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Achieving an ideal morphology to realize efficient charge generation and transport is an imperative avenue to improve the photovoltaic performance of all small‐molecule organic solar cells (SM‐OSCs). Here, ternary SM‐OSCs are fabricated based on a new small molecule donor, SM‐mB, and an alloyed blend acceptor of Y6 and its derivative, L8‐BO, and desirable hierarchical morphology with appropriate nanoscale phase separation is successfully realized through adjusting the thermal annealing treatment conditions and compositions of mixed acceptors in the active layer. Then the ternary SM‐OSCs achieve an excellent PCE of 17.06 %, which is one of the best results for the SM‐OSCs so far. The desirable morphology can be ascribed to the optimization of the miscibility‐driven donor and acceptor blend morphology that takes full advantage of the individual advantages of both acceptors, which facilitate efficient charge generation and extraction with more balanced charge carrier mobilities. More importantly, the photovoltaic performance of the ternary SM‐OSCs possesses a high tolerance to the device fabrication conditions, including thermal annealing treatment, and is insensitive to film thickness, which is beneficial for large‐area manufacture and future practical applications. [ABSTRACT FROM AUTHOR]

High efficiency organic solar cells (OSCs) based on A‐DA′D‐A type small molecule acceptors (SMAs) were mostly fabricated by toxic halogenated solvent processing, and power conversion efficiency (PCE) of the non‐halogenated solvent processed OSCs is mainly restricted by the excessive aggregation of the SMAs. To address this issue, we developed two vinyl π‐spacer linking‐site isomerized giant molecule acceptors (GMAs) with the π‐spacer linking on the inner carbon (EV‐i) or out carbon (EV‐o) of benzene end group of the SMA with longer alkyl side chains (ECOD) for the capability of non‐halogenated solvent‐processing. Interestingly, EV‐i possesses a twisted molecular structure but enhanced conjugation, while EV‐o shows a better planar molecular structure but weakened conjugation. The OSC with EV‐i as acceptor processed by the non‐halogenated solvent o‐xylene (o‐XY) demonstrated a higher PCE of 18.27 % than that of the devices based on the acceptor of ECOD (16.40 %) or EV‐o (2.50 %). 18.27 % is one of the highest PCEs among the OSCs fabricated from non‐halogenated solvents so far, benefitted from the suitable twisted structure, stronger absorbance and high charge carrier mobility of EV‐i. The results indicate that the GMAs with suitable linking site would be the excellent candidates for fabricating high performance OSCs processed by non‐halogenated solvents. [ABSTRACT FROM AUTHOR]

PM6 is a widely used D–A copolymer donor in the polymer solar cells (PSCs). Incorporating second electron‐withdrawing (A2) units into PM6 backbone by ternary D–A1–D–A2 random copolymerization strategy is an effective approach to further improve its photovoltaic performance. Here, the authors synthesize the PM6‐based terpolymers by introducing thiazolothiazole as the A2 units connecting with thiophene π‐bridges attaching alkyl substituent towards the A2 unit (PMT‐CT) or towards D‐unit (PMT‐FT), and study the effect of the alkyl substituent position on the photovoltaic performance of them. Two terpolymers PMT‐FT‐10 and PMT‐CT‐10 are obtained by incorporating 10% A2 units in the terpolymers. The film of PMT‐CT‐10 shows slightly up‐shifted highest occupied molecular orbital (HOMO) energy levels while better co‐planar structure than that of PMT‐FT‐10. Meanwhile, the PMT‐CT‐10:Y6 blend film exhibits better molecular packing properties, more proper phase separation and more balanced hole and electron mobilities, which are beneficial to more efficient exciton dissociation, efficient charge transport and weaker bimolecular recombination. Consequently, the PMT‐CT‐10 based PSCs obtain the highest power conversion efficiency of 18.21%. The results indicate that side chain position on the thiophene π‐bridges influence the device performance of the terpolymer donors, and PMT‐CT‐10 is a high efficiency polymer donor for the PSCs. [ABSTRACT FROM AUTHOR]

