A Volatile Solid Additive Enables Oligothiophene All-Small-Molecule Organic Solar Cells with Excellent Commercial Viability

The commercial viability of all-small-molecule (ASM) organic solar cells (OSCs) requires high efficiency, long-term stability, and low-cost production. However, satisfying all these factors at the same time remains highly challenging. Herein, a volatile solid additive, namely, 1,8-dichloronaphthalene (DCN) is demonstrated to simultaneously enhance the power conversion efficiency (PCE) and the storage, thermal as well as photo stabilities of oligothiophene ASM-OSCs with concise and low-cost syntheses. The improved PCEs are mainly due to the DCN-induced morphology control with improved exciton dissociation and reduced non-geminate recombination. Notably, the PCE of 16.0% stands as the best value for oligothiophene ASM-OSCs and is among the top values for all types of binary ASM-OSCs. In addition, devices incorporating DCN have shown remarkable long-term stability, retaining over 90% of their initial PCE after dark storage aging of 3000 h and thermal or light stressing of 500 h. The findings demonstrate that the volatile-solid-additive strategy can be a simple yet effective method of delivering highly efficient and stable oligothiophene ASM-OSCs with excellent commercial viability.     

Quadrupole Moment Induced Morphology Control Via a Highly Volatile Small Molecule in Efficient Organic Solar Cells

Developing novel solid additives has been regarded as a promising strategy to achieve highly efficient organic solar cells with good stability and reproducibility. Herein, a small molecule, 2,2′-(perfluoro-1,4-phenylene)dithiophene (DTBF), designed with high volatility and a strong quadrupole moment, is applied as a solid additive to implement active layer morphology control in organic solar cells. Systematic theory simulations have revealed the charge distribution of DTBF and its analog and their non-covalent interaction with the active layer materials. Benefitting from the more vital charge–quadrupole interaction, the introduction, and volatilization of DTBF effectively induced more regular and condensed molecular packing in the active layer, leading to enhanced photoelectric properties. Thus, high efficiency of over 17% is obtained in the DTBF-processed devices, which is higher than that of the control devices. Further application of DTBF in different active layer systems contributed to a deeper comprehension of this type of additive. This study highlights a facile approach to optimizing the active layer morphology by finely manipulating the quadrupole moment of volatile solid additives.     

Solid Solvation Assisted Electrical Doping Conserves High-Performance in 500 nm Active Layer Organic Solar Cells

Organic solar cells (OSCs) process fascinating solution-printing capability to achieve low-cost and large-scale manufacture. However, the rapid power conversion efficiency (PCE) decay with active layer thickness enlargement inhibits the implement of OSCs’ potential advantages. To overcome the bottlenecks of PCE decay in thick active layer OSCs, the electrical doping with componential selectivity in bulk heterojunction (BHJ) film is achieved by introducing a solid solvation additive. Benefiting from the higher exciton splitting efficiency together with the longer drift (L_dr) and diffusion (L_diff) lengths, an OSC with 100 nm BHJ film demonstrates a PCE increment from 16.44% to 18.24% with prolonged dark and illuminated storage stabilities. Applying the solid solvation assisted (SSA) doping method in the OSCs with 500 nm active layer, the PCE significantly increases by 31.9%, from the original value of 11.79% to 15.55%. It further improves to 15.84% in a ternary blend thick-film device, which is the record value to the best of our knowledge. Besides, the SSA doping narrows the PCE gap between the 0.04 and 1 cm² devices. All improvements demonstrate the great potential of SSA doping for OSC commercial manufacture, since it optimizes the photovoltaic performance under all practical conditions of long-term, thick-film, and large-area.     

