Regulating the Donor–Acceptor Interfaces to Reduce Trap Density for Efficient Indoor Organic Solar Cells

Organic solar cells (OSCs) are promising candidates for powering the Internet of Things and off‐grid devices due to the rapid improvement in power conversion efficiency under indoor light. However, the reported indoor devices are often taken straightforwardly from the champion solar cells under AM1.5 G irradiance without further optimization or more target design, which may underestimate their performance due to trap‐assisted charge recombination caused by discrepancies in incident light spectrum and intensity. Herein, It is identified that regulation of donor–acceptor interfaces is critical for reducing trap density in the active layer and thus improving the performance of indoor OSCs. By investigating bulk heterojunction and bilayer devices composed of PM6 and ITIC or ITIC‐2 F, reduced trap density is demonstrated by mitigation of the structural disorder of the active layer, leading to improved open‐circuit voltage. Additionally, the trap depth has a negligible effect on the device's performance with indoor light illumination. The results establish the correlations between donor–acceptor interfaces and charge recombination losses in bulk heterojunction and bilayer OSCs under indoor light, providing novel optimization guidelines for high‐performing indoor OSCs.