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Review

Advances in Charge Carrier Mobility of Diketopyrrolopyrrole-Based Organic Semiconductors

by
Zhengran He
1,*,
Kyeiwaa Asare-Yeboah
1 and
Sheng Bi
2,*
1
Department of Electrical and Computer Engineering, Penn State University Behrend, Erie, PA 16563, USA
2
Key Laboratory for Precision and Non-Traditional Machining Technology of the Ministry of Education, Dalian University of Technology, Dalian 116024, China
*
Authors to whom correspondence should be addressed.
Coatings 2024, 14(9), 1080; https://doi.org/10.3390/coatings14091080
Submission received: 19 July 2024 / Revised: 15 August 2024 / Accepted: 21 August 2024 / Published: 23 August 2024
(This article belongs to the Section Thin Films)
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Versions Notes

Abstract

:
In recent years, the charge carrier mobility study of organic semiconductors has seen significant progress and surpassed that of amorphous silicon thanks to the development of various molecular engineering, solution processing, and external alignment methods. These advances have allowed the implementation of organic semiconductors for fabricating high-performance organic electronic devices. In particular, diketopyrrolopyrrole-based small-molecular and polymeric organic semiconductors have garnered considerable research interest due to their ambipolar charge-carrier properties. In this article, we focus on conducting a comprehensive review of previous studies that are dedicated to the external alignment, thermal annealing, and molecular engineering of diketopyrrolopyrrole molecular structures and side-chain structures in order to achieve oriented crystal orientation, optimized thin-film morphology, and enhanced charge carrier transport. By discussing these benchmark studies, this work aims to provide general insights into optimizing other high-mobility, solution-processed organic semiconductors and sheds lights on realizing the acceleration of organic electronic device applications.

1. Background and Challenges

1.1. Advances in Charge Carrier Mobilities

In recent years, research in the charge carrier transport of solution-processed organic semiconductors has advanced at an exponential rate, allowing the mobilities to facilely surpass those of amorphous silicon [1,2,3,4,5,6,7,8]. For example, Tazuhara and colleagues documented the growth of 2,7-didodecyl[1]benzothieno[3,2-b][1]benzothiophene (C12-BTBT) organic crystals with extensive polycrystalline domains using a binary toluene/mesitylene solvent approach, which generated a mobility of 10 cm2/Vs [9]. Tripathi et al. reported the ambipolar charge transport in a 9,10-diphenylanthracene (DPA) organic semiconductor, which comprises phenyl groups at the anthracene backbone positions [10]. The DPA bulk crystals showed an electron mobility of 13 cm2/Vs, as well as a lower hole mobility of 3.7 cm2/Vs, which at a high-temperature regime featured bandlike transport behavior. Xue et al. reported a method of removing polar solvent residues in order to enhance the mobility of 6,13-bis(triisopropylsilylethynyl)-5,7,12,14-tetraazapentacene (TIPS-TAP) [11]. After the polar solvent residues were removed, the TIPS-TAP crystal ribbons with an alignment of several hundred micrometers demonstrated a 60% improvement in mobility with an electron mobility of up to 13.3 cm2/Vs. He et al. reported the solution-based self-assembly of dihexyl-substituted DBTDT (C6-DBTDT) organic crystals with two different phases [12]. Drop-casting C6-DBTDT in a concentrated chlorobenzene solution resulted in platelet-like single crystals with an α-phase, whereas a diluted solution yielded microribbon-like single crystals with a β-phase, giving rise to mobilities of 8.5 cm2/Vs and 18.9 cm2/Vs, respectively. Jurchescu et al. reported the incorporation of 6,13-pentacenequinone (PQ) as a gate dielectric material to improve the single-crystal charge transport of pentacene [13]. The interface-scattering centers of the PQ dielectric layer led to a high-quality interface and yielded a hole mobility of 40 cm2/Vs.

1.2. Advances in Organic Electronic Device Applications

The elevated charge carrier mobilities have further sparked research interest in developing high-performance organic semiconductor devices, including organic gas sensors, photodetectors, and complementary inverters. In this section, we briefly discuss those device applications in order to shed light on opening up the avenue to realizing high-efficiency flexible electronics.
Lee et al. reported the detection of ammonia gas molecules by fabricating a 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS pentacene)-based gas sensor. The enhanced rate of ammonia gas adsorption to the TIPS pentacene film surface allowed the electrons to react with the semiconductor hole charge carriers and reduced the overall positive charge, giving rise to the capability of detecting an even lower gas concentration [14]. Hou et al. reported the detection of nitrogen dioxide gas by using a TIPS pentacene-based gas sensor. The enhanced density of the grain boundaries as a result of annealing TIPS pentacene with solvent vapors improved the NO2 gas adsorption and improved the gas sensor responsivity by an order of magnitude [15]. Benavides et al. reported TIPS pentacene was demonstrated as an interlayer in a poly-3-hexyl-thiophene(P3HT)/[6, 6]-phenyl C61 butyric acid methyl ester heterojunction configuration in order to reduce the dark current of the photodetectors [16]. The insertion of the TIPS pentacene interlayer significantly enhanced the photodetector performance by elevating the device’s dynamic range and increasing the photodetector detectivity of green light irradiation. Zhao et al. reported C60 and TIPS pentacene single crystals with both excellent electron and hole mobility were employed in fabricating highly sensitive photodetectors [17]. The absorption of C60 and TIPS pentacene single crystals gave rise to excellent responsivities, ranging from ultraviolet light to the near-infrared light. Jea et al. reported successive deposition of TIPS pentacene and F16CuPc microarrays with alternating directional p-channels and n-channels [18]. The transistor devices fabricated by using this method revealed ambipolar charge transport characteristics, which were applied in air-stable complementary inverters. Janneck et al. reported a zone-casting method to fabricate highly crystalline 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT)-based long-channel transistors with 7.5 cm2/V mobility and integrated them into inverters [19]. The inverter device comprised a 19-stage ring oscillator and showed gains up to 40 and an operating frequency of 630 Hz.

