s crystal structure at room temperature within 6 min, resulting in a 16.4% efficiency for RT-PSCs. Although mixed solvents can accelerate the formation of perovskite films, it remains necessary to let the film thoroughly dry at room temperature for 12 h, which is not conducive to the efficient production of perovskite solar cells.
The coordination relationship between solvents and solutes or the activation energy for film structure transformation is a crucial factor influencing the crystallization process of room-temperature perovskite films. Altering the coordination binding energy of solutes in the film or reducing the activation energy for crystal structure transformation is another essential direction for researching RT-PSCs. By utilizing ligand exchange and lowering the activation energy, it is possible to effectively obtain room-temperature perovskite films. Zhang et al. [41] discovered that treating PbI2 with pyridine (Py) enhances the formation of high-quality room-temperature perovskite films. As depicted in Figure 7a–e, PbI2 treated with pyridine vapor exhibited a porous structure within the PbI2.(Py)2 film. This porous structure facilitates the diffusion of organic molecules like FAI into the PbI2 film, resulting in the formation of high-quality perovskite crystals [54]. Consequently, after pyridine vapor treatment, the grain size of the perovskite film is twice that of the reference sample, leading to a significant improvement in film quality. Compared to PbI2, PbI2.(Py)2 had a lower activation energy for transformation into MAPbI3, allowing MAI to replace (Py)2 and form high-quality perovskite crystals at room temperature (as shown in Figure 7f,g). Based on this, they prepared RT-PSCs with the structure ITO/NiOx/MAPbI3/C60/Bis-C60/Ag, achieving an efficiency of 17.10%. They conducted further research on the impact of ligands formed by PbI2 with Py, DMSO, DMF, TBP, and EDA on the quality of room-temperature perovskite films and their crystallization kinetics. The ideal ligands should simultaneously have the following: (1) Good reactivity (i.e., low activation energy and negative formation enthalpy) to form perovskite from PbI2(L)x intermediates. (2) High volatility (or low boiling point). (3) Low solubility of PbI2. (4) Small molecular size [55].

2.3. Novel Solvent for RT-PSCs

Because traditional solvents like DMF, DMSO, and NMP have high boiling points and form stable intermediate phase structures in the film, it is typically required to employ additional processes to evaporate the remaining solvents in the film and promote the transformation of the crystal structure. This constraint hinders the advancement of RT-PSCs utilizing traditional solvents. To tackle this challenge, researchers have developed novel solvents, such as acetonitrile (ACN), 1,2-dimethoxyethane (DME), tetrahydrofuran (THF), mixtures of methylamine in ethanol (ME) in combination with a secondary solvent (ACN, or THF), 2-methoxyethanol (2-ME), and gamma-valerolactone (GVL), which are better suited for the fabrication of RT-PSCs [28,56,57,58,59,60,61,62]. These solvents possess properties such as low boiling points, volatility, and the absence of stable intermediate phases. They can rapidly evaporate from the thin film at room temperature, facilitating the formation of perovskite thin films with complete crystal structure transformation. When working with novel solvents, it is common practice to blend multiple solvents. This enhances the processability of the perovskite solution and improves the quality of perovskite films by either increasing solubility or preventing phase separation within the solution.
As illustrated in Figure 8a–c, Liu et al. [42] introduced an innovative solvent for RT-PSCs, which is a mixture of ME and THF, abbreviated as TME. TME evaporates rapidly during the preparation process, allowing the MAPbI3 solution to promptly attain supersaturation and generate a multitude of nuclei, resulting in a dense and high-quality film. Furthermore, the TME solvent does not manifest intermediate phase structures, enabling the film to completely transition into a perovskite crystal structure at room temperature. Capitalizing on this, they achieved an impressive 20% conversion efficiency for RT-PSCs without any additional processing (Figure 8d). Additionally, they also realized a remarkable efficiency of 15.6% for large-area (10 cm2) RT-PSCs based on the TME solvent (Figure 8e). Wang et al. dissolved MAPb(I1 − xClx)3 single crystals in a solution containing ME and ACN to create perovskite ink. Utilizing this ink, they achieved isothermal crystallization at room temperature, resulting in the formation of compact and high-quality perovskite films (as depicted in Figure 9a–c). Based on this new type of perovskite ink, the efficiency of n-i-p and p-i-n RT-PSCs reached 22.3% and 23.1%, respectively (as demonstrated in Figure 9d,e), surpassing that of traditional thermal annealing PSCs [44].

