Unraveling Device Physics of Dilute‐Donor Narrow‐Bandgap Organic Solar Cells with Highly Transparent Active Layers

Abstract The charge generation–recombination dynamics in three narrow‐bandgap near‐IR absorbing nonfullerene (NFA) based organic photovoltaic (OPV) systems with varied donor concentrations of 40%, 30%, and 20% are investigated. The dilution of the polymer donor with visible‐range absorption leads to highly transparent active layers with blend average visible transmittance (AVT) values of 64%, 70%, and 77%, respectively. Opaque devices in the optimized highly reproducible device configuration comprising these transparent active layers lead to photoconversion efficiencies (PCEs) of 7.0%, 6.5%, and 4.1%. The investigation of these structures yields quantitative insights into changes in the charge generation, non‐geminate charge recombination, and extraction dynamics upon dilution of the donor. Lastly, this study gives an outlook for employing the highly transparent active layers in semitransparent organic photovoltaics (ST‐OPVs).