Nonfullerene Small Molecules-Enabled High-Performance Organic Photovoltaics for Indoor Energy Harvesting

Organic photovoltaics (OPVs) have attracted considerable attention as a power source of indoor electronic devices for the Internet of Things (IoT). Herein, high-efficiency and stable nonfullerene OPVs for low-intensity indoor applications are demonstrated while discussing the origin of high photovoltaic performance and the design fundamentals in an indoor environment. Nonfullerene OPVs exhibit higher performance over a wide range of light intensities compared with fullerene OPVs, in spite of relatively lower spectral matching with indoor light sources. To understand this discrepancy, advanced morphological analyses for the bulk-heterojunction (BHJ) photoactive layers are proposed, which demonstrate efficient phase-interpenetrating networks of a polymer donor and a nonfullerene acceptor. These clarify a suppression of trap sites in nonfullerene blends as a key factor to alleviate charge recombination, resulting in high photovoltaic operation under indoor environments. Combined with the morphological benefits for the high performance, the superior stability corroborates high practical usage of nonfullerene OPVs in a variety of application areas.