All-polymer solar cells based on wide bandgap polymerized non-fused electron acceptors for indoor photovoltaics

Recent studies have brought to forefront the great potential of organic solar cells (OSCs) for their merits in energy-efficient devices under diminished illumination, specifically indoor light sources. In this study, we have explored the availability of non-fused electron acceptors (NFRAs) in all-polymer solar cells (all-PSCs) for application under indoor environments. 1H-indene-1,3(2H)-dione (ID) groups have been strategically incorporated as electron-withdrawing groups to regulate the intramolecular "push-pull" effects, thereby controlling the material absorption within the visible spectra. Three distinct polymers (WP1-3) construct from NFRAs have been designed and synthesized with changing linker units (thiophene for WP1, bithiophene for WP2, and fluorinated bithiophene for WP3) in the polymerization process. The investigation has discerned the pronounced impact of different linkers on multifaceted attributes, encompassing molecular aggregation, crystallinity, phase segregation, charge-transporting property, etc. These NFRA-based polymers exhibit a high photovoltage (>1.1 V under AM1.5G and similar to 1.0 V) under indoor illumination in all-PSCs, and the best power conversion efficiency of >14% has been realized in WP2-based devices due to optimum phase separation and charge mobilities. This work sheds light on the feasibility of employing non-fused electron acceptors in all-PSCs for indoor photovoltaic applications.