3. Full Room-Temperature PSCs

Expanding on the advancements made in room-temperature perovskite thin film research, the attainment of room-temperature production techniques for all of the functional layers in PSCs holds the promise of realizing FRT-PSCs. This breakthrough will facilitate a seamless, cost-efficient production process across the various manufacturing stages of PSCs, resulting in substantial reductions in production expenses and a marked enhancement in overall production efficiency. In both n-i-p and p-i-n PSCs structures, aside from the perovskite layer, various functional layers play crucial roles, including charge transport layers (such as TiO2, ZnO, NiOx, SnO2, Spiro-OMeTAD, PEDOT:PSS, PTAA, P3HT, PCBM, C60, etc.), modification layers (mainly incorporating BCP, LiF, MnO3, etc.), and electrodes (Au, Ag, Al, Cu, and carbon electrodes, etc.). Metal electrodes (Au, Ag, Al, and Cu) and modification layers (LiF and MnO3) are conventionally prepared through physical vapor deposition techniques, while other functional layers can typically be prepared using straightforward solution-based methods. Therefore, the development of room-temperature charge transport layers represents another crucial research direction for realizing full room-temperature PSCs. Commonly used charge transport materials in high-efficiency PSCs are metal oxides (such as TiO2, ZnO, NiOx and SnO2), but these materials often require high-temperature treatments ranging from 150 to 500 °C. In an effort to reduce the production costs of PSCs, researchers have conducted in-depth investigations into low-temperature or room-temperature metal oxide charge transport layers using techniques like magnetron sputtering, thermal evaporation, organic-inorganic composites, precursor regulation, and UV-ozone treatment [63,64,65,66,67,68,69].
Despite significant progress in the development of room-temperature charge transport layers and room-temperature perovskite film research, the integration of both aspects to achieve full room-temperature PSCs is still in its early stages [70]. For instance, Jiang et al. [71] employed UV-ozone treatment instead of thermal annealing to obtain room-temperature Nb2O5-TiO2 electron transport layers. When combined with room-temperature perovskite films prepared using the antisolvent method, they achieved conversion efficiencies of 15.25% for rigid and 13.60% for flexible full room-temperature PSCs. Dong et al. [72] obtained room-temperature electron transport layers by subjecting solution-processed SnO2 films to 30 min of UV-ozone treatment. They controlled the crystallization process of room-temperature perovskite films using GAI doping and antisolvent methods, resulting in a remarkable conversion efficiency of 19.25% for full room-temperature PSCs.
In comparison to metal oxides, achieving RT-PSCs fabrication is more straightforward with organic materials serving as charge transport layers. Wang et al. [38] utilized untreated PEDOT:PSS as the charge transport layer and achieved an impressive 16.4% efficiency for FRT-PSCs. Cassella et al. [73] observed that PSCs prepared under room-temperature conditions and those prepared with thermal annealing using MeO-2PACz as the hole transport layer exhibited nearly identical conversion efficiencies. The different perovskite solar cell preparation processes are shown in Figure 10a. Based on the MeO-2PACz hole transport layer and the novel solvent system of 2-ME/TFH, they achieved thermal annealed cells, RT-PSCs, and FRT-PSCs with efficiencies of 18.4%, 18.0%, and 17.1%, respectively, all displaying the ability to maintain stable outputs (Figure 10b–d). The entire fabrication process of the FRT-PSCs mentioned above does not require additional auxiliary steps such as thermal annealing. Each functional layer of the cell can be continuously prepared in sequence. As shown in Figure 11, based on FRT-PSCs, a continuous production process for perovskite solar cells can be developed, further achieving the continuous production of perovskite solar cell components. This will significantly enhance the production efficiency of perovskite solar cells and effectively reduce the production costs.

