Commercialization Of Organic Solar Cells Research Articles

The Conjugated/Non-Conjugated Linked Dimer Acceptors Enable Efficient and Stable Flexible Organic Solar Cells.

The fabrication of the flexible devices with excellent photovoltaic performance and stability is critical for the commercialization of organic solar cells (OSCs). Herein, the conjugated dimer acceptor DY-TVCl and the non-conjugated dimer acceptor DY-3T based on the monomer MY-BO are synthesized to regulate the molecular glass transition temperatures (Tg) for improving the morphology stability of active layer films. And the crack onset strain values for the blend films based on dimer acceptors are superior than that of small molecule, which are beneficial for the preparation of flexible devices. Accordingly, the binary device based on PM6:DY-TVCl achieves a maximum power conversion efficiency (PCE) of 18.01%. Meanwhile, the extrapolated T80(time to reach 80% of initial PCE) lifetimes of the PM6:DY-TVCl-based device and PM6:DY-3T-based device are 3091 and 2227h under 1-sun illumination, respectively, which are better than that of the PM6:MY-BO-based device (809h). Furthermore, the flexible devices based on DY-TVCl and DY-3T exhibit the efficiencies of 15.23% and 14.34%, respectively. This work affords a valid approach to improve the stability and mechanical robustness of OSCs, as well as ensuring the reproducibility of organic semiconductors during mass production.

Efficient and Photostable Organic Solar Cells Achieved by Alloyed Dimer Acceptors with Tailored Linker Structures

AbstractHigh power conversion efficiency (PCE) and long‐term stability are prerequisites for commercialization of organic solar cells (OSCs). Herein, two dimer acceptors (DYTVT and DYTCVT) are developed with different properties through linker engineering, and study their effects as alloy‐like acceptors on the photovoltaic performance and photostability of OSCs. These ternary OSCs effectively combine the advantages of both dimer acceptors. DYTVT, characterized by its high backbone planarity, ensures elevated electron mobility and high glass‐transition temperature (Tg), leading to efficient charge transport and enhanced photostability of OSCs. Conversely, DYTCVT, with its significant dipole moment and electrostatic potential, enhances compatibility of the alloy acceptors with donors and refines the blend morphology, facilitating efficient charge generation in OSCs. Consequently, D18:DYTVT:DYTCVT OSCs exhibit higher PCE (18.4%) compared to D18:MYT (monomer acceptor, PCE = 16.5%), D18:DYTVT (PCE = 17.4%), and D18:DYTCVT (PCE = 17.0%) OSCs. Furthermore, owing to higher Tg of alloy acceptors (133 °C) than MYT (Tg = 80 °C) and DYTCVT (Tg = 120 °C), D18:DYTVT:DYTCVT OSCs have significantly higher photostability (t80% lifetime = 4250 h under 1‐sun illumination) compared to D18:MYT (t80% lifetime = 40 h) and D18:DYTCVT OSCs (t80% lifetime = 2910 h).

Design and Performance of Small-Molecule Donors with Donor-π-Acceptor Architecture Toward Vacuum-Deposited Organic Photovoltaics Having Heretofore Highest Short-Circuit Current Density.

The development of high-performance organic photovoltaic materials is of crucial importance for the commercialization of organic solar cells (OSCs). Herein, two structurally simple donor-π-conjugated linker-acceptor (D-π-A)-configured small-molecule donors with methyl-substituted triphenylamine as D unit, 1,1-dicyanomethylene-3-indanone as A unit, and thiophene or furan as π-conjugated linker, named DTICPT and DTICPF, are developed. DTICPT and DTICPF are facilely prepared via a two-step synthetic process with simple procedures. DTICPF with a furan π-conjugated linker exhibits stronger and broader optical absorption, deeper highest occupied molecular orbital (HOMO) energy levels, and better charge transport, compared to its thiophene analog DTICPT. As a result, vacuum-deposited OSCs based on DTICPF: C70 show an impressive power conversion efficiency (PCE) of 9.36% (certified 9.15%) with short-circuit current density (Jsc) up to 17.49mA cm-2 (certified 17.56mA cm-2), which is the highest Jsc reported so far for vacuum-deposited OSCs. Besides, devices based on DTICPT: C70 and DTICPF: C70 exhibit excellent long-term stability under different aging conditions. This work offers important insights into the rational design of D-π-A configured small-molecule donors for high efficient and stable vacuum-deposited OSCs.