Controlling Kinetic Quenching Depth Toward High-Performance and Photo-Stable Organic Solar Cells Printed from a Non-Halogenated Solvent

The investigation of drying dynamics and kinetic quenching depth related degradation of high-performance photoactive materials with scalable coating techniques demands significant research attention. Herein, film formation kinetics regulated crystallinity, preferential orientation and vertical phase separation of the active layers is revealed, which then further affects exciton diffusion, dissociation, charge-transport and recombination processes. By suppressing over aggregation/crystallization in slow drying process and overcoming quenching of disordered liquid phase in fast-dried films, the optimized PM6:BTP-eC9-based organic solar cells  obtain power conversion efficiencies  up to 16.81%. In addition, photoluminescence lifetime distribution is found to be an alternative probe for kinetic quenching depth that governs the degradation rate. This study provides valuable insights into the control of thin film formation kinetics during scalable processing and develops an effective way to associate the kinetic quenching depth with morphological degradation for mechanistic understanding of long-term stability.     

Rational Mutual Interactions in Ternary Systems Enable High-Performance Organic Solar Cells

Ternary organic solar cells (TOSCs) offer a facile and efficient approach to increase the power conversion efficiencies (PCEs). However, the critical roles that guest components play in complicated ternary systems remain poorly understood. Herein, two acceptors named LA1 and LA9 with differing crystallinity are investigated. The overly crystalline LA9 induces large self-aggregates in PM6:LA9 binary system, resulting in a lower PCE (13.12%) compared to PM6:LA1 device (13.89%). Encouragingly, both acceptors are verified as efficient guest candidates into the host binary PM6:NCBDT-4Cl (PCE = 13.48%) and afford markedly improved PCEs up to 15.39% and 15.75% in LA1 and LA9 ternary devices, respectively. Interestingly, the higher crystallinity LA9 reveals smaller interaction energies with both the host acceptor and donor PM6. Compared to LA1, the appropriate mutual interactions in the LA9 ternary system not only induces the orderly crystallinity of PM6 but also better compatibility with the host acceptor, generating further optimized molecular orientations and ternary morphology. Therefore, enhanced charge transport and minimized recombination loss are detected in LA9 ternary devices, affording the most competitive performance among Y6-sbsent TOSCs. This work suggests that complicated intermolecular interactions should be seriously considered when fabricating state-of-the-art multiple components OSCs.     

Diffusion-Limited Accepter Alloy Enables Highly Efficient and Stable Organic Solar Cells

Organic solar cells (OSCs) are designed based on a blend of polymer donor and small molecular acceptor whereby the thermodynamic relaxation of the morphology raises the concerns related to operational stability. Herein, it is demonstrated that the classical Y6-based binary device can be stabilized by using its derivative of ZCCF3 as the third component, which is designed with the replacing of the thiadiazole group on Y6 with the trifluoromethyl substituted diazepine unit. ZCCF3 delivers not only higher glass transition temperature (T_g) than Y6 but also have hyper-miscibility with Y6, contributing to a favorable diffusion-limited Y6:ZCCF3 alloy when blended with polymer donor. Consequently, a champion power conversion efficiency of 18.54% is achieved in the optimal PM6: Y6: ZCCF3 devices, which can retain their 80% initial efficiency of up to 360 h. This study highlights the importance of high T_g of the third component and its derived hyper-miscible accepter alloys in achieving highly efficient and stable OSCs.     

Volatile Solid-Assisted Molecular Assembly Enables Eco-Friendly Processed Organic Photovoltaic Cells with High Efficiency and Photostability

Achieving environmentally friendly solvent-processed high-performance organic photovoltaic cells (OPVs) is a crucial step toward their commercialization. Currently, OPVs with competitive efficiencies rely heavily on harmful halogenated solvent additives. Herein, the green and low-cost 9-fluorenone (9-FL) is employed as a solid additive. By using the o-xylene/9-FL solvent system, the PM6:BTP-eC9-based devices deliver power-conversion efficiencies of 18.6% and 17.9% via spin-coating and blade-coating respectively, outperforming all PM6:Y-series binary devices with green solvents. It is found that the addition of 9-FL can regulate the molecular assembly of both PM6 and BTP-eC9 in film-formation (molecule-level mixing) and post-annealing (thermal-assisted molecular reorganization with additive volatilization) stages, so as to optimize the blend morphology. As a result, the charge transport ability of donor and acceptor phases are simultaneously enhanced, and the trap-assisted recombination is reduced, which contributes to the higher short-circuit current density and fill factor. Moreover, the generation of photo-induced traps is significantly suppressed, resulting in improved stability under illumination. It is further demonstrated the excellent universality of 9-FL in various photoactive systems, making it a promising strategy to advance the development of eco-friendly OPVs.     