1.3. Current Challenges in Organic Electronics

Despite these aforementioned advances, the in-solution processing of both small-molecular and polymeric organic semiconductors has met ongoing challenges, which has impeded applications in high-performance flexible electronics [20,21,22,23,24]. Here, we will briefly discuss each of these challenges, including nonuniform morphology, low crystallinity, and nonoptimal molecular packing [25,26,27,28,29,30]. First of all, nonuniform morphology features crystal misorientation, inferior substrate coverage, and grain-width variations. Crystal misorientation arises from drop-casting organic semiconductor solution and the substrate anisotropic crystal growth behavior [31,32,33,34,35,36,37]. For instance, several studies have reported that drop-casting organic semiconductors, such as TIPS pentacene and 5,6,11,12-Tetrachlorotetracene, caused the crystal to grow in anisotropic directions [38,39,40,41,42,43]. When those misoriented crystals were manipulated as the device active layer of thin-film transistors, such misoriented crystals could further induce anisotropic mobilities [44,45,46,47]. A previous report indicated that the mobilities measured from randomly aligned TIPS pentacene organic crystals can vary by one order of magnitude [48]. Such mobility variation can be further exaggerated to three to four orders of magnitude based on the different crystal coverage in the charge transport channel [49]. Those dramatic mobility variations have made it challenging to apply these organic semiconductors for fabricating high-performance organic electronic devices. For these reasons, it becomes highly desirable to apply alignment methods to externally confine the direction in which the organic semiconductors may crystallize. Those external force alignment methods include substrate patterning-based methods [50,51,52,53,54,55,56], solution shearing-based methods [57,58,59], capillary force-based methods [60,61,62], and so on.
Thin films for organic semiconductors are typically produced using various techniques such as spin-coating [63,64,65,66], drop-casting [67,68,69], and spray-coating [70,71,72,73]. Each of these methods offers unique advantages and disadvantages depending on the desired film morphology, uniformity, and thickness control. Spin-coating is widely used for its ability to produce uniform thin films with controlled thickness, but it often results in low crystallinity due to rapid solvent evaporation. Drop-casting, on the other hand, allows for better crystallinity but can lead to nonuniform film morphology with significant variations in grain size. Spray-coating provides a scalable approach for large-area coatings, though it can be challenging to achieve uniform film thickness and high crystallinity. Table 1 summarizes the key characteristics of these methods. Consequently, post-thermal annealing or solvent annealing is typically applied to spin-coated organic semiconductor films in order to increase the crystallinity of the semiconductor film and to enhance the charge carrier mobilities [74,75,76,77,78].
Table 1 lists each method used for depositing organic semiconductors discussed in this section, with their advantages and disadvantages.
Furthermore, nonoptimal molecular packing has been an issue that obstructs the electrical charge transport of organic semiconductors. Thus, side-chain engineering has become an effective method to improve the molecular packing of organic semiconductors. Various studies have reported miscellaneous molecular engineering and side-chain modifications which give rise to high-mobility organic semiconductors. For instance, miscellaneous small-molecular and polymeric organic semiconductors have been developed based on diketopyrrolopyrrole (DPP)-based material by side-chain engineering, yielding a mobility close to 10 cm2/Vs [79,80,81]. Small-molecular 6,13-bis(triisopropylsilylethynyl) TIPS pentacene is an organic semiconductor developed upon its predecessor pentacene as a soluble counterpart in organic solvents [38,82]. The bulky alkyl side-chain engineering allows TIPS pentacene to interrupt the herringbone packing motif and thereby to exhibit improved solubility in organic solvents [83,84,85]. The enhanced π–π stacking in TIPS pentacene favors charge transport and leads to hole mobilities over 10 cm2/Vs [86]. C8-BTBT is an organic polymeric semiconductor incorporating the [1]benzothieno[3,2-b][1]-benzothiophene unit as the base material, which has been showcased with mobilities reaching over 40 cm2/Vs [87].
Given the importance of these benchmark organic semiconducting small molecules and polymers, various review articles [88,89,90,91,92,93,94,95,96] have recently come to light that summarize the tremendous efforts dedicated to addressing these aforementioned challenges of employing TIPS pentacene and C8-BTBT for fabricating thin-film transistors. Nevertheless, a detailed review of implementing diketopyrrolopyrrole in fabricating thin-film transistors has not been reported yet. In this article, we will conduct a comprehensive review of the various works dedicated to the solution processing, crystal growth, external alignment, molecular engineering, and charge transport properties of the diketopyrrolopyrrole-based small-molecular and polymeric organic semiconductors. In particular, we will review these works in the categories of external alignment, thermal annealing, and molecular engineering. Figure 1 shows the molecular structures of diketopyrrolopyrrole-based small-molecular and polymeric organic semiconductors reviewed in our article. By investigating these examples, we shed light on the importance of optimizing semiconductor crystallization, film morphology, crystal alignment, and ambipolar behavior in order to maximize the charge transport property of diketopyrrolopyrrole-based organic semiconductors.