Understanding the metal-electrode-correlated degradation of organic solar cells under illumination/thermal stress

One of the main challenges limiting the commercialization of organic solar cells (OSCs) is the instability problem. Besides the active materials, the electrode especially metal electrode correlated degradation could mainly account for the efficiency decay of a device under illumination and/or thermal stress. However, this has often been neglected compared to the active layer. An in-depth and comprehensive understanding of the electrode-correlated degradation of OSCs is essential to conquer the instability challenge of OSCs. In this work, the detailed degradation of metal electrodes under light illumination and thermal stresses is systematically studied, by probing the morphological and chemical changes. According to the in-depth analyses, a degrading mechanism is proposed for the metal-electrode-correlated degradation of OSCs, which should be taken into account for further stability investigation and the industrial production of OSCs.

Facile Synthesis of Dithienobenzothiadiazoles and D18-Cl Polymer via Na2S-Mediated Rapid Thiophene-Annulations for Organic Solar Cells.

We present a novel synthetic route for the rapid construction of dithieno[3',2':3,4;2'',3'':5,6]benzo[1,2-c][1,2,5]thiadiazoles via Na2S-promoted thiophene annulation. This method facilitated the synthesis of D18-Cl polymer, known for its efficacy as a polymer donor in bulk-heterojunction polymer solar cells. Starting from commercially available 4,7-dihalo-5,6-difluorobenzo[c][1,2,5]thiadiazole, various 4,7-dialkynylated compounds were obtained through Sonogashira reaction conditions. Subsequent Na2S-promoted thiophene annulations yielded DTBT and its derivatives in excellent yields within 10 minutes. DTBT was then utilized as a precursor for the concise synthesis of D18-Cl, benefiting from reduced synthetic steps, mild reaction conditions, decreased complexity, and high overall yields. In another route, a space group-bridged DTBT was directly constructed via Na2S-promoted thiophene annulations and converted into D18-Cl through a couple of steps. This developed protocol offers a straightforward and reliable synthetic tool, conducive to reducing complexities in the production of DTBT-based organic electronic materials, thereby advancing the potential commercialization of organic solar cells.

Aqueous Processed All-Polymer Solar Cells with High Open-Circuit Voltage Based on Low-Cost Thiophene-Quinoxaline Polymers.

Eco-friendly solution processing and the low-cost synthesis of photoactive materials are important requirements for the commercialization of organic solar cells (OSCs). Although varieties of aqueous-soluble acceptors have been developed, the availability of aqueous-processable polymer donors remains quite limited. In particular, the generally shallow highest occupied molecular orbital (HOMO) energy levels of existing polymer donors limit further increases in the power conversion efficiency (PCE). Here, we design and synthesize two water/alcohol-processable polymer donors, poly[(thiophene-2,5-diyl)-alt-(2-((13-(2,5,8,11-tetraoxadodecyl)-2,5,8,11-tetraoxatetradecan-14-yl)oxy)-6,7-difluoroquinoxaline-5,8-diyl)] (P(Qx8O-T)) and poly[(selenophene-2,5-diyl)-alt-(2-((13-(2,5,8,11-tetraoxadodecyl)-2,5,8,11-tetraoxatetradecan-14-yl)oxy)-6,7-difluoroquinoxaline-5,8-diyl)] (P(Qx8O-Se)) with oligo(ethylene glycol) (OEG) side chains, having deep HOMO energy levels (∼-5.4 eV). The synthesis of the polymers is achieved in a few synthetic and purification steps at reduced cost. The theoretical calculations uncover that the dielectric environmental variations are responsible for the observed band gap lowering in OEG-based polymers compared to their alkylated counterparts. Notably, the aqueous-processed all-polymer solar cells (aq-APSCs) based on P(Qx8O-T) and poly[(N,N'-bis(3-(2-(2-(2-methoxyethoxy)-ethoxy)ethoxy)-2-((2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-methyl)propyl)naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl)-alt-(2,5-thiophene)] (P(NDIDEG-T)) active layer exhibit a PCE of 2.27% and high open-circuit voltage (VOC) approaching 0.8 V, which are among the highest values for aq-APSCs reported to date. This study provides important clues for the design of low-cost, aqueous-processable polymer donors and the fabrication of aqueous-processable OSCs with high VOC.

