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Impressive advancements in solution‐processed bulk heterojunction (BHJ) solar cells have been driven to a large extent by the rational design of conjugated polymers as photoactive donors. These achievements have been obtained without paying much attention to green metrics parameters (such as E factor) and to the increasing synthetic complexity (SC), which is a bottleneck for industrial scalability. In this context, a novel donor copolymer (PBDT3T) based on benzodithiophene and terthiophene building blocks with ester functionalities is synthesized. The 26‐fold‐reduced E factor for the benzodithiophene monomer synthesis and the SC index of 24 for PBDT3T, much lower compared with benchmark donor polymers, provide a hint for good scalability, sustainability, and low costs. PBDT3T features a relatively wide optical bandgap and a deep highest occupied molecular orbital (HOMO), meeting the requirements for suitable donor material in both fullerene and nonfullerene‐based solar cells. PBDT3T is studied in binary and ternary blend, using PC71BM and ITIC as acceptors. The best performances are obtained in the ternary blend devices, reaching power conversion efficiency (PCE) values of 7.14%. Trade‐off considerations between PCE and SC make PBDT3T promising on an industrial perspective.

Abstract Significant progress has been made in nonfullerene small molecule acceptors (NF‐SMAs) that leads to a consistent increase of power conversion efficiency (PCE) of nonfullerene organic solar cells (NF‐OSCs). To achieve better compatibility with high‐performance NF‐SMAs, the direction of molecular design for donor polymers is toward wide bandgap (WBG), tailored properties, and preferentially ecofriendly processability for device fabrication. Here, a weak acceptor unit, methyl 2,5‐dibromo‐4‐fluorothiophene‐3‐carboxylate (FE‐T), is synthesized and copolymerized with benzo[1,2‐b:4,5‐b′]dithiophene (BDT) to afford a series of nonhalogenated solvent processable WBG polymers P1‐P3 with a distinct side chain on FE‐T. The incorporation of FE‐T leads to polymers with a deep highest occupied molecular orbital (HOMO) level of −5.60−5.70 eV, a complementary absorption to NF‐SMAs, and a planar molecular conformation. When combined with the narrow bandgap acceptor ITIC‐Th, the solar cell based on P1 with the shortest methyl chain on FE‐T achieves a PCE of 11.39% with a large Voc of 1.01 V and a Jsc of 17.89 mA cm−2. Moreover, a PCE of 12.11% is attained for ternary cells based on WBG P1, narrow bandgap PTB7‐Th, and acceptor IEICO‐4F. These results demonstrate that the new FE‐T is a highly promising acceptor unit to construct WBG polymers for efficient NF‐OSCs.

[Display omitted] • We constructed a new type of intrinsically stretchable active layer. • We synergistic optimized the mechanical and photovoltaic properties of OPV film. • We successfully predicted the changes in elastic modulus of the blend film. In recent years, the power conversion efficiency of all-polymer organic photovoltaic cells (OPVs) has surpassed 19%, reaching a level suitable for commercial applications. To meet the dual requirements of high efficiency and high stretchability for wearable applications, ternary blending strategies have been widely used to improve the tensile properties of all-polymer OPVs. However, up to now, synergistic optimization of both photovoltaic and mechanical properties has seldom been realized. Herein, we introduce a long-branched side chain-containing PM6-like donor polymer, PM6-OD, into a PM6:PY-IT blend to construct stretchable active layers for all-polymer OPVs. When the weight content of PM6-OD in the donor polymers is 20%, both the photovoltaic and mechanical properties of the ternary solar cell are maximized. The variation of the mechanical and photovoltaic properties with the PM6-OD content in the donor was analyzed through grazing-incidence X-ray scattering and thin-film mechanical measurements to gain a deeper understanding of the intrinsic relationship between blend microstructure and mechanical properties. In addition, we prove that the data points of elastic moduli match well with the Kerner-Davis model. This work provides new guidance for the construction of high-efficiency, stretchable OPVs and has a promoting effect on the application of OPVs in wearable/stretchable electronics. [ABSTRACT FROM AUTHOR]

Significant progress has been made in nonfullerene small molecule acceptors (NF‐SMAs) that leads to a consistent increase of power conversion efficiency (PCE) of nonfullerene organic solar cells (NF‐OSCs). To achieve better compatibility with high‐performance NF‐SMAs, the direction of molecular design for donor polymers is toward wide bandgap (WBG), tailored properties, and preferentially ecofriendly processability for device fabrication. Here, a weak acceptor unit, methyl 2,5‐dibromo‐4‐fluorothiophene‐3‐carboxylate (FE‐T), is synthesized and copolymerized with benzo[1,2‐b:4,5‐b′]dithiophene (BDT) to afford a series of nonhalogenated solvent processable WBG polymers P1‐P3 with a distinct side chain on FE‐T. The incorporation of FE‐T leads to polymers with a deep highest occupied molecular orbital (HOMO) level of −5.60−5.70 eV, a complementary absorption to NF‐SMAs, and a planar molecular conformation. When combined with the narrow bandgap acceptor ITIC‐Th, the solar cell based on P1 with the shortest methyl chain on FE‐T achieves a PCE of 11.39% with a large Voc of 1.01 V and a Jsc of 17.89 mA cm−2. Moreover, a PCE of 12.11% is attained for ternary cells based on WBG P1, narrow bandgap PTB7‐Th, and acceptor IEICO‐4F. These results demonstrate that the new FE‐T is a highly promising acceptor unit to construct WBG polymers for efficient NF‐OSCs. [ABSTRACT FROM AUTHOR]