Outer Sidechain Engineering of Selenophene and Thiophene-Based Y-Series Acceptors to Produce Efficient Indoor Organic Solar Cells

Abstract

In recent years, efficient indoor organic photovoltaics (OPVs) have emerged as promising energy harvesters to drive Internet of Nanothings (IoNT) applications. The diverse design strategies developed for non-fullerene acceptor (NFA) materials have dramatically increased the power conversion efficiency (PCE) of indoor OPVs to 31%, and progress tends to continue. In this context, the current study investigated the indoor performance of NFA-OPVs by modifying the chalcogen-containing heterocycle of the acceptor molecule to thiophene (ThTh) and selenophene (ThSe), and changing the length of the external side chain using n-hexyl (C6) and n-nonyl (C9) components. Compared with the ThSe systems, the ThTh-containing OPVs exhibited enhanced current densities (JSC) and open-circuit voltages (VOC) owing to their enhanced crystallinity and reduced degree of bimolecular recombination. Similarly, the introduction of a short side chain (i.e., C6) led to relatively reduced monomolecular recombination and a moderated planarity compared to the system modified with the long side chain (i.e., C9). Ultimately, this resulted in an enhanced JSC and improved charge transport properties. Finally, the optimized OPV exhibited a PCE of 24.6% under a 1000 lx light-emitting diode lamp.

Keywords: indoor organic photovoltaics, non-fullerene acceptor, molecular engineering, side-chain modification, Y-series acceptor