Comprehensive Insight into the Structure Contribution of A2‐A1‐D‐A1‐A2 Acceptor to Performance of P3HT Solar Cells

AbstractPoly(3‐hexylthiophene) (P3HT) acting as one of the most popular and low‐cost polymers is quite suitable for commercialization of organic solar cells but suffers from low power conversion efficiency (PCE) because of the limited matching non‐fullerene acceptors (NFAs). One important reason that restricts the enhancement but remains unresolved is the undisclosed contributions of the subtle structure modification to the obvious performance change. In combination with the previous reports and this work, herein A2‐A1‐D‐A1‐A2 type NFAs with single, dual, and triple modifications based on parent BTA3 is designed, including benzyl‐substitution on A2 group (namely Bn modification), fluorine‐substitution on A1 group (namely F modification), and thieno[3,2‐b]thiophene‐substitution on D group (namely TT modification). It is finally found that the binary devices of P3HT with these NFAs underwent unexpected variations in the aspect of molecular optoelectronic property, blend morphological feature and charge generation process. The triple modification (including Bn, F, and TT) gives full play to their unique advantages and consequently increases PCE by 60%. To the knowledge, the obtained optimal PCE is one of the highest values for A2‐A1‐D‐A1‐A2 type NFAs. This study provides clearer insights into the rational substitutions on the A2‐A1‐D‐A1‐A2 acceptors matched with P3HT for high‐performance organic photovoltaics.

A–D–A'–D–A type nonfused ring electron acceptors for efficient organic solar cells via synergistic molecular packing and orientation control

AbstractNonfused ring electron acceptors (NFREAs) are promising candidates for future commercialization of organic solar cells (OSCs) due to their simple synthesis. Still, the power conversion efficiencies (PCEs) of NFREA‐based OSCs have large room for improvement. In this work, by merging end group halogenation and side chain engineering, we developed four A–D–A'–D–A type NFREAs, which we refer to as EH‐4F, C4‐4F, EH‐4Cl, and C4‐4Cl. Single crystal X‐ray diffraction revealed that multiple intermolecular S···F interactions between cyclopentadithiophene and 5,6‐difluoro‐3‐(dicyanomethylene)indanone could cause an unfavorable dimer formation, leading to ineffective π–π stackings in EH‐4F and C4‐4F, whereas no such dimer was found in EH‐4Cl and C4‐4Cl after replacing with 5,6‐dichloro‐3‐(dicyanomethylene)indanone. Moreover, although the shorter n‐butyl side chain resulted in a closer molecular packing in C4‐4Cl, EH‐4Cl (2‐ethylhexyl substitution) with proper crystallinity exhibited enhanced face‐on orientation in thin film, which is favorable for vertical charge transport and further reducing charge recombination. As a result, a PCE of 13.0% is obtained for EH‐4Cl‐based OSC with a fill factor of 0.70. This work highlights the importance of molecular packing and orientation control toward future high‐performance A–D–A'–D–A type NFREAs.

Enhanced crystal network and charge transfer of non-fused ring electron acceptors via interchain interaction for efficient and stable organic solar cells

This research provides valuable references for the design of electron acceptors addressing the “efficiency-cost-stability” triangle, thus advancing the commercialization of organic solar cells (OSCs).

Efficient organic solar cells based on low-cost pentacyclic fused-ring small molecule acceptors with a fill factor over 80%

Small molecule acceptor (SMA) materials with pentacyclic fused-ring backbone are considered as promising candidates for balancing the low-cost and high photovoltaic performance for commercialization of organic solar cells (OSCs). However,...