Tandem organic solar cell (TOSC), composed of the front and rear cells with complementary absorption, is effective device structure for surpassing the Shockley–Queisser limit of single‐junction organic solar cells (OSCs). However, most of the medium bandgap (≈1.6 eV) organic photovoltaic materials for front cells in the TOSCs show considerable voltage losses. In this work, two medium bandgap (1.63 eV) isomeric small molecule acceptors m‐DTC‐Cl‐1 and m‐DTC‐Cl‐2 are synthesized with different chlorine substitution positions in 2‐(3‐oxo‐2,3‐dihydroinden‐1‐ylidene)malononitrile (IC). The different chlorine substituted positions in IC groups show significant influences on the physicochemical properties, charge dynamics, morphology, and photovoltaic performance of the acceptors. Consequently, the OSC with PTO2 as polymer donor and m‐DTC‐Cl‐2 as acceptor delivers a champion power conversion efficiency (PCE) of 14.1% with a high open circuit voltage of 1.05 V and a low nonradiative energy loss of 0.25 eV, which indicates that the OSC is an ideal candidate for the application as front cell in the TOSCs. Then, a monolithic TOSC is fabricated with the OSC based on PTO2:m‐DTC‐Cl‐2 as front cell and the OSC based on PTB7‐Th:BTPV‐4Cl as rear cell, which demonstrates a high PCE of 18.8%. [ABSTRACT FROM AUTHOR]

Recently, a random ternary copolymerization strategy has become a promising and efficient approach to develop high‐performance polymer donors for polymer solar cells (PSCs). In this study, a low‐cost electron‐withdrawing unit, 2,5‐bis(4‐(2‐ethylhexyl)thiophen‐2‐yl)pyrazine (PZ‐T), is incorporated into the polymer backbone of PM6 as the third component, and three D‐A1‐D‐A2 type terpolymers PMZ‐10, PMZ‐20, and PMZ‐30 are synthesized by the random copolymerization strategy, with the PZ‐T proportion of 10%, 20%, and 30%, respectively. The terpolymers exhibit downshifted highest occupied molecular orbital energy levels than PM6, which is beneficial for obtaining higher open‐circuit voltage (Voc) of the PSCs with the polymer as a donor. Importantly, the PSCs based on PMZ‐10:Y6 demonstrate efficient exciton dissociation, higher and balanced electron/hole mobilities, desirable aggregation, and high power conversion efficiency of 18.23%, which is the highest efficiency among the terpolymer‐based PSCs so far. The results indicate that the ternary copolymerization strategy with PZ‐T as the second A‐unit is an efficient approach to further improve the photovoltaic performance and reduce the synthetic cost of the D‐A copolymer donors. [ABSTRACT FROM AUTHOR]

Organic solar cells (OSCs) have recently reached a remarkably high efficiency and become a promising technology for commercial application. However, OSCs with top efficiency are mostly processed by halogenated solvents and with additives that are not environmentally friendly, which hinders large‐scale manufacture. In this study, high‐performance tandem OSCs, based on polymer donors and two small‐molecule acceptors with different bandgaps, are fabricated by solution processing with non‐halogenated solvents without additive. Importantly, the two active layers developed from non‐halogenated solvents show better phase segregation and charge transport properties, leading to superior performance than halogenated ones. As a result, a tandem OSC with high efficiency of up to 16.67% is obtained, showing unique advantages in future massive production. [ABSTRACT FROM AUTHOR]

Demonstrated in this work is a simple random ternary copolymerization strategy to synthesize a series of polymer acceptors, PTPBT‐ETx, by polymerizing a small‐molecule acceptor unit modified from Y6 with a thiophene connecting unit and a controlled amount of an 3‐ethylesterthiophene (ET) unit. Compared to PTPBT of only Y6‐like units and thiophene units, PTPBT‐ETx (where x represents the molar ratio of the ET unit) with an incorporated ET unit in the ternary copolymers show up‐shifted LUMO energy levels, increased electron mobilities, and improved blend morphologies in the blend film with the polymer donor PBDB‐T. And the all‐polymer solar cell (all‐PSC) based on PBDB‐T:PTPBT‐ET0.3 achieved a high power conversion efficiency over 12.5 %. In addition, the PTPBT‐ET0.3‐based all‐PSC also exhibits long‐term photostability over 300 hours. [ABSTRACT FROM AUTHOR]

