Inverted perovskite solar cells without pre-depositing a layer of hole-transport materials (HTL-free PSCs) are promising, yet currently suffer from non-irradiative recombination at the perovskite/electron-transport layer (ETL) interface. Recently, researchers from China's Southern University of Science and Technology (SUSTech) and University of Macau reported 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 retained 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.
The new molecular complementary passivation (MCP) strategy led to an obvious defect-density decrease and a more n-type perovskite surface, as was demonstrated by a series of comprehensive spectroscopy characterizations. The efficiency improvement that resulted was accompanied by a significantly improved fill factor (FF) of 86.3% and an open-circuit voltage (VOC) loss of 362 mV.
The new method could contribute to advancing HTL-free PSCs and addressing the issues holding them back.
