Advancing Indoor Organic Photovoltaics: The Impact of Cl Density in Wide Bandgap Random Copolymers
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To enhance the efficiency of indoor organic photovoltaics (IOPVs), it is crucial to design active layers that match the absorption spectra with indoor light and possess deep HOMO levels to achieve high short-circuit current density (JSC) and open-circuit voltage (VOC), respectively. Herein, we present highly efficient IOPV devices based on wide bandgap random copolymers of B30T70-XCl (X=0, 2, 4, and 6), which efficiently cover the range of indoor light while decreasing HOMO levels in the order of 0, 2, 4, and 6Cl. Among them, B30T70-2Cl:PC71BM-based devices, show optimized power conversion efficiencies (PCEs) with high VOC, achieving a record-breaking PCE of 25% under fluorescent lamp conditions. Through a comprehensive study of energy levels, transient absorption spectroscopy, and morphology, we reveal that increasing Cl density decreases the HOMO offset, critically impacting the performance of IOPVs by influencing the population of charge-separated states.