Multi-functionally ferroelectric polymer promotes highly-efficient large-area organic solar cells with excellent comprehensive performance

Developing high-performance active layer with excellent comprehensive performance is very crucial for the commercialization of organic solar cells (OSCs). Here, we demonstrate the multi-function of ferroelectric polymer polyvinylidene fluoride (PVDF) in improving the device comprehensive performance including device efficiency, stability, green-solvent large-area printing and mechanical property. Addition of PVDF not only enhances the build-in field to promote charge kinetics, but also develops robust network through strong interaction and chain entanglement between polymer donor and PVDF. Importantly, such robust network effectively protects the active layer from excessive flushing/swelling between D/A component to optimize layer-by-layer (LBL) deposition, induce a favorable vertical phase distribution and prolong the film-forming process, consequently facilitating green-solvent blade-coating printing, improving device efficiency and stability, and enhancing device mechanical flexibility. Due to the multiple advantages of PVDF, the PM6/BTP-eC9 obtains an excellent efficiency of 18.35% for BTP-eC9-based LBL devices. By blade-coating printing with green solvent, one of the highest efficiencies of 16.40% is achieved for large-area (1.21 cm2) binary device. Particularly, toughness is used to comprehensively evaluate mechanical property of OSCs, showing significant improvement with simultaneously enhanced fracture strength and tensile strain, and enabling small molecule-based system even have comparable mechanical flexibility and comprehensive performance to the all-polymer system.

Regiospecific Incorporation of Acetylene Linker in High‐Electron Mobility Dimerized Acceptors for Organic Solar Cells with High Efficiency (18.8%) and Long 1‐Sun Lifetime (> 5000 h)

AbstractThe commercialization of organic solar cells (OSCs) requires both high power conversion efficiency (PCE) and long‐term stability. However, the lifetime of the OSCs containing small‐molecule acceptors (SMA) should be significantly enhanced. In this study, a series of planarity‐controlled is developed, high electron mobility dimerized SMAs (DSMAs) and realize OSCs with high‐performance (PCE = 18.8%) and high‐stability (t80% lifetime = 5380 h under 1‐Sun illumination). An acetylene linker with a planar triple bond is designed for dimerization of SMA units to afford the high backbone planarity necessary to achieve high crystallinity and electron mobility. To further engineer the molecular conformation and electron mobility of the DSMAs, different regioisomers of a Y‐based SMA are dimerized to yield three regioisomerically distinct DSMAs, denoted as DYA‐I, DYA‐IO, and DYA‐O, respectively. It is found that the crystallinity, electron mobility, and glass transition temperature of the DSMAs gradually increase in the order of DYA‐O, DYA‐IO, and DYA‐I, which, in turn, enhance the PCE and device stability of the resulting OSCs; DYA‐O (PCE = 16.45% and t80% lifetime = 3337 h) < DYA‐IO (PCE = 17.54% and t80% lifetime = 4255 h) < DYA‐I (PCE = 18.83% and t80% lifetime = 5380 h).

Asymmetric Polymer Additive for Morphological Regulation and Thermally Stable Organic Solar Cells.

High thermal stability is crucial for the commercialization of organic solar cells (OSCs). The thermal stability of OSCs has been improved using the tailoring blend morphology of bulk heterojunctions (BHJs). Herein, we demonstrated thermally stable OSCs in a ternary blended system containing low-crystalline semiconducting polymers (asy-PNDI1FTVT and PTB7-Th) and a non-fullerene acceptor (Y6). The asymmetric n-type semiconducting polymer (asy-PNDI1FTVT) differed from general symmetric semiconducting polymers as it randomly substituted fluorine atoms at the donor moiety (TVT), resulting in significantly lower crystallinity. asy-PNDI1FTVT in PTB7-Th:Y6 exhibited a well-mixed morphology at the BHJ and efficiently facilitated the charge dissociation process with an enhanced fill factor and power conversion efficiency. Furthermore, the ternary system of PTB7-Th:Y6:asy-PNDI1FTVT suppressed phase separation with negligible burn-in loss and performance degradation under thermal stress. The experiments showed that our devices without encapsulation retained over 90% of their initial efficiencies after 100 h at 65 °C. These results show significant potential for the development of thermally stable OSCs with reasonable efficiency.

