Interfacial Engineering of P3HT via UV–Ozone Treatment for Indoor Perovskite Photovoltaics: Balancing Interface Quality and Charge Transport

Abstract Indoor photovoltaics (IPVs) operate under low photon flux conditions, where device performance is governed by interfacial recombination and energetic alignment rather than bulk transport. Here, a dopant-free poly(3-hexylthiophene) (P3HT) hole-transport material (HTM) is engineered via UV–ozone treatment to regulate interfacial properties in wide-bandgap perovskite IPVs. Using an equimolar I/Br FA0.85Cs0.15PbI1.5Br1.5 composition tailored for indoor bandgap requirements (Eg: 1.87 eV), moderate UV–ozone exposure enhances indoor performance (1000 lx), increasing efficiency, with improved open-circuit voltage, current density, and shunt resistance, indicating reduced interfacial recombination. Surface analyses show increased work function and surface polarity without notable morphological changes. Spectroscopic results reveal partial oxidation of sulfur moieties and formation of S–Ox species, accompanied by a broadened valence band edge and increased energetic disorder. These modifications improve interfacial energetics but degrade intrinsic charge transport. Consequently, an illumination-dependent trade-off emerges: enhanced interface quality dominates under low-light conditions, whereas transport degradation limits performance under 1 sun illumination. This study highlights that optimal HTM properties depend on operating conditions and demonstrates controlled surface oxidation as an effective strategy for IPVs.