Developing Efficient Benzene Additives for 19.43% Efficiency of Organic Solar Cells by Crossbreeding Effect of Fluorination and Bromination

Employing volatile solid additives have emerged as a promising method to optimize the morphology and improve the performance of organic solar cells (OSCs). However, principles governing the efficient design of solid additives remain elusive. Herein, the programmed fluorination and/or bromination on benzene core to develop efficient additives for OSCs is reported. The programmed fluorination and/or bromination endow the five halogen benzene derivatives, 1,3,5-trifluorobenzene, hexafluorobenzene, 1,3,5-tribromo-2,4,6-trifluorobenzene (TFTB), 1,3,5-tribromobenzene, and hexabromobenzene, with different melting and boiling points, volatility, as well as interactions with the host blend. Studies indicate that the additives with extremely high and low volatility are almost powerless and even detrimental to the morphology evolution. Among them, the combination of fluorine and bromine atoms on TFTB not only enables the more appropriate m.p./b.p. and volatility, but also exerts stronger molecular interactions with the host blend, giving rise to higher ordered molecular packing and more favorable morphology. Importantly, TFTB exhibits good universality to optimize the performances of OSCs with high power conversion efficiencies (PCEs; over 18%) in a group of binary blend systems, and an impressive PCE of 19.43% in the ternary PBTz-F:PM6:L8-BO system.     

Anthracene-Assisted Morphology Optimization in Photoactive Layer for High-Efficiency Polymer Solar Cells

Currently, morphology optimization methods for the fused-ring nonfullerene acceptor-based polymer solar cells (PSCs) empirically follow the treatments originally developed in fullerene-based systems, being unable to meet the diverse molecular structures and strong crystallinity of the nonfullerene acceptors. Herein, a new and universal morphology controlling method is developed by applying volatilizable anthracene as solid additive. The strong crystallinity of anthracene offers the possibility to restrict the over aggregation of fused-ring nonfullerene acceptor in the process of film formation. During the kinetic process of anthracene removal in the blend under thermal annealing, donor can imbed into the remaining space of anthracene in the acceptor matrix to form well-developed nanoscale phase separation with bi-continuous interpenetrating networks. Consequently, the treatment of anthracene additive enables the power conversion efficiency (PCE) of PM6:Y6-based devices to 17.02%, which is a significant improvement with regard to the PCE of 15.60% for the reference device using conventional treatments. Moreover, this morphology controlling method exhibits general application in various active layer systems to achieve better photovoltaic performance. Particularly, a remarkable PCE of 17.51% is achieved in the ternary PTQ10:Y6:PC₇₁BM-based PSCs processed by anthracene additive. The morphology optimization strategy established in this work can offer unprecedented opportunities to build state-of-the-art PSCs.     

Efficient Quaternary Organic Solar Cells with Parallel‐Alloy Morphology

Two compatible donors (PBDB‐T and PTB7‐Th) and two miscible acceptors (ITIC and FOIC) are employed to deliver a parallel‐alloy morphology model in non‐fullerene‐based quaternary organic solar cells. PBDB‐T and PTB7‐Th form a parallel link with a slight adjustment of molecular packing into enhanced face‐on crystallites while ITIC disperses into discontinuous FOIC microcrystal regions to form continuous and ordered alloy‐like acceptor phases. Characterization of blend morphology highlights the parallel‐alloy model—enabled by the introduction of PBDB‐T and ITIC, which contributes to improved molecular packing and reduced domain size resulting in efficient charge generation and consistent transport channels. This successful parallel‐alloy quaternary blend morphology demonstrates an enhanced optical absorption, optimized domain size, and nanostructures toward simultaneous improvement in charge transfer and transport. Therefore, a power conversion efficiency of 12.52% is realized for a quaternary device which is 6% higher than the ternary device (PBDB‐T:PTB7‐Th:FOIC) and 12% higher than the binary device (PTB7‐Th:FOIC). Domination of quaternary devices over ternary and binary blends, which is another feasible way to realize highly efficient devices through further investigation of quaternary OSCs, is presented.     

