Side-Chain Engineering of Y-Series Acceptors with Halogenated End-Group for Efficient Indoor Organic Photovoltaics

Diverse design strategies for nonfullerene acceptors (NFAs) have aided the development of efficient indoor organic photovoltaics (OPVs) for Internet-of-things-enabled gadgets. However, the side-chain approach to Y-series NFAs for fabricating indoor OPVs remains largely unexplored. In this study, the synthesis and photovoltaic characteristics of two side-chain engineered NFAs with halogenated end-groups (BTP-PO-4F and BTP-PO-4Cl) are investigated. NFAs with a Y6 core unit are modified with butyloctyl inner side chains and ethylhexyloxynaphthyl outer side chains. The extended conjugation moiety contributed to red-shifted absorption, with the chlorination effect presenting a more pronounced influence than fluorination. Further, the outer moiety introduced a slight electron-withdrawing effect on the Y6 core unit, resulting in energy-level downshifts. An excellent power conversion efficiency (PCE) of 23.2% is achieved in fluorinated OPVs under a light-emitting diode lamp (1000 lux). Moreover, integrating the Y6 NFA into the binary blend further enhanced the PCE, reaching 28.3% in PM6:Y6:halogenated NFA ternary OPVs. The panchromatic absorption, high crystallinity, and cascaded energy levels of the ternary blends contribute to achieving a sufficient spectral match and suppress trap-assisted recombination, ultimately fostering a substantially enhanced fill factor and PCEs under indoor lighting. This study explores side-chain engineering for non-fullerene acceptors (NFAs) in indoor organic photovoltaics. Two NFAs, BTP-PO-4F and BTP-PO-4Cl, are synthesized, leading to a red-shifted absorption and improved energy-level alignment. The study achieved a remarkable 23.2% power conversion efficiency in fluorinated OPVs under LED lighting, which increased to 28.3% in ternary OPVs with PM6:Y6:halogenated NFA blends, enhancing PCE under indoor lighting.image