2. Review of Diketopyrrolopyrrole-Based Organic Semiconductors

2.1. Properties of Diketopyrrolopyrrole-Based Organic Semiconductors

Diketopyrrolopyrrole-based pigments have been reported with various colors that ranged from red to blue [97,98,99,100,101]. The synthesis of diketopyrrolopyrrole pigment was first reported by Parnum et al. in a pivotal study in 1974. The flanking with two phenyl units led to an insoluble hydrocarbon pentalene-based molecule with an 8-π electron-fused ring [102]. Iqbal et al. developed diketopyrrolopyrrole dyes and pigments and improved the yield by demonstrating a single reaction process between dialkyl succinate and aromatic nitrile [103]. Following these studies, diketopyrrolopyrrole derivatives with various side-chain engineering and functionalizations have been reported with more varieties of colors [80,104]. For instance, diketopyrrolopyrrole flanked with side chains exhibits modified planarity, π–π stacking distance, energy states, and charge transport properties. In particular, these properties make diketopyrrolopyrrole attractive for miscellaneous organic electronic devices, including organic sensors, solar cells, and thin-film transistors. Therefore, in diketopyrrolopyrrole-based semiconductors, π–π interactions and molecular aggregation significantly influence electron and hole mobility. The planarity of the diketopyrrolopyrrole core, facilitated by these π–π interactions, enhances charge transport by promoting efficient stacking, which in turn decreases the π–π stacking distance [105,106,107]. Molecular aggregation further contributes to charge transport by increasing crystallinity and order in the film. The side-chain modifications include varying the length and branching of alkyl chains. These modifications affect the molecular packing, which quantitatively influences the π–π stacking distance and thus the charge transport properties.
Diketopyrrolopyrrole-based materials have garnered significant attention for their tunable bandgaps and energy levels, which are critical for optimizing device performance in organic field-effect transistors (OFETs) [108,109,110,111,112,113] and organic photovoltaics (OPVs) [114,115,116,117,118]. The bandgap of diketopyrrolopyrrole-based polymers typically ranges between 1.5 and 2.0 eV, making them suitable for absorbing visible light, a crucial characteristic for OPV applications. The energy levels, including the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), are finely tuned through side-chain engineering and donor–acceptor molecular design, enabling efficient charge separation and transport. Density functional theory (DFT) modeling has provided insights into the charge transfer mechanisms at the molecular level, revealing that the donor–acceptor interactions significantly enhance charge delocalization and mobility [101,119]. These theoretical models are crucial for understanding the molecular origins of the high-performance characteristics observed in DPP-based devices.
Additionally, the transition from laboratory-scale synthesis to pilot-scale and industrial-scale production of diketopyrrolopyrrole-based conjugated materials presents several challenges, including scalability, cost-effectiveness, and material purity. Diketopyrrolopyrrole, isoDPP, and their derivatives require precise synthetic routes that can be difficult to replicate on a larger scale [120,121,122]. Recent advances in continuous flow chemistry and scalable polymerization techniques have begun to address these challenges, enabling the production of high-purity diketopyrrolopyrrole-based materials with consistent properties. However, further development is needed to optimize these processes for industrial-scale production. Challenges such as the handling of reactive intermediates, the control of molecular weight distribution, and the minimization of by-products must be overcome to ensure that diketopyrrolopyrrole-based materials can be produced at scale while maintaining their high performance in electronic applications. These advancements are critical for the widespread adoption of diketopyrrolopyrrole-based materials in commercial electronics and photovoltaic devices.
Furthermore, while diketopyrrolopyrrole-based organic semiconductors have demonstrated significant advancements in charge carrier mobility and have been widely explored for applications in organic electronics, it is essential to contextualize these developments within the broader landscape of semiconductor materials. Inorganic semiconductors such as Fe2O3, Cu2O, and CeO2 have long been established in the field due to their robust thermal stability, high carrier mobility, and suitability for high-temperature applications, and they also rely on thermal treatments to stabilize their crystalline phases and optimize their electronic properties [123,124,125,126]. However, they often lack the flexibility, tunability, and solution-processability that organic materials offer. Diketopyrrolopyrrole-based materials, with their tunable electronic properties through side-chain engineering and molecular design, present unique advantages in applications requiring lightweight, flexible, and solution-processable devices. Yet, challenges such as stability, environmental impact, and manufacturability need to be addressed.
A comprehensive understanding of photon-excited charge-carrier mechanisms, photo-redox processes, plasmonic effects, and dielectric properties is critical for optimizing the performance of diketopyrrolopyrrole-based materials in applications such as photodetectors and gas sensors [127,128,129,130,131,132,133,134,135,136]. When diketopyrrolopyrrole-based semiconductors absorb photons, they generate electron–hole pairs that are vital for initiating photocatalytic reactions. The efficiency of charge separation and the subsequent electron transfer to surface-adsorbed species play a significant role in determining the material’s photocatalytic activity. Compared to inorganic semiconductors like Fe2O3, Cu2O, and CeO2, which are known for their strong charge carrier mobilities and stable performance [137,138,139], diketopyrrolopyrrole-based materials offer the advantage of molecular tunability, which can optimize light absorption and charge carrier dynamics. However, the intrinsic stability of diketopyrrolopyrrole-based materials is a concern that must be addressed to enhance their long-term performance. Further research into hybrid organic–inorganic systems and the incorporation of plasmonic nanoparticles could unlock new opportunities to enhance the efficiency, stability, and applicability of diketopyrrolopyrrole-based semiconductors. Addressing these challenges while leveraging the strengths of diketopyrrolopyrrole-based semiconductors could pave the way for their broader application in the industry [140,141,142].
Bürgi et al. reported a thiophene-flanked diketopyrrolopyrrole polymer with ambipolar charge transport properties. The ambipolar transistor device showed an electron and hole mobility of 0.1 cm2/Vs and 0.09 cm2/Vs, respectively [143]. Diketopyrrolopyrrole pigments are usually composed of a diketopyrrolopyrrole core and flanked aromatic groups. The diketopyrrolopyrrole core has amine units and bicyclic carbonyl groups, and this can provide strong electron deficiency to the diketopyrrolopyrrole pigments. This property can be useful for donor acceptor conjugated semiconductor construction. DPP-based semiconductors showcase intensive π–π interactions and molecular aggregation, which is promising for being applied in organic electronic devices. The molecular design of thiophene-flanked DPP polymers plays a crucial role in balancing electron and hole mobilities. The incorporation of electron-deficient and electron-rich segments within the polymer backbone influences this balance. Critical factors affecting the balance include the energy level alignment, molecular packing, and film morphology. The design strategy of combining strong donor and acceptor units ensures that both types of charge carriers are effectively transported, resulting in ambipolar characteristics with balanced mobilities.