Natural Bio-additive Chlorophyll Derivative Enables 17.30% Efficiency Organic Solar Cells

Additive-assisted donor and acceptor domain regulation is regarded as an effective strategy to further release the potential photovoltaic performance of the existing organic solar cells (OSCs). Meanwhile, it is also critical to find high-efficient, stable, non-toxic, and low-cost biological materials as bio-additives to replace the traditional toxic halogen-based additives. In this study, bio-additives derived from a natural chlorophyll pigment named as ZnChl and H₂Chl are employed to optimize the morphology and molecular stack of the PM6:Y6 active layer. The eutectic molecular stack of the blends is more ordered and tighter after introducing the bio-additive chlorophyll derivatives to the system compared to the pristine PM6:Y6 blends. Owing to such a fine-tuned donor-acceptor microstructure network, the photovoltaic performance of the H₂Chl bio-additive-based OSC achieves a 17.30% PCE and ZnChl-based device obtains an efficiency of 16.61%, which is much higher than that of the control device with a 15.97% PCE. The result proves the feasibility of introducing environmental- and eco-friendly chlorophyll derivatives as bio-additives to further improve the photovoltaic performance of the OSCs.     

Achieving Organic Solar Cells with an Efficiency of 18.80% by Reducing Nonradiative Energy Loss and Tuning Active Layer Morphology

The efficiency of organic solar cells (OSCs) is primarily limited by their significant nonradiative energy loss and unfavorable active layer morphology. Achieving high-efficiency OSCs by suppressing nonradiative energy loss and tuning the active layer morphology remains a challenging task. In this study, an acceptor named CH-ThCl is designed, featuring an extended conjugation central core, dichlorodithienoquinoxaline. The incorporation of chlorine-substituted extended conjugation in the central core enhances the acceptor's rigidity and promotes J-aggregation, leading to improved molecular luminescent efficiency and a reduction in nonradiative energy loss. A binary device based on PM6: CH-ThCl demonstrates a power conversion efficiency (PCE) of 18.16% and exhibits a high open-circuit voltage (V_oc) of 0.934 V, attributed to the remarkably low nonradiative energy loss of 0.21 eV. Furthermore, a ternary device is fabricated by incorporating CH-6F as the third component, resulting in a significantly enhanced PCE of 18.80%. The ternary device exhibits improvements in short-circuit current (J_sc) and fill factor (FF) while maintaining the V_oc, primarily due to the optimized active layer morphology. These results highlight the effectiveness of combining the reduction of nonradiative energy loss and precise tuning of the active layer morphology as a viable strategy for achieving high-efficiency OSCs.     

High-Performance Green Thick-Film Ternary Organic Solar Cells Enabled by Crystallinity Regulation

The power conversion efficiency (PCE) of organic solar cells (OSCs) has reached high values of over 19%. However, most of the high-efficiency OSCs are fabricated by spin-coating with toxic solvents and the optimal photoactive layer thickness is limited to 100 nm, limiting practical development of OSCs. It is a great challenge to obtain ideal morphology for high-efficiency thick-film OSCs when using non-halogenated solvents due to the unfavorable film formation kinetics. Herein, high-efficiency ternary thick-film (300 nm) OSCs with PCE of 15.4% based on PM6:BTR-Cl:CH1007 are fabricated by hot slot-die coating using non-halogenated solvent (o-xylene) in the air. Compared to PM6:BTR-Cl:Y6 blends, the stronger pre-aggregation of CH1007 in solution induces the earlier aggregation of CH1007 molecules and longer aggregation time, and thus results in high and balanced crystallinity of donors and acceptor in CH1007-based ternary film, which led to high-carrier mobility and suppressed charge recombination. The ternary strategy is further used to fabricate high-efficiency, thick-film, large-area, and flexible devices processed from non-halogenated solvents, paving the way for industrial development of OSCs.     

