In-depth interfacial engineering for efficient indoor organic photovoltaics

Alternative approaches to interlayer optimization are urgently required to realize efficient indoor organic photovoltaics owing to the substantially different indoor light conditions compared to outdoor light conditions (1 sun). In this work, an in-depth study was undertaken on electron-collecting interlayers (ECIs) comprising poly-(ethyleneimine)-ethoxylated (PEIE) modification, zinc oxide (ZnO) nanoparticles (NPs), or a combination of the ZnO NPs and PEIE modification. Morphological, optical, and electrochemical properties of the ECIs were investigated using atomic force microscopy (AFM), ultraviolet-visible (UV–vis) spectrometry, and a Kelvin probe, respectively. Inverted poly(3-hexylthiophene-2,5-diyl):indene-C60 bisadduct (P3HT:ICBA)-OPVs with the ECIs were fabricated. While poor photovoltaic behavior was observed for OPVs with the ZnO NPs owing to the relatively large work function of the ECI under LED light in the absence of UV light, outstanding indoor performance was achieved by OPVs with PEIE modification as the PEIE contributed to work function reduction of the ECI. In particular, OPVs with the ZnO NPs/PEIE ECI yielded the highest efficiencies of up to 14.1 ± 0.3% under 1000-lx LED lamp.