2.2. External Alignment of Diketopyrrolopyrrole-Based Organic Semiconductors

Bi et al. reported a double-solvent approach to control the crystal growth, as well as a “controlled evaporative self-assembly” (CESA) method to realize the alignment of 2,5-di-(2-ethylhexyl)-3,6-bis(5″-n-hexyl-2,2′,5′,2″]terthiophen-5-yl)-pyrrolo[3,4-c] pyrrole-1,4-dione (SMDPPEH) [144]. The underlying mechanism involves the balance between nucleation density and crystal growth, where an optimal concentration facilitates uniform crystal formation and alignment. With SMDPPEH casted in chloroform, the organic semiconductor material formed a few microcrystals that randomly scattered over the substrate (Figure 2a). When chloroform and ethanol were employed as the double solvents (chloroform/ethanol at a ratio of 15:1, 10:1, 5:1, and 1:1), an enhanced density of crystals was formed, although the crystals still lacked alignment and long-range uniformity (Figure 2b). When the CESA method was applied to control the SMDPPEH crystallization, it created a capillary force that guided the oriented growth of the organic semiconductor. The resultant enhanced morphology is shown in Figure 2c–f. The optimization of double solvents and simultaneous application of the CESA method led to the excellent alignment of CESA organic crystals. In addition, the grain width was noted to depend on the double-solvent ratio. In particular, a 5:1 ratio of chloroform/ethanol double solvents led to an optimized amount of nucleation seeds and density, and simultaneously the CESA method was noted to most effectively orient the organic crystal orientations of SMDPPEH and contributed to an enhanced mobility of 0.016 cm2/Vs. Therefore, a chloroform/ethanol ratio of 5:1 was found to be optimal for inducing nucleation and enhancing crystal density without compromising alignment. This ratio was crucial as it balanced the solvent evaporation rate, facilitating better control over crystal growth and alignment.
Besides the application of the CESA alignment and binary solvent method, Bi et al. also reported the mixing of SMDPPEH with P3HT to modulate its crystallization and morphology [145]. SMDPPEH was mixed with P3HT in a single solvent of chloroform at a weight ratio of 5:1, and the mixed solution was drop-casted on the substrate at various concentrations. The resultant morphologies of the SMDPPEH crystals are shown in Figure 3a–c as a function of different concentrations. At 1 mg/mL, the SMDPPEH crystals showed dash points (Figure 3a), implying such low concentration is insufficient for the semiconductor to continuously crystallize. When the concentration increases to 2 mg/mL, the SMDPPEH semiconductor formed well-aligned crystals with enhanced connection in the long range, as shown in Figure 3b. As the concentration further increases to 5 mg/mL, the morphology quickly deteriorated and many grain boundaries with crystalline defects populated (Figure 3c). The dependence of the SMDPPEH morphology on the solution concentration, as observed from the polarized microscopic optical images, is further confirmed by using scanning electron microscopy (Figure 3d–f). A mobility of 0.001 cm2/Vs was measured from the SMDPPEH/P3HT thin-film transistors based on the optimized concentration of 2 mg/mL.
Shin et al. reported a “template-guided solution-shearing (TGSS)” method to grow well-aligned π-extended donor–acceptor diketopyrrolopyrrole-based conjugated polymers, i.e., PTDPP-DTTE [79]. PTDPP-DTTE is composed of dithienyl-diketopyrrolopyrrole (TDPP) as the acceptor monomer and di(thienothienyl)ethylene (DTTE) as the donor monomer. The PTDPP-DTTE was deposited by using different methods, including the spin-coating, solution-shearing, and TGSS methods. As compared to the spin-coated film, the counterpart based on solution shearing showed alignment of polymer chains and elongated domains towards the shearing direction. In contrast, the crystals based on the TGSS method showed enhanced alignment of polymer chains, favorable for charge transport. GI-XRD results showed that the π–π stacking distance of the PTDPP-DTTE polymer was reduced to 3.47 Å when prepared by the TGSS method, as compared to 3.67 Å when deposited by spin-coating, indicating the micro-patterned mold results in larger strain between the PTDPP-DTTE polymer chains. Top-contact, bottom-gate transistors yielded a hole mobility of 3.13 cm2/Vs, 4.77 cm2/Vs, and 7.43 cm2/Vs, based on the deposition method of spin-coating, solution shearing, and the TGSS method, respectively. The TGSS method significantly enhances polymer alignment and charge transport by reducing the π–π stacking distance and improving molecular packing. This method is scalable for large-area organic electronics, as demonstrated by the uniformity of the films produced in our study. However, challenges such as maintaining uniform crystal orientation across larger substrates and controlling the shear rate and solvent evaporation uniformly must be addressed to ensure consistent performance across large areas.
The different studies reviewed in this section are summarized in Table 2.

2.3. Thermal Annealing of Diketopyrrolopyrrole-Based Organic Semiconductors

The thermal properties of diketopyrrolopyrrole-based organic semiconductors differ significantly from those of inorganic semiconductors. Thermal annealing in these materials primarily enhances structural order and crystallinity, which are crucial for charge transport.
Chen et al. reported ambipolar copolymer DPPT-TT based on diketopyrrolopyrrole and thieno[3,2-b]thiophene for thin-film transistor applications [146]. Transistors were fabricated based on a top-gate, bottom-contact configuration with poly(methyl methacrylate) (PMMA) as the gate dielectric layer. The effect of thermal annealing and the cleaning procedure of the gold electrodes was investigated on the charge transport of DPPT-TT semiconductors. Annealing at 320 °C reduces the electron-trapping impurities, decreases the contact resistance, and also improves the physical contact between the semiconductor and electrodes, which is favorable for charge transport. The optimal annealing temperature of 320 °C for DPPT-TT was determined based on its effect on reducing electron-trapping impurities, improving contact resistance, and enhancing physical contact between the semiconductor and electrodes. Thermal stability at this temperature ensures that the semiconductor maintains its performance by preserving the structural order and crystallinity. On the other hand, solvent cleaning of the gold electrodes prior to the deposition of DPPT-TT effectively modulates the gold work function to 4.7~4.9 eV, which facilitates electron injection. As a result, a1.36 ± 0.26 cm2/Vs (hole mobility) and 1.56 ± 0.49 cm2/Vs (electron mobility) were yielded from the DPPT-TT based on thermal annealing at 320 °C and the solvent cleaning of gold contact electrodes.
Nelson et al. studied film topography and charge transport of poly[2,5-dihexadecyl-3-5-[4-(2-hexyl-decyl)-4H-dithieno [3,2-b;2′, 3′-d] pyrrol-2-yl]-thiophen-2-yl-6-thiophen-2-yl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione] (PDDTP-DPP) [147]. The molecular structure of DPPTP-DPP as a donor–acceptor polymer is shown in Figure 1. The low bandgap PDDTP-DPP is composed of a strong donor DTP and a strong acceptor DPP. Transistors were made by patterning the gold source and drain electrodes with photolithography. OTS treatment was performed on the substrate before drop-casting the PDDTP-DPP polymer to form the active layer. The PDDTP-DPP film after thermal annealing exhibited mobilities correlated with the conducting channel length. In particular, a maximum hole mobility of 0.41 cm2/Vs was obtained based on 30 µm channel length. AFM imaging showed fine isotropic morphology composed of granular features rather than nanofibrillar morphology. Grazing incidence wide-angle X-ray scattering (GIWAXS) results indicated improved structural order after thermal annealing, responsible for the enhanced mobility.
Sonar et al. reported an ambipolar copolymer incorporating both a diketopyrrolopyrrole moiety and thiophene-benzothiadiazole-thiophene (TBT) as the donor–acceptor–donor building block [148]. The copolymer PDPP-TBT formed an active layer via spin coating, followed by thermal annealing. The AFM images of the PDPP-TBT films were presented in Figure 4a–d with different thermal annealing temperatures, including 120 °C, 180 °C, and 200 °C. While the PDPP-TBT film without annealing showed clustered nanofibers, these nanofibers increasingly prevail and form densely packed networks interconnecting the crystal domains as the thermal annealing temperature increases. Accordingly, the XRD spectra in Figure 4g showed enhanced peak intensities with increasing thermal annealing temperature. Thin-film transistors were fabricated by depositing the PDPP-TBT copolymers onto OTS-treated substrates and conducted with thermal annealing, yielding decent device performance in p- and n-channel modes, as shown in Figure 4e,f. The highest mobility values of 0.35 cm2/Vs (hole) and 0.4 cm2/Vs (electron) were obtained with thermal annealing at 200 °C.
Shahid et al. reported two selenophene-diketopyrrolopyrrole-based polymers, i.e., poly(3-(2,2′-biselenophen-5,5′-yl)-2,5-di(2-octyldodecyl)-6-(selenophen-2,5-yl)-1,4-diketopyrrolo[3,4-c]pyrrole (pDPPS3) and poly(3-(2,20-biselenophen-5,5′-yl)-2,5-di(2-octyldodecyl)-6-(thieno[3,2-b]thiophen-2,5-yl)-1,4-diketopyrrolo[3,4-c]pyrrole (pDPPS2TT), in an effort to lower the LUMO level in order to facilitate electron injection [149]. The synthesized pDPPS3 and pDPPS2TT polymers exhibit LUMO levels of 4 eV and 3.9 eV, respectively. After spin-coating the polymers onto HMDS-treated substrate, thermal annealing was found to play a vital role in enhancing the electrical charge transport, yielding a hole and electron mobility value of 0.1 cm2/Vs for pDPPS3, as well as hole and electron mobility values of 0.3 cm2/Vs and 0.05 cm2/Vs for pDPPS2TT. In comparison, enhanced hole and electron mobility values of 1.1 cm2/Vs and 0.15 cm2/Vs were showcased from pDPPS3. XRD results showed sharpened and intensified peak intensities for both polymers after thermal annealing, indicating enhanced crystallinity.
The different studies reviewed in this section are summarized in Table 3.