Elimination of Drying-Dependent Component Deviation Using a Composite Solvent Strategy Enables High-Performance Inkjet-Printed Organic Solar Cells with Efficiency Approaching 16%

Inkjet printing (IJP) is a roll-to-roll (R2R) compatible fabrication method for large-area organic solar cells (OSCs). Unlike the coating process, the films are formed through droplet leveling and merging during IJP, and the pre-deposited droplets are partly dissolved by the subsequent droplets. Such a process yields undesired printing pattern lines, especially in large-area printed films. This study reveals that such a temperature-dependent “drying lines-related” phase separation morphology has caused component variation in the organic blend films, which leads to an obvious inhomogeneity of photocurrent in the printed OSCs. Such a phenomenon is attributed to the solubility difference between organic donor and acceptor molecules in the main printing solvent. A composite solvent strategy of ortho-dichlorobenzene (oDCB)/trimethylbenzene (TMB) and tetralin (THN) is developed to solve this problem. The introduction of THN suppresses the formation of printing drying lines during high-temperature printing due to the preferential miscibility of acceptor in THN, leading to the efficiency improvement to 13.96% and 15.78% for the binary and ternary devices. In addition, the 1 cm² device with a disruptive pattern gives an efficiency of 12.80% and a certificated efficiency of 12.18%.     

High-Efficiency (16.93%) Pseudo-Planar Heterojunction Organic Solar Cells Enabled by Binary Additives Strategy

Acquiring precision adjustable morphology of the blend films to improve the efficiency of charge separation and collection is a constant goal of organic solar cells (OSCs). Here, the above problem is improved by synergistically combining the sequential deposition (SD) method and the additive general strategy. By adding one additive 1,10-decanediol (DDO) into PM6 and another 1-chloronaphthalene (CN) into Y6, the molecule orientation of PM6 and the crystallite texture of the Y6 all become order. During the SD processing, a vertical phase separation OSCs device is formed where the donor enrichment at the anode and acceptor enrichment at the cathode. In comparison, the SD OSCs device with only CN additive still displays the bulk-heterojunction morphology similar to PM6:Y6 blend film. The morphology with vertical phase distribution can not only inhibit charge recombination but also facilitate charge collection, finally enhancing the fill factor (FF) and photocurrent in binary additives SD-type OSCs. As a result, the binary additives SD-type OSCs with blend film PM6 + DDO/Y6 + CN exhibit a high FF of 77.45%, enabling a power conversion efficiency as high as 16.93%. This work reveals a simple but effective approach for boosting high-efficiency OSCs with ideal morphologies and demonstrates that the additive is a promising processing alternative.     

Asymmetric Alloy Acceptor Strategy Guided by Similarity Principle Enables Highly Efficient and Stable Organic Solar Cells

Introducing the guest materials into binary active layer to construct ternary organic solar cells (OSCs) is widely used to improve device performance. Nevertheless, designing the guest materials is a challenging task. Herein, asymmetric alloy acceptor strategy guided by similarity principle to design the guest materials is employed. Two small molecular acceptors (ZH1 with symmetric end groups and ZH2 with asymmetric end groups) with the same skeleton to the host acceptor are synthesized and compared. Compared to symmetric ZH1, asymmetric ZH2 delivers a remarkably higher efficiency (3.86% vs 13.03%) when paired with PM6, benefiting from the larger dipole moment to facilitate charge dynamics and more favorable morphology. More importantly, by introducing ZH1 and ZH2 as the guest materials into the PM6:BTP-eC9 blend, both ZH1 and ZH2 well alloy with acceptor BTP-eC9 due to the similar skeleton, not only providing a complementary absorption, but also optimizing and stabilizing the blend morphology. Notably, the asymmetric alloy acceptor distinctly outperforms symmetric alloy acceptor, PM6:BTP-eC9:ZH2-based device achieves an outstanding efficiency of 18.75% with better stability and reduced non-radiative energy loss. Therefore, developing asymmetric alloy acceptor is an effective strategy to develop high-performance and stable OSCs.     