4. Summary and Outlook

PSCs have emerged as prominent representatives of the next generation of photovoltaic devices, offering promising applications across various fields. Achieving high-efficiency PSCs production at room temperature presents numerous advantages, including streamlined processes, time and energy savings, increased production capacity, and reduced manufacturing costs. These benefits are particularly conducive to the large-scale commercialization of PSCs. This article primarily provides an overview of the research progress in room-temperature PSCs and highlights the advantages of complete room-temperature PSCs. It summarizes research methodologies for commonly used room-temperature PSCs, focusing on the following three aspects: (1) Antisolvent Engineering for RT-PSCs: This approach involves the fabrication of films through antisolvent engineering, which includes rinsing or immersion in solvents. These techniques effectively remove residual solvents and induce a transformation in the crystal structure of the film, resulting in the production of high-quality room-temperature perovskite films. The careful selection of an appropriate solvent system is pivotal for achieving success in producing high-quality RT-PSCs through this approach. Nevertheless, when applied to large-scale cell production, this technique encounters significant challenges. Therefore, further research aimed at adapting it for industrial-scale perovskite solar cell manufacturing is a noteworthy research direction. (2) Vapor-assisted for RT-PSCs: By exposing solution-processed films to controlled humidity conditions, a metastable phase known as MAPbI3·H2O can be formed. With subsequent moisture evaporation, high-quality perovskite films are obtained. However, this moisture-assisted crystallization process typically takes from minutes to hours, making it unsuitable for high-efficiency commercial applications. In contrast, utilizing pyridine to treat PbI2 films, forming low activation energy ligands like PbI2(Py)2 and subsequently conducting a swift exchange with MAI, can accelerate and enhance the production of room-temperature perovskite films. Further advancement of this approach requires the development of ligands characterized by high volatility, which facilitates the exchange of organic salts with low activation energy. (3) Novel Solvent for Room-Temperature PSCs: Researchers have innovated solvent systems such as ACN, TME, 2-ME, THF, DME, and GVL. These novel solvent systems offer advantages like low boiling points, easy volatility, and the absence of stable intermediate phases. They swiftly evaporate from the film at room temperature, facilitating a complete transformation of the film’s crystal structure into a perovskite film. The use of these novel solvent systems has led to the development of the most efficient room-temperature PSCs to date. Furthermore, this strategy aligns with large-scale production methods like blade-coating, making it the most suitable approach for preparing room-temperature PSCs for industrial applications.
In summary, substantial advancements have been made in the research of RT-PSCs, with record efficiencies of up to 23%. However, the current prevalent production techniques for these cells, such as the antisolvent and atmosphere-assisted methods, while capable of manufacturing RT-PSCs, do not present notable advantages in terms of production processes and preparation time when compared to traditional thermally annealed perovskite solar cells. Therefore, there is a pressing need for further development and refinement of these methods. Conversely, novel solvent-based approaches for preparing RT-PSCs offer a more streamlined manufacturing process and can yield efficient cells suitable for large-scale production. Consequently, future research endeavors should prioritize the development of solvent systems tailored for RT-PSCs to boost efficiency and broaden their applicability. Moreover, the field of FRT-PSCs remains in its infancy. While the process itself is relatively straightforward, the attained cell efficiencies are generally modest. One of the most significant challenges lies in the preparation of room-temperature charge transport layers, an area where only a few research groups have reported findings. Hence, the development of innovative charge transport materials and preparation techniques suited for room-temperature fabrication becomes a pivotal research direction, propelling the advancement of full room-temperature perovskite solar cells and facilitating continuous production.

Author Contributions

Conceptualization, Q.S.; writing—original draft preparation, G.W., W.L. and H.X.; writing—review and editing, Q.S., G.W., W.L. and H.X. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Scientific Research Foundation of Chongqing University of Technology (Grant No. 2020ZDZ012).