2.4. Molecular Engineering of Diketopyrrolopyrrole-Based Organic Semiconductors

Tang et al. reported three conjugated small-molecular semiconductors based on diketopyrrolopyrrole, which comprise a diketopyrrolopyrrole core [107]. These three small molecules, i.e., 2TzDPPA1-2DCV, 2TzDPPA2-2DCV, and 2TzDPPA3-2DCV, have the same branching location at the nitrogen atoms, as shown in Figure 1, but the alkyl side-chain differs in its length. In particular, side chains of 2-hexyldecyl, 2-octyldodecyl and 2-decyltetradecyl were attached to 2TzDPPA1-2DCV, 2TzDPPA2-2DCV, and 2TzDPPA3-2DCV, respectively. Side-chain length in 2TzDPPA derivatives plays a pivotal role in determining film morphology, molecular packing, and charge transport properties. Shorter side chains lead to more orderly packing and smoother film morphology, which enhances electron mobility. The key molecular design principles include optimizing side-chain length to balance crystallinity and film uniformity, thereby maximizing charge transport efficiency. AFM imaging results indicated that 2TzDPPA1-2DCV with a shorter side chain exhibited more uniform and continuous film topography. XRD implied that 2TzDPPA1-2DCV shows the largest d-spacing as a result of end-to-end packing, whereas 2TzDPPA3-2DCV shows the smallest d-spacing because of its interlaced packing between the alkyl side chain and the D diketopyrrolopyrrole PP core. After spin-coating the various diketopyrrolopyrrole-based small molecules onto octadecyltrimethoxysilane (OTS)-treated silicon dioxide to form an active layer, electrical characterization indicated an electron mobility of up to 0.28 cm2/Vs, 0.13 cm2/Vs, and 0.25 cm2/Vs for 2TzDPPA1-2DCV, 2TzDPPA2-2DCV, and 2TzDPPA3-2DCV, respectively.
Shin et al. reported four π-extended conjugated polymers based on thienothiophene-flanked diketopyrrolopyrrole (DPPTT) with different side chains, including 2-octyldodecyl (PDPPTT-T-10), 2-decyltetradecyl (PDPPTT-T-12), 2-tetradecylhexadecyl (PDPPTT-T-14), 2-hexadecyloctadecyl (PDPPTT-T-16), and 2-octadecyldocosyl (PDPPTT-T-18) [150]. Depositing those conjugated polymers onto OTS-treated substrate yielded p-type transistor behaviors for all types of semiconductors. The highest mobility values of 1.23 cm2/Vs, 0.16 cm2/Vs, 1.92 cm2/Vs, 0.35 cm2/Vs, and 0.14 cm2/Vs were obtained from PDPPTT-T-10, -12, -14, -16, and -18, respectively. The highest hole mobilities from PDPPTT-T-10 and -14 were attributed to the smooth surfaces with reduced roughness, as shown in Figure 5a–e. Additionally, the XRD spectra in Figure 5f,g show high crystallinity for PDPPTT-T-10 and -14, which adopt well-ordered lamellar structures with a dominant edge-on orientation (Figure 5h). In particular, the PDPPTT-T-14 film exhibited the smallest π–π stacking distance out of all five conjugated polymers, which is responsible for its highest mobility.
Chen et al. reported two donor–acceptor copolymers, poly[2,5-bis(alkyl)pyrrolo[3,4-c]pyrrole-1,4(2H, 5H)-dione-alt-5,5′-di(thiophen-2-yl)-2,2′-(E)-2-(2-(thiophen-2-yl)vinyl) thiophene] (PDVTs), which are attached with two alkyl side chains with different lengths [80]. In particular, PDVT-8 has a short side chain of a 2-octyldodecyl group, whereas PDVT-10 has a longer side chain of a 2-decyltetradecyl group. With thermal annealing at 180 °C, the resultant thin-film topography is shown in Figure 6a–d. Both PDVT-8 and PDVT-10 films exhibit uniform intertwined fibers after spin-coating and enlarged polycrystalline grains with improved uniformity and interconnection after thermal annealing due to the intermolecular interactions between the copolymer backbones. Figure 6e,f show the grazing incidence out-of-plane and in-plane X-ray scattering of the PDVT-8 and PDVT-10 films after thermal annealing. Both films exhibit sharp (100) diffraction peaks with an edge-on packing structure. A π–π stacking distance of 3.72 Å and 3.66 Å was measured for PDVT-8 and PDVT-10. Transistors yielded a hole mobility of 4.5 cm2/Vs and 8.2 cm2/Vs for PDVT-8 and PDVT-10. The larger mobility of PDVT-10 is due to its enhanced topography uniformity and smaller π–π stacking distance. This study provides a detailed correlation between XRD data, AFM images, and transistor performance in PDVT-based copolymers. XRD analysis reveals the degree of crystallinity and π–π stacking distances, while AFM images illustrate the film morphology. These structural characteristics directly correlate with the measured transistor mobilities, highlighting the relationship between molecular packing, crystallinity, and device performance.
Yun et al. reported a copolymer poly[2,5-bis(2-octyldodecyl)pyrrolo[3,4-c] pyrrole-1,4(2H, 5H)-dione-(E)-[2,2′-bithiophen]-5-yl)-3-(thiophen-2-yl)acrylonitrile] (PDPP-CNTVT), which has an inclusion of a nitrile group in the polymer vinyl linkage, and compared its electrical performance with another diketopyrrolopyrrole-based copolymer (poly[2,5-bis(2-octyldodecyl) pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-(E)-1,2-di(2,2′-bithiophen-5-yl)ethene]) (PDPP-TVT) [81]. After spin-coating PDPP-CNTVT and PDPP-TVT onto prepatterned gold electrodes, depositing PMMA as gate dielectric layer and thermally evaporating Al as top-gate electrode, the transfer curves, as plotted in Figure 7a,b, show a dominant p-type behavior for PDPP-TVT and ambipolar behavior for PDPP-CNTVT. The device performance was further optimized by varying the solution concentration and modulating the active layer thickness. As shown in Figure 7c, reduction in the PDPP-CNTVT thickness results in a higher electron mobility of 7 cm2/Vs. The enhanced charge transport in a thinner PDPP-CNTVT layer was attributed to the lower contact resistance and lesser presence of electron trapping sites in the bulk active layer, as illustrated in Figure 7d.
The different studies reviewed in this section are summarized in Table 4.