Herein, PC71BM is used as the third component (the second acceptor) to improve the photovoltaic performance of the organic solar cells (OSCs) based on a low‐cost polymer donor PTQ10 and a nonfullerene small‐molecule acceptor Y6. The ternary OSCs based on PTQ10:Y6:PC71BM reach a higher power conversion efficiency (PCE) of 16.07% with enhanced short‐circuit current density and a better fill factor in comparison with the binary OSCs based on PTQ10:Y6, which is ascribed to the higher electron mobility, better charge extraction, and suppressed charge recombination of the ternary PSCs. The film morphology of the OSCs is studied by grazing‐incidence wide‐angle X‐ray scattering, photo‐induced force microscopy, and transmission electron microscopy, which reveals that with the treatment of additive (0.5% CN) and thermal annealing, the phase separation of Y6 is obviously enhanced, whereas no significant changes occur for that of PTQ10 component. Besides, the addition of PC71BM slightly lowers the ratio of the face‐on orientation in the blend film and attenuate the aggregation of acceptor Y6. In addition, compared with the binary PTQ10:Y6 OSC, the ternary device based on PTQ10:Y6:PC71BM shows better device stability, demonstrating a great potential for the practical application of ternary OSCs. [ABSTRACT FROM AUTHOR]

The molecular conformation of giant molecule acceptors (GMAs) plays a significant role in regulating the intermolecular interactions and their photovoltaic performances in organic solar cells (OSCs). For the linear GMA GT‐l, the stronger homo‐molecular interaction causes its aggregation being weakly affected by the donor, thus forming an ordered molecular stacking and proper phase separation in its blend film. The star‐shaped GMA GT‐s‐based blend film shows a dominant hetero‐molecular interaction that suppresses the aggregation of the donor and acceptor, resulting in smaller phase separation and more uniform vertical phase distribution. While for another star‐shaped GMA GTs, the weakest hetero‐molecular interaction causes its blend film to form larger phase separation. Therefore, the GT‐l based OSC with PM6 as donor shows the highest charge mobilities, the fastest charge transfer (CT) process, reduced energy loss and less charge recombination, contributing to a higher power conversion efficiency (PCE) of 19.03%. Comparatively, the PCEs of the OSCs based on GTs and GT‐s are 18.05% and 17.58% respectively. Notably, all the three GMAs based OSCs show excellent thermal stability and long‐term storage stability. This study provides a facile strategy by tuning the linking unit and its connecting mode for designing highly efficient and stable organic photovoltaic materials. [ABSTRACT FROM AUTHOR]

Organic solar cells (OSCs) processed with non‐halogenated solvents usually suffer from excessive self‐aggregation of small molecule acceptors (SMAs), severe phase separation and higher energy loss (Eloss), leading to reduced open‐circuit voltage (Voc) and power conversion efficiency (PCE). Regulating the intermolecular interaction to disperse the aggregation and further improve the molecular packing order of SMAs would be an effective strategy to solve this problem. Here, we designed and synthesized two SMAs L8‐PhF and L8‐PhMe by introducing different substituents (fluorine for L8‐PhF and methyl for L8‐PhMe) on the phenyl end group of the inner side chains of L8‐Ph, and investigated the effect of the substituents on the intermolecular interaction of SMAs, Eloss and performance of OSCs processed with non‐halogenated solvents. Through single crystal analysis and theoretical calculations, it is found that compared with L8‐PhF, which possesses strong and abundant intermolecular interactions but downgraded molecular packing order, L8‐PhMe with the methyl substituent possesses more effective non‐covalent interactions, which improves the tightness and order of molecular packing. When blending the SMAs with polymer donor PM6, the differences in intermolecular interactions of the SMAs influenced the film formation process and phase separation of the blend films. The L8‐PhMe based blend film exhibits shorten film formation and more homogeneous phase separation than those of the L8‐PhF and L8‐Ph based ones. Especially, the OSCs based on L8‐PhMe show reduced non‐radiative energy loss and enhanced Voc than the devices based on the other two SMAs. Consequently, the L8‐PhMe based device processed with o‐xylene (o‐XY) and using 2PACz as the hole transport layer (HTL) shows an outstanding PCE of 19.27 %. This study highlights that the Eloss of OSCs processed with non‐halogenated solvents could be decreased through regulating the intermolecular interactions of SMAs by inner side chain modification, and also emphasize the importance of effectivity rather than intensity of non‐covalent interactions introduced in SMAs on the molecular packing, morphology and PCE of OSCs. [ABSTRACT FROM AUTHOR]