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. The schematic of the perovskite film fabrication process.
Figure 1. The schematic of the perovskite film fabrication process.
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Figure 2. Schematic of antisolvent immersion (a) and rinsing (b) for RT-PSC fabrication.
Figure 2. Schematic of antisolvent immersion (a) and rinsing (b) for RT-PSC fabrication.
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Figure 3. (a) Schematic diagram of the instant-crystallization mechanism for room-temperature films and (b) X-ray diffraction patterns of perovskite films prepared by dripping ethyl acetate (EA) with 100 °C annealing and without annealing (RT); scanning electron micrographs (SEM) of (c) thermally annealed (d) and room-temperature perovskite films preparing with EA, (e) MAPbI3 perovskite films prepared with toluene and EA at room temperature and annealing at 100 °C for 10 min, and (f) J−V curves of RT-PSCs prepared with EA and toluene, without annealing [49].
Figure 3. (a) Schematic diagram of the instant-crystallization mechanism for room-temperature films and (b) X-ray diffraction patterns of perovskite films prepared by dripping ethyl acetate (EA) with 100 °C annealing and without annealing (RT); scanning electron micrographs (SEM) of (c) thermally annealed (d) and room-temperature perovskite films preparing with EA, (e) MAPbI3 perovskite films prepared with toluene and EA at room temperature and annealing at 100 °C for 10 min, and (f) J−V curves of RT-PSCs prepared with EA and toluene, without annealing [49].
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Figure 4. (a) The schematic illustrations of perovskite formed from DMAc/DMSO and DMAc/NMP cosolvents, respectively. (b) XRD patterns of RT perovskite films made from DMAc/DMSO and DMAc/NMP, and the insets show the corresponding photographs. (c) J−V curves of RT-PSCs. (d) Long-term stability of RT-PSCs and annealing PSCs.
Figure 4. (a) The schematic illustrations of perovskite formed from DMAc/DMSO and DMAc/NMP cosolvents, respectively. (b) XRD patterns of RT perovskite films made from DMAc/DMSO and DMAc/NMP, and the insets show the corresponding photographs. (c) J−V curves of RT-PSCs. (d) Long-term stability of RT-PSCs and annealing PSCs.
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Figure 5. (a) Illustration of procedures with Cs and without Cs for crystalline perovskite film formation by antisolvent processing. (b) SEM images of FA0.8MA0.2 − xCsx films for various Cs contents and FA0.9MA0Cs0.1 at room temperature. (c) XRD analysis for FA0.8MA0.2 − xCsx films of varying Cs content x without annealing (δ represents the intermediate phase). J−V curve and maximum power point tracking of the champion FA0.8MA0.1Cs0.1 device without annealing on (d) mesoporous TiO2 and (e) planar SnO2.
Figure 5. (a) Illustration of procedures with Cs and without Cs for crystalline perovskite film formation by antisolvent processing. (b) SEM images of FA0.8MA0.2 − xCsx films for various Cs contents and FA0.9MA0Cs0.1 at room temperature. (c) XRD analysis for FA0.8MA0.2 − xCsx films of varying Cs content x without annealing (δ represents the intermediate phase). J−V curve and maximum power point tracking of the champion FA0.8MA0.1Cs0.1 device without annealing on (d) mesoporous TiO2 and (e) planar SnO2.
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Figure 6. Schematic diagram of (a) the preparation procedure of perovskite films with room-temperature water vapor annealing and (b) the crystal growth processes in a perovskite film. SEM images of the perovskite films treated by water-vapor annealing in the (c) RH% < 10%, (d) RH% = 33–36%, (e) RH% = 33–42%,(f) RH% = 36–43%, (g) RH% = 36–51%, and (h) thermal annealing in air (RH% < 10%); (i) J−V curves for thermal annealing (TA) and WVA PSCs [38].
Figure 6. Schematic diagram of (a) the preparation procedure of perovskite films with room-temperature water vapor annealing and (b) the crystal growth processes in a perovskite film. SEM images of the perovskite films treated by water-vapor annealing in the (c) RH% < 10%, (d) RH% = 33–36%, (e) RH% = 33–42%,(f) RH% = 36–43%, (g) RH% = 36–51%, and (h) thermal annealing in air (RH% < 10%); (i) J−V curves for thermal annealing (TA) and WVA PSCs [38].
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Figure 7. (a) Schematics of the pyridine-promoted formation of MAPbI3 film. Top-view SEM images of (b) pristine PbI2 and (c) PbI2.(Py)2; MAPbI3 films from (d) PbI2 and (e) PbI2.(Py)2 films. (f) XRD of PbI2 film, PbI2.(Py)2 film, and relevant perovskite films. (g) The reaction coordinate diagram of the perovskite formation via the conventional pathway and pyridine-promoted pathway [41].
