Humidity-Regulated Wetting of Aqueous PEDOT:PSS Enables Surfactant-Free Hole-Transport Layers in Non-Fullerene-Based Inverted Organic Photovoltaics

Abstract Inverted organic photovoltaics (OPVs) feature operational stability; however, developing fully solution-processed devices remains challenging due to the poor wettability of PEDOT:PSS hole-transport layers (HTLs) on hydrophobic donor:acceptor bulk heterojunction active layers. Here, we demonstrate a surfactant-free, humidity-regulated spin-coating strategy for forming uniform PEDOT:PSS HTLs directly on PM6:Y6 active layers. By maintaining the relative humidity at 10% or lower during coating, continuous PEDOT:PSS films were obtained, enabling inverted OPVs with power conversion efficiency (PCE) above 14.5%. Furthermore, these devices retain over twice the PCE of molybdenum oxide-based devices after 100 h of light soaking under nitrogen. Bulk quantum efficiency analysis suggests that the acidic aqueous PEDOT:PSS dispersion may partially perturb the interface on the active layer, whereas it improves the overall device stability. This humidity-regulated coating approach provides a simple route toward solution-processable HTL integration in efficient and operationally stable inverted OPVs.