Synergistic ECM-TTPBr/PCBA Dual-Molecule Buried-Interface Passivation Enables Highly Efficient Planar Carbon-Based HTL-Free Perovskite Solar Cells

This work proposed a novel strategy utilizing ethoxycarbonyl triphenylphosphonium bromide (ECM-TTPBr) as a copassivator, which significantly improves the solubility of [6,6]-phenyl-C61-butyric acid (PCBA) in chlorobenzene solution to enable uniform coverage of PCBA on the TiO₂ electron transport layer (ETL). The dual-molecule copassivation effect optimizes the interface between the ETL and perovskite layer by reducing interface defects and enhancing ETL conductivity to improve charge extraction and transport efficiency at the interface, while effectively decreasing residual lead iodide clusters at the perovskite film's bottom interface to smooth the interface and significantly improve physical contact between the perovskite layer and ETL. Owing to this dual interface passivation, the device achieves a photovoltaic conversion efficiency of 19.15% with notably enhanced stability, offering a technically feasible pathway with industrialization potential for developing high-efficiency and stable hole transport layer-free carbon-based perovskite solar cells.