Figure 7. (a) Schematics of the pyridine-promoted formation of MAPbI3 film. Top-view SEM images of (b) pristine PbI2 and (c) PbI2.(Py)2; MAPbI3 films from (d) PbI2 and (e) PbI2.(Py)2 films. (f) XRD of PbI2 film, PbI2.(Py)2 film, and relevant perovskite films. (g) The reaction coordinate diagram of the perovskite formation via the conventional pathway and pyridine-promoted pathway [41].
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Figure 8. (a) Photos of MAPbI3 crystals dissolved in THF, ME, and TME (THF:ME = 0.9:1), with the expected concentration of 2.1 M. (b) Comparison of intermediate-dominated crystallization in DMF and direct crystallization in TME. (c) Large-area MAPbI3 film (190 mm × 320 mm) on FTO prepared by blade-coating a 0.6 M solution of MAPbI3 in TME at room temperature. J−V curves of the (d) 0.1 cm2 device and (e) 10 cm2 series module [42].
Figure 8. (a) Photos of MAPbI3 crystals dissolved in THF, ME, and TME (THF:ME = 0.9:1), with the expected concentration of 2.1 M. (b) Comparison of intermediate-dominated crystallization in DMF and direct crystallization in TME. (c) Large-area MAPbI3 film (190 mm × 320 mm) on FTO prepared by blade-coating a 0.6 M solution of MAPbI3 in TME at room temperature. J−V curves of the (d) 0.1 cm2 device and (e) 10 cm2 series module [42].
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Figure 9. Snapshots showing the rapid RT isothermal crystallization (a) during handwriting on paper and (b) in a blade-coated film. (c) Microscopic features of the RT isothermally crystallized film in a top-view. (i) J−V characteristics and (ii) stabilized power output for RT perovskite- and TA perovskite-based (d) n-i-p and (e) p-i-n device. [44].
Figure 9. Snapshots showing the rapid RT isothermal crystallization (a) during handwriting on paper and (b) in a blade-coated film. (c) Microscopic features of the RT isothermally crystallized film in a top-view. (i) J−V characteristics and (ii) stabilized power output for RT perovskite- and TA perovskite-based (d) n-i-p and (e) p-i-n device. [44].
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Figure 10. (a) Schematic illustration of the fabrication process for annealed, room-temperature, and full room-temperature PSCs. J−V curve (i) and stabilized power output of the best performing (ii) for annealed (b), room-temperature (c), and full room-temperature (d) PSCs.
Figure 10. (a) Schematic illustration of the fabrication process for annealed, room-temperature, and full room-temperature PSCs. J−V curve (i) and stabilized power output of the best performing (ii) for annealed (b), room-temperature (c), and full room-temperature (d) PSCs.
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Figure 11. Schematic of continuous production of FRT-PSCs; (a) small area, (b) large area.
Figure 11. Schematic of continuous production of FRT-PSCs; (a) small area, (b) large area.
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Table 1. Summary of RT-PSCs based on solution process.
Table 1. Summary of RT-PSCs based on solution process.
Device StructureSolventRoom-Temperature ProcessPerformanceReferences
ITO/PEDOT:PSS/MAPbI3/PCBM/Ca/AlDMFDoping9.32%[33]
ITO/TiO2/MAPbI3/Spiro-OMeTAD/AgDMFVapor-assisted15.6%[36]
FTO/TiO2/MAPbI3/Spiro-OMeTAD/AgNMPAntisolvent immersing15.2%.[37]
FTO/c-TiO2/m-TiO2/FA0.5MA0.5PbI3/Spiro-OMeTAD/AgDMFDoping17.9%[32]
ITO/PEDOT:PSS/MAPbI3/PCBM/PDPIO/AlDMFVapor-assisted16.4%[38]
FTO/c-TiO2/m-TiO2/MAPbI3/Spiro-OMeTAD/AuDMAc/NMPAntisolvent rinsing17.09%[39]
FTO/c-TiO2/m-TiO2/FA0.8MA0.1Cs0.1PbI3/Spiro-OMeTAD/AgDMF/DMSOLigand exchange18.1%[40]
ITO/NiOx/MAPbI3/C60/Bis-C60/AgDMFLigand exchange17.1%[41]
FTO/c-TiO2/m-TiO2/MAPbI3/Spiro-OMeTAD/MnO3/AgTMENovel solvent20.02%[42]
ITO/SnO2/(FAPbI3)1(MAPbBr3)0.05/BABr-PEAI/Spiro-OMeTAD/AgDMF/DMSODoping19.09%[43]
FTO/c-TiOx/m-TiOx/MAPb(I1 − xClx)3/Spiro-OMeTAD/AuMA/EA/ACNNovel solvent22.32%[44]
ITO/NiOx/MAPb(I1 − xClx)3/PCBM/BCP/AgMA/EA/ACNNovel solvent23.07%[44]
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Wang, G.; Li, W.; Xu, H.; Song, Q. Low-Cost Room-Temperature Perovskite Solar Cells Suitable for Continuous Production. Electronics 2023, 12, 4498. https://doi.org/10.3390/electronics12214498

AMA Style

Wang G, Li W, Xu H, Song Q. Low-Cost Room-Temperature Perovskite Solar Cells Suitable for Continuous Production. Electronics. 2023; 12(21):4498. https://doi.org/10.3390/electronics12214498

Chicago/Turabian Style

Wang, Gang, Weikui Li, Hang Xu, and Qunliang Song. 2023. "Low-Cost Room-Temperature Perovskite Solar Cells Suitable for Continuous Production" Electronics 12, no. 21: 4498. https://doi.org/10.3390/electronics12214498

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