2.5. Other Works on Diketopyrrolopyrrole-Based Organic Semiconductors

Kanimozhi et al. reported a conjugated copolymer, i.e., N-CS2DPP-OD-TEG, based on diketopyrrolopyrrole and diketopyrrolopyrrole (DPP-DPP) [151]. In this work, functionalized with triethylene glycol chains, the diketopyrrolopyrrole unit was then synthesized to form the high-molecular-weight copolymer DPP-DPP. For the bottom-gate transistors, a low balanced hole and electron mobility of ~0.01 cm2/Vs was obtained. In contrast, a much higher electron mobility of 3 cm2/Vs was demonstrated for the top-gate counterparts, which was attributed to the high-quality charge transport interface between the DPP-DPP organic semiconductor and the CYTOP gate dielectric layer.
Bronstein et al. prepared a polymer, namely P1, based on the copolymerization of both thieno[3,2-b]thiophene and diketopyrrolopyrrole [152]. Although ambipolar electrical performance of the devices was observed, a low electron mobility of 0.03 cm2/Vs, as well as a much higher hole mobility of up to 1.95 cm2/Vs, was reported from the thin-film transistors without employing thermal annealing at a high temperature. In addition, heterojunction solar cells incorporating the polymer and PC71BM exhibited an energy efficiency of 5.4%. This study shows that interface engineering is critical in optimizing the interaction between the semiconductor and dielectric layers, directly influencing device performance. For polymers such as P1 with low electron mobility, strategies such as modifying the dielectric interface, using interfacial layers, or adjusting the work function of electrodes can enhance electron mobility while maintaining or improving hole mobility.
Wang et al. reported an ambipolar copolymer poly(diketopyrrolopyrrole-terthiophene) (PDPPHD-T3) based on hexyldecyl-substituted diketopyrrolopyrrole and thiophene for application in xylene sensors [153]. In this work, a diketopyrrolopyrrole block was attached with a long alkyl chain to enhance the solution processability of the polymer. Transistors based on the PDPPHD-T3 copolymer and OTS-treated substrate showed a hole and electron mobility of 0.125 cm2/Vs and 0.027 cm2/Vs, respectively. Exposure to xylene vapors increased HOMO and LUMO levels of the PDPPHD-T3 polymer. Such energy level changes reduced the barrier for hole injection but increased that for electron injection, which modulated the electrical behaviors of the PDPPHD-T3-based thin-film transistor. As a result, the PDPPHD-T3 transistor-based sensor showed capability for detecting xylene at 40 ppm. This study shows PDPPHD-T3 polymer exhibits promising sensitivity and selectivity for xylene detection, with a response time that compares favorably to existing sensors. These results indicate that the sensor can detect xylene concentrations as low as 40 ppm, with rapid response and recovery times. The sensitivity is attributed to the modulation of energy levels upon xylene exposure, which influences the charge transport properties.
Li et al. reported a donor–acceptor polymeric organic semiconductor PDQT which comprises diketopyrrolopyrrole and β-unsubstituted quaterthiophene (QT) [78]. Without applying thermal annealing, PDQT forms layer-by-layer lamellar crystalline structures. The strong intermolecular interactions between the diketopyrrolopyrrole moieties, as well as the those between the DPP-QT donor–acceptor, induce the polymer chains to spontaneously form self-assembled structures of close proximity with a large π–π overlap. These interconnected crystalline structures provide an efficient intergranular charge transport pathway. The effect from thermal annealing and molecular weight on the thin-film topography was studied by using AFM (Figure 8a–f). The PDQT polymer morphology was observed to depend on its molecular weight. For PDQT with a high molecular weight, densely packed grains were formed with nanometer size, whereas for the counterpart with a low molecular weight, the film was found to be present with pinholes that deteriorate the interconnected structure. Transistors were fabricated by depositing the PDQT polymer onto OTS-treated substrates, which yielded p-type electrical behaviors, as shown in the output and transfer curves in Figure 8g–j. A mobility of 0.89 cm2/Vs was obtained from the high-molecular-weight PDQT-based thin-film transistors, which further increased to 0.97 cm2/Vs when the crystalline film was thermally annealed at 100 °C. In contrast, the low-molecular-weight PDQT-based devices fabricated using the same conditions exhibited only a lower mobility of 0.35–0.39 cm2/Vs.
The different studies reviewed in this section are summarized in Table 5.

3. Conclusions and Outlook

In this article, we have reported a comprehensive review of the various efforts dedicated to achieving uniform crystal orientation, improving film morphology, and optimizing the charge carrier transport of small-molecular and polymeric organic semiconductors based on diketopyrrolopyrrole. First of all, external alignment contributes to aligned crystal orientations, controlled crystal growth, and improved charge carrier transport. Additionally, thermal annealing plays a vital role in modulating the ambipolar behaviors, enhanced structural order, film morphology, and semiconductor crystallinity. Furthermore, side-chain engineering results in enhanced π–π stacking distance, more orderly packing, improved crystallinity, enhanced topography, greater surface uniformity, and elevated mobility. By discussing the category of external crystal alignment, thermal annealing, and molecular engineering of diketopyrrolopyrrole-based organic semiconductors, this work demonstrates that these universal methods can be applied to other solution-processed organic semiconductors to improve their molecular packing, enhance film morphology and crystallinity, and boost charge transport properties.
Future works in the following fields will yield more exciting outcomes in the research of organic semiconductors and organic electronic devices. First, since small-molecular and polymeric organic semiconductors based on diketopyrrolopyrrole exhibit ambipolar behaviors, these attributes can find extensive applications in complimentary inverters and thereby open up exciting pathways for high-performance organic electronics. Second, in addition to the polymeric additives such as P3HT, other additives, including small-molecular additives [154,155,156,157,158] and nanostructured additives [159,160,161,162,163,164], have been documented to manipulate the nucleation seed deposition, crystal formation, and film morphology of other organic semiconductors such as TIPS pentacene. Mixing these small-molecular and nanostructured additives with diketopyrrolopyrrole-based organic semiconductors, therefore, will enable the tuning of nucleation, crystallization, and charge transport. Furthermore, it is well known that external force [165,166,167,168,169,170] contributes to rigid alignment of the organic crystals, whereas polymeric additives result in overall morphological uniformity. Therefore, it can be beneficial to combine external force alignment methods with polymeric additives [171,172,173,174,175,176,177,178] to control the crystallization and charge transport of diketopyrrolopyrrole-based semiconductors. We believe future endeavors in these aforementioned fields will unveil a promising roadmap to realizing high-performance organic electronics applications.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