CuPc-PCTDA有机薄膜太阳电池性能模拟与结构优化

针对CuPc-PTCDA有机小分子太阳电池,根据光学干涉效应和扩散理论,建立了非相干光吸收模型和激子传输模型,利用Matlab软件模拟了限制有机光伏效率的光吸收和激子扩散过程,模拟了不同激子扩散长度下CuPc层内激子浓度分布,由此得到了光电流密度和外量子效率与CuPc层膜厚的关系;模拟得到了外量子效率与PTCDA、CuPc各层膜厚的关系,进而优化有机层的结构,以此达到了提高器件光伏效率的目的。     

Spatially Orthogonal 2D Sidechains Optimize Morphology in All-Small-Molecule Organic Solar Cells

Organic semiconductors consist of a conjugated backbone and flexible sidechains. Compared to the meticulous design of backbones, less attention has been paid to the investigation of sidechains, in particular their spatial orientation. Herein, three non-fullerene acceptors, anti-PDFC, syn-PDFC, and PDFC-Ph, are applied in all-small-molecule organic solar cells (ASM-OSCs) to reveal the varied effects of sidechains on morphology and device performance. With spatially orthogonal alkyl chains, anti-PDFC and syn-PDFC show unique bimodal lamellar packing and moderate crystallinity. When blending with an efficient binary BTR-Cl/Y6 system, anti-PDFC as well as syn-PDFC not only form their own crystal phase but also improve the packing order of BTR-Cl, consequently enhancing the power conversion efficiency (PCE) of ternary ASM-OSC to be 14.56%. However, although PDFC-Ph has an identical backbone with anti-PDFC, the alternated sidechains make it relatively amorphous, which is prone to damage the original packing of the host donor/acceptor, and thus deteriorating the device performance. When PC₇₁BM is added to optimize the morphology further, the triple-acceptor device involving anti-PDFC realizes a PCE of 15.67%, which is among the best efficiencies in ASM-OSCs. This study demonstrates that a multi-dimensional sidechain can optimize the morphology of a bulk heterojunction as effective as a conjugated backbone.     

Simple and Low-Cost Vanadyl Oxalate as Hole Transporting Layer Enables Efficient Organic Solar Cells

Organic solar cells (OSCs) with the conventional configuration usually use polyethylenedioxythiophene:polystyrene sulfonate (PEDOT:PSS) as the hole-transporting layer (HTL); however, its acidity tends to affect the performance and long-term stability of the devices. Therefore, replacing PEDOT:PSS with other more stable HTLs is essential for realizing the practical applications of OSCs. To achieve this goal, a simple and low-cost vanadyl oxalate (VOC₂O₄) is identified as a HTL to facilitate high power conversion efficiencies (PCEs), good stability, and high thickness tolerance to be achieved in OSCs. The VOC₂O₄ thin film can be easily prepared by spin-coating from its aqueous solution onto ITO/glass substrate and thermally annealed at 100 °C to exhibit high transmittance, conductivity, and work function. It can be applied as a robust HTL with wide processing conditions, especially after being heated at 200 °C and treated with UV-ozone (UVO) to afford a very high PCE of 18.94% in OSCs. This value is among the highest PCEs obtained for binary OSCs. In addition, the derived OSCs exhibit high thickness tolerance and better stability than those based on PEDOT:PSS as HTL. These results reveal that VOC₂O₄ is an excellent HTL for OSCs, having great potential for large-area device applications.     

Impact of Blend Morphology on Interface State Recombination in Bulk Heterojunction Organic Solar Cells

This work is a reinvestigation of the impact of blend morphology and thermal annealing on the electrical performance of regioregular‐P3HT:PC₆₀BM bulk heterojunction organic solar cells. The morphological, structural, and electrical properties of the blend are experimentally investigated with atomic force microscopy, X‐ray diffraction, and time‐of‐flight measurements. Current–voltage characteristics of photodiode devices are measured in the dark and under illumination. Finally, the existence of exponential electronic band tails due to gap states is experimentally confirmed by measuring the device spectral response in the subband gap regime. This method reveals the existence of a large density of gap states, which is partially and systematically reduced by thermal annealing. When the band tails are properly accounted for in the drift and diffusion simulations, experimentally measured charge transport characteristics, under both dark and illuminated conditions and as a function of annealing time, can be satisfactorily reproduced. This work further confirms the critical impact of tails states on the performance of solar cells.