Enhancing electron transport for efficiency -recorded HTL-free inverted perovskite solar cells by molecular complementary passivation

Inverted perovskite solar cells without pre-depositing a layer of hole-transport materials (HTL-free PSCs) still suffer from the non-irradiative recombination at the perovskite/electron-transport layer (ETL) interface. In this work, we report a molecular complementary passivation (MCP) strategy by employing propylphosphonic acid 3-ammonium bromide (PPAABr) to cooperate with phenethylammonium bromide (PEABr) to mutually passivate surface defects of I and formamidinium (FA) vacancies by multi-coordination. This passivation led to an obvious decrease in interfacial defect-state density and greatly improved exciton and carrier lifetime for the perovskite film. Moreover, MCP surface treatment pushes the perovskite surface Fermi level closer to that of ETL, thereby enhancing interfacial electron extraction. As a result, MCP-based HTL-free PSC achieved a record efficiency of 26.40% (25.92% certified). The encapsulated device retains 94.8% of its initial efficiency after 1,000 h of light soaking. The generality of the MCP strategy also generated a competitive efficiency of 23.66% for 1.68 eV wide-band-gap PSCs.