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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]

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]

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]

In recent years, perovskite has been widely adopted in series-connected monolithic tandem solar cells (TSCs) to overcome the Shockley-Queisser limit of single-junction solar cells. Perovskite/organic TSCs, comprising a wide-bandgap (WBG) perovskite solar cell (pero-SC) as the front cell and a narrow-bandgap organic solar cell (OSC) as the rear cell, have recently drawn attention owing to the good stability and potential high power conversion efficiency (PCE) 1,2,3,4 . However, WBG pero-SCs usually exhibit higher voltage losses than regular pero-SCs, which limits the performance of TSCs 5,6 . One of the major obstacles comes from interfacial recombination at the perovskite/C 60 interface, and it is important to develop effective surface passivation strategies to pursue higher PCE of perovskite/organic TSCs 7 . Here we exploit a new surface passivator cyclohexane 1,4-diammonium diiodide (CyDAI 2 ), which naturally contains two isomeric structures with ammonium groups on the same or opposite sides of the hexane ring (denoted as cis-CyDAI 2 and trans-CyDAI 2 , respectively), and the two isomers demonstrate completely different surface interaction behaviors. The cis-CyDAI 2 passivation treatment reduces the Quasi-Fermi level splitting (QFLS)-open circuit voltage (V oc ) mismatch of the WBG pero-SCs with a bandgap of 1.88 eV and enhanced its V oc to 1.36 V. Combining the cis-CyDAI 2 treated perovskite and the organic active layer with a narrow-bandgap of 1.24 eV, the constructed monolithic perovskite/organic TSC demonstrates a PCE of 26.4% (certified as 25.7%)., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

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., (© 2023 Wiley-VCH GmbH.)

PM6 is a widely used D-A copolymer donor in the polymer solar cells (PSCs). Incorporating second electron-withdrawing (A 2 ) units into PM6 backbone by ternary D-A 1 -D-A 2 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 A 2 units connecting with thiophene π-bridges attaching alkyl substituent towards the A 2 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% A 2 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., (© 2022 The Authors. Advanced Science published by Wiley-VCH GmbH.)