A Non‐Halogenated Polymer Donor Based on Imide Unit for Organic Solar Cells with Efficiency Nearly 16%

Comprehensive SummaryNon‐halogenated polymers have great potential in the commercialization of organic solar cells (OSCs) due to their advantages in the manufacturing process. However, high‐performance donor polymers are limited to a small amount of building blocks. Herein, we utilize as building block 4H‐dithieno[3,2‐e:2',3'‐g]isoindole‐4,6(5H)‐dione (DTID) to design and synthesize a relevant non‐halogenated polymer PBTID for active layers in OSCs. PBTID exhibits a strong absorption in the wavelength range of 400—600 nm with a distinctly wide optical bandgap of 2.06 eV, a low‐lying highest occupied molecular orbital (HOMO) energy level of −5.53 eV. In addition, this polymer has a very strong aggregation effect in solution and could form nanoscale fibrils in the neat film. Consequently, when blended with the non‐fullerene acceptor Y6, the devices achieve a prominent PCE of 15.8% with a high Voc of 0.87 V. The Voc and PCE values are one of the highest values in the non‐halogenated polymer donor‐based OSCs reported to date.

Carbon-Based Electrodes for Organic Solar Cells.

Organic solar cells (OSCs) are a promising low-cost thin-film photovoltaic technology while the fabrication of transparent conductive oxide (TCO) and metal electrodes still remains a factor that hinders the scaling-up and commercialization of OSCs. Carbon-based materials are regarded as potential alternatives due to their excellent properties, such as low cost, solution processibility, high conductance, and good chemical stability. In this mini-review, the recent progress of carbon-based materials such as graphite, carbon nanosheets, graphene, and carbon nanotubes to replace the TCO and metal electrodes of OSCs is surveyed. The preparation methods of different carbon-based materials are also discussed. Based on current progress, we summarize the outlooks and challenges of carbon-based electrodes. We anticipate this mini-review will inspire more research efforts to develop high-performance and OSC-matched carbon materials for more efficient and stable carbon-electrode-based OSCs.

Efficient Large Area All‐Small‐Molecule Organic Solar Cells Fabricated by Slot‐Die Coating with Nonhalogen Solvent

AbstractThe commercialization of organic solar cells (OSCs) requires the use of roll‐to‐roll coating technology. However, it is generally believed that all‐small‐molecule (ASM) systems cannot form high‐quality films in most film‐fabrication technologies except for spin coating, mainly due to their strong crystallinity and low solution viscosity. Herein, it is found that the small molecule donor and acceptor system with strong intermolecular interaction can weaken the molecular self‐aggregation during film formation. As a result, all‐small‐molecule organic solar cells (ASM‐OSCs) are successfully fabricated using the green solvent tetrahydrofuran via spin coating as well as slot‐die coating technology. Under the optimal conditions, the devices achieve power conversion efficiency (PCE) of 14.05% and 13.41% prepared by spin coating and slot‐die coating, respectively. Moreover, a large‐area device with an area of 1 cm2 achieve a PCE of 10.65% by slot‐die coating. The study of the device performance and the active layer morphology reveal a unique film optimization mechanism in ASM‐OSCs. In the slot‐die coating process, a high‐quality film is formed due to the significantly suppressed crystallinity of the small molecule donor; with further thermal annealing, the crystallization‐induced phase separation enables an optimized morphology. This study proves that high‐performance ASM‐OSCs can be fabricated by the industrial‐compatible method.

Efficient Fully‐Sprayed Organic Solar Cells with Coffee‐Ring‐Free Photoactive Layer and Alloy Top‐Electrode

AbstractDepositing all functional layers (including the top electrode) with spray methods is highly desirable and challenging for the eventual commercialization of organic solar cells (OSCs). This work addresses two key challenges toward fully‐sprayed OSCs: i) the printing of a high‐quality photoactive layer free of coffee rings and ii) the spray of the top electrode without the need of evaporation nor solvents. To eliminate coffee rings caused by individual droplets, the photoactive layer is deposited by electrospray on the cooled substrate. The reduced temperature slows down the solvent evaporation, promotes merging of individual droplets, and suppresses the formation of coffee rings. By optimizing the drying temperature, homogeneous films without coffee rings are obtained. The improved active‐layer morphology facilitates charge transport and reduces recombination. The device prepared by the coldplate‐assisted electrospray reaches a power conversion efficiency (PCE) of 17.13%. In addition, an alloy with the melting point of 62 °C is spray‐printed as the top electrode using an airbrush. The spray process is optimized by the trade‐off between the coverage rate and the film thickness. OSCs with the alloy electrode achieve the highest PCE of 16.26%. The fully‐sprayed OSCs exhibit PCEs up to 15.09%, demonstrating a viable route toward fully‐sprayed OSCs with high‐performance.