No new data were created or analyzed in this study.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. The molecular structures of various small-molecular and polymeric semiconductors based on diketopyrrolopyrrole that are reviewed in this article.
Figure 1. The molecular structures of various small-molecular and polymeric semiconductors based on diketopyrrolopyrrole that are reviewed in this article.
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Figure 2. Optical images of SMDPPEH microcrystals obtained from drop-casting in various solvents, including (a) chloroform and chloroform/ethanol at the ratio of (b) 5:1, (c) 15:1, (d) 10:1, (e) 5:1, and (f) 1:1. CESA method was applied to orient and control the SMDPPEH crystals in (c–f). Images (a,b) have the same scale bar of 100 µm, as in (a), whereas images in (c–f) have the identical scale bar of 100 µm, as in (c). Reproduced from reference [144] with permission from American Institute of Physics.
Figure 2. Optical images of SMDPPEH microcrystals obtained from drop-casting in various solvents, including (a) chloroform and chloroform/ethanol at the ratio of (b) 5:1, (c) 15:1, (d) 10:1, (e) 5:1, and (f) 1:1. CESA method was applied to orient and control the SMDPPEH crystals in (c–f). Images (a,b) have the same scale bar of 100 µm, as in (a), whereas images in (c–f) have the identical scale bar of 100 µm, as in (c). Reproduced from reference [144] with permission from American Institute of Physics.
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Figure 3. Optical images of SMDPPEH crystals with the P3HT additive at a 5:1 weight ratio based on different concentrations, including (a) 1, (b) 2, and (c) 5 mg/mL. The SEM images based on the same weight ratio and concentration as in (a–c) are shown in (d–f). Reproduced from reference [145] with permission from Elsevier.
Figure 3. Optical images of SMDPPEH crystals with the P3HT additive at a 5:1 weight ratio based on different concentrations, including (a) 1, (b) 2, and (c) 5 mg/mL. The SEM images based on the same weight ratio and concentration as in (a–c) are shown in (d–f). Reproduced from reference [145] with permission from Elsevier.
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Figure 4. AFM images showing the PDPP-TBT after thermal annealing at (a) room temperature, (b) 120 °C, (c) 180 °C, and (d) 200 °C. (e,f) show the output characteristics for the p- and n-channel modes, respectively. The thermal annealing was conducted at 200 °C. (g) XRD spectra of the PDPP-TBT thin films with different annealing temperatures. Reproduced from reference [148] with permission from Wiley.
Figure 4. AFM images showing the PDPP-TBT after thermal annealing at (a) room temperature, (b) 120 °C, (c) 180 °C, and (d) 200 °C. (e,f) show the output characteristics for the p- and n-channel modes, respectively. The thermal annealing was conducted at 200 °C. (g) XRD spectra of the PDPP-TBT thin films with different annealing temperatures. Reproduced from reference [148] with permission from Wiley.
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Figure 5. AFM height images the various conjugated polymers, including (a) PDPPTT-T-10, (b) -12, (c) -14, (d) -16, and (e) -18. (f) Out-of-plane and (g) in-plane XRD spectra of the conjugated polymers. (h) A schematic drawing showing the transition of molecular packing from PDPPTT-T-10 to -18 as respective to the substrates. Reproduced from reference [150] with permission from ACS Publications.
Figure 5. AFM height images the various conjugated polymers, including (a) PDPPTT-T-10, (b) -12, (c) -14, (d) -16, and (e) -18. (f) Out-of-plane and (g) in-plane XRD spectra of the conjugated polymers. (h) A schematic drawing showing the transition of molecular packing from PDPPTT-T-10 to -18 as respective to the substrates. Reproduced from reference [150] with permission from ACS Publications.
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Figure 6. AFM topography images of (a,b) PDVT-8 and (c,d) PDVT-10 polymer films. (a,c) are based on no annealing, whereas (b,d) are based on annealing at 180 °C. (e) Grazing incidence out-of-plane X-ray scattering and (f) in-plane X-ray scattering based on annealing at 180 °C. Reproduced from reference [80] with permission from Wiley.
Figure 6. AFM topography images of (a,b) PDVT-8 and (c,d) PDVT-10 polymer films. (a,c) are based on no annealing, whereas (b,d) are based on annealing at 180 °C. (e) Grazing incidence out-of-plane X-ray scattering and (f) in-plane X-ray scattering based on annealing at 180 °C. Reproduced from reference [80] with permission from Wiley.
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Figure 7. Ambipolar transfer curves of bottom-contact transistors based on (a) PDPP-TVT with annealing at 200 °C and (b) PDPP-CNTVT with annealing at 310 °C. The blue curves in (a,b) correspond to the square root of the drain current, while the red curves correspond to the drain current. The two arrows in the right figure of (b) indicate the presence of hysteresis in the transfer characteristics. (c) Correlation between the extracted charge-carrier mobilities, solution concentration, and active layer thickness of PDPP-CNTVT. (d) A schematic plot illustrating the transport and trapping of electron charge carriers in two different cases with different active layer thicknesses. Reproduced from reference [81] with permission from Wiley.
Figure 7. Ambipolar transfer curves of bottom-contact transistors based on (a) PDPP-TVT with annealing at 200 °C and (b) PDPP-CNTVT with annealing at 310 °C. The blue curves in (a,b) correspond to the square root of the drain current, while the red curves correspond to the drain current. The two arrows in the right figure of (b) indicate the presence of hysteresis in the transfer characteristics. (c) Correlation between the extracted charge-carrier mobilities, solution concentration, and active layer thickness of PDPP-CNTVT. (d) A schematic plot illustrating the transport and trapping of electron charge carriers in two different cases with different active layer thicknesses. Reproduced from reference [81] with permission from Wiley.
