Air processed, high open-circuit voltage indoor organic photovoltaic cells based on side chain modified N-annulated perylene diimides

To achieve high-performance indoor organic photovoltaics (OPVs), it is important to match the photoactive layer optical absorption with the light-source emission. This can be accomplished by developing organic photoactive materials that can efficiently absorb visible light and thus minimize energy losses. While indoor OPVs have achieved efficiencies above 33% under low light intensities, the power output is limited by low open circuit voltages (V_OC), often well below 1 V. In this study, we present a series of visible-light absorbing (energy gap >1.90 eV) non-fullerene acceptors (NFAs) based on perylene diimide dimers, which have been systematically modified with side chains of varying polarity and steric bulk (trimethyl benzyl, ethyl adamantane, trialkoxyl phenyl, and oligo ethylene glycol). Our results show that the incorporation of sterically bulky side chains such as ethyl adamantane and trimethyl benzyl, blended with the common widegap polymer PTQ10, provides photoactive layers with absorption greater than 2.0 eV, and consequently, V_OCs higher than 1.2 V are achieved under AM 1.5 G illumination. Importantly, we found that the NFA with ethyl adamantane based side chains (tPDI₂N-ethyl adamantane, compound 4) exhibited the best performance, with minimized energy loss. As a result, devices using PTQ10:tPDI₂N-ethyl adamantane photoactive layers demonstrated excellent indoor efficiencies of over 16% and 18 μW cm⁻² power output under a 2700 K LED lamp at 300 lux, and showed better repeatability compared to other systems. The PTQ10:tPDI₂N-ethyl adamantane based devices maintained a high V_OC (>1.0 V) across a wide range of indoor lighting conditions, including 2700 K and 6500 K LED lamps. Overall, this work provides a sidechain engineering method to create NFAs for efficient indoor OPV devices.