Linker Engineering of Dimerized Small Molecule Acceptors for Highly Efficient and Stable Organic Solar Cells

High power conversion efficiency (PCE) and long-term stability are important requirements for commercialization of organic solar cells (OSCs). In this study, we demonstrate efficient (PCE = 18.60%) and stable (t80% lifetime > 4000 h) OSCs by developing a series of dimerized small-molecule acceptors (DSMAs). We prepared three different DSMAs (DYT, DYV, and DYTVT) by using different linkers (i.e., thiophene, vinylene, and thiophene– vinylene– thiophene), to connect their two Y-based building blocks. We find that the crystalline properties and glass transition temperature (Tg) of DSMAs can be systematically modulated by the linker selection. A DYV-based OSC achieves the highest PCE (18.60%) among the DSMA-based OSCs owing to the appropriate backbone rigidity of DYV, leading to an optimal blend morphology and high electron mobility. Importantly, the DYV-based OSC also demonstrates excellent operational stability under 1-sun illumination, i.e., a t80% lifetime of 4005 h.

A robust and thickness-insensitive hybrid cathode interlayer for high-efficiency and stable inverted organic solar cells

A robust and thickness-insensitive cathode interlayer (PFOPy-N) consisting of a cross-linkable interfacial polymer (PFOPy) and n-type self-doped interfacial molecule (PDINN) is developed for high-efficiency and stable inverted organic solar cells.

A Mini Review on the Development of Conjugated Polymers: Steps towards the Commercialization of Organic Solar Cells

This review article covers the synthesis and design of conjugated polymers for carefully adjusting energy levels and energy band gap (EBG) to achieve the desired photovoltaic performance. The formation of bonds and the delocalization of electrons over conjugated chains are both explained by the molecular orbital theory (MOT). The intrinsic characteristics that classify conjugated polymers as semiconducting materials come from the EBG of organic molecules. A quinoid mesomeric structure (D-A ↔ D+ = A-) forms across the major backbones of the polymer as a result of alternating donor-acceptor segments contributing to the pull-push driving force between neighboring units, resulting in a smaller optical EBG. Furthermore, one of the most crucial factors in achieving excellent performance of the polymer is improving the morphology of the active layer. In order to improve exciton diffusion, dissociation, and charge transport, the nanoscale morphology ensures nanometer phase separation between donor and acceptor components in the active layer. It was demonstrated that because of the exciton's short lifetime, only small diffusion distances (10-20 nm) are needed for all photo-generated excitons to reach the interfacial region where they can separate into free charge carriers. There is a comprehensive explanation of the architecture of organic solar cells using single layer, bilayer, and bulk heterojunction (BHJ) devices. The short circuit current density (Jsc), open circuit voltage (Voc), and fill factor (FF) all have a significant impact on the performance of organic solar cells (OSCs). Since the BHJ concept was first proposed, significant advancement and quick configuration development of these devices have been accomplished. Due to their ability to combine great optical and electronic properties with strong thermal and chemical stability, conjugated polymers are unique semiconducting materials that are used in a wide range of applications. According to the fundamental operating theories of OSCs, unlike inorganic semiconductors such as silicon solar cells, organic photovoltaic devices are unable to produce free carrier charges (holes and electrons). To overcome the Coulombic attraction and separate the excitons into free charges in the interfacial region, organic semiconductors require an additional thermodynamic driving force. From the molecular engineering of conjugated polymers, it was discovered that the most crucial obstacles to achieving the most desirable properties are the design and synthesis of conjugated polymers toward optimal p-type materials. Along with plastic solar cells (PSCs), these materials have extended to a number of different applications such as light-emitting diodes (LEDs) and field-effect transistors (FETs). Additionally, the topics of fluorene and carbazole as donor units in conjugated polymers are covered. The Stille, Suzuki, and Sonogashira coupling reactions widely used to synthesize alternating D-A copolymers are also presented. Moreover, conjugated polymers based on anthracene that can be used in solar cells are covered.