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Figure 8. AFM height images showing (a,d) high-molecular-weight PDQT film, (b,e) high-molecular-weight PDQT film annealed at100 °C, and (c,f) low-molecular-weight PDQT thin film annealed at 100 °C. Output and transfer characteristics of high-molecular-weight PDQT-based thin-film transistors (g,h) without thermal annealing and (i,j) annealed at 100 °C. Reproduced from reference [78] with permission from ACS Publications.
Figure 8. AFM height images showing (a,d) high-molecular-weight PDQT film, (b,e) high-molecular-weight PDQT film annealed at100 °C, and (c,f) low-molecular-weight PDQT thin film annealed at 100 °C. Output and transfer characteristics of high-molecular-weight PDQT-based thin-film transistors (g,h) without thermal annealing and (i,j) annealed at 100 °C. Reproduced from reference [78] with permission from ACS Publications.
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Table 1. A list of each method typically used for depositing organic semiconductors, as well as the advantages and disadvantages of each method.
Table 1. A list of each method typically used for depositing organic semiconductors, as well as the advantages and disadvantages of each method.
MethodAdvantagesDisadvantages
Spin-CoatingUniform film thickness, easy to controlLow crystallinity, limited to small areas
Drop-CastingHigh crystallinity, simple equipmentNonuniform morphology, grain size variation
Spray-CoatingScalable for large areas, suitable for flexible substratesChallenging thickness control, lower crystallinity
Table 2. Summary of the different works reviewed in this section, including the diketopyrrolopyrrole-based semiconductors, p-type or n-type, the result findings, and mobility.
Table 2. Summary of the different works reviewed in this section, including the diketopyrrolopyrrole-based semiconductors, p-type or n-type, the result findings, and mobility.
AuthorSemiconductorTypeResult FindingsMobility
Bi et al. [144]SMDPPEHp-typeA “controlled evaporative self-assembly” method aligned crystal orientations0.016 cm2/Vs
Bi et al. [145]SMDPPEHp-typeP3HT was used as a polymer additive to modulate morphology and alignment0.001 cm2/Vs
Shin et al. [79]PTDPP-DTTEp-typeA “template-guided solution-shearing” method oriented crystals7.43 cm2/Vs based on the TGSS method
Table 3. Summary of the different works reviewed in this section, including the diketopyrrolopyrrole-based semiconductors, p-type or n-type, the result findings, and mobility.
Table 3. Summary of the different works reviewed in this section, including the diketopyrrolopyrrole-based semiconductors, p-type or n-type, the result findings, and mobility.
AuthorSemiconductorTypeResult FindingsMobility
Chen et al. [146]DPPT-TTAmbipolarThermal annealing and cleaning procedure of gold contacts impact the ambipolar behaviors of DPP-TT1.36 ± 0.26 cm2/Vs (hole) and 1.56 ± 0.49 cm2/Vs (electron)
Nelson et al. [147]PDDTP-DPPp-typeThermal annealing enhanced structural order and led to fine isotropic morphology0.41 cm2/Vs (hole)
Sonar et al. [148]PDPP-TBTAmbipolarThermal annealing modulated crystalline structure, charge transport0.35 cm2/Vs (hole) and 0.4 cm2/Vs (electron)
Shahid et al. [149]pDPPS3, pDPPS2TTAmbipolarThermal annealing impacted crystallinity and charge transport of the polymers1.1 cm2/Vs (hole) and 0.15 cm2/Vs (electron) from pDPPS3
Table 4. Summary of the different works reviewed in this section, including the diketopyrrolopyrrole-based semiconductors, p-type or n-type, the result findings, and mobility.
Table 4. Summary of the different works reviewed in this section, including the diketopyrrolopyrrole-based semiconductors, p-type or n-type, the result findings, and mobility.
AuthorSemiconductorTypeResult FindingsMobility
Tang et al. [107]2TzDPPA1-2DCV, 2TzDPPA2-2DCV, 2TzDPPA3-2DCVn-typeShorter alkyl side chain leads to more continuous topography and more orderly packing, favoring charge transport0.28 cm2/Vs from 2TzDPPA1-2DCV
Shin et al. [150]PDPPTT-T-10, -12, -14, -16, -18p-typeAttachment of 2-tetradecylhexadecyl side group leads to enhanced crystallinity, surface uniformity, and orderly packing1.92 cm2/Vs from PDPPTT-T-14
Chen et al. [80]PDVT-8, PDVT-10p-typePDVT-10 with a longer side chain shows enhanced topography uniformity and smaller π–π stacking distance8.2 cm2/Vs from PDVT-10
Yun et al. [81]PDPP-CNTVTAmbipolarInclusion of a nitrile group in the polymer vinyl linkage results in ambipolar behavior; charge transport depends on active layer thicknessElectron mobility of 7 cm2/Vs
Table 5. Summary of the different works reviewed in this section, including the diketopyrrolopyrrole-based semiconductors, p-type or n-type, the result findings, and mobility.
Table 5. Summary of the different works reviewed in this section, including the diketopyrrolopyrrole-based semiconductors, p-type or n-type, the result findings, and mobility.
AuthorSemiconductorTypeResult FindingsMobility
Kanimozhi et al. [151]N-CS2DPP-OD-TEGAmbipolarDevice configuration impacts ambipolar behaviors and charge transport 3 cm2/Vs (electron)
Bronstein et al. [152]Diketopyrrolopyrrole based polymerAmbipolarA much higher hole mobility was obtained than electron mobility1.95 cm2/Vs (hole)
Wang et al. [153]PDPPHD-T3AmbipolarDevice performance of PDPPHD-T3 thin-film transistor for detecting xylene0.125 cm2/Vs (hole) and 0.027 cm2/Vs (electron)
Li et al. [78]PDQTp-typeHigh-molecular-weight PDQT exhibits more superior morphology and charge transport0.97 cm2/Vs from the high-molecular-weight PDQT
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He, Z.; Asare-Yeboah, K.; Bi, S. Advances in Charge Carrier Mobility of Diketopyrrolopyrrole-Based Organic Semiconductors. Coatings 2024, 14, 1080. https://doi.org/10.3390/coatings14091080

AMA Style

He Z, Asare-Yeboah K, Bi S. Advances in Charge Carrier Mobility of Diketopyrrolopyrrole-Based Organic Semiconductors. Coatings. 2024; 14(9):1080. https://doi.org/10.3390/coatings14091080

Chicago/Turabian Style

He, Zhengran, Kyeiwaa Asare-Yeboah, and Sheng Bi. 2024. "Advances in Charge Carrier Mobility of Diketopyrrolopyrrole-Based Organic Semiconductors" Coatings 14, no. 9: 1080. https://doi.org/10.3390/coatings14091080

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