Oriented molecular modulation of SnO2 nanoparticles enabled bilateral passivation toward efficient and stable perovskite solar cells

Tin oxide has emerged as a promising electron transport material in perovskite solar cells due to its high conductivity and photostability. However, the inherent defects in SnO 2 nanoparticles and their imperfect bonding with perovskite at the interface lead to additional energy loss. To achieve bifacial passivation on the SnO 2 electron transporting layer and the SnO 2 /perovskite interface synchronously, a multifunctional surface modulation strategy has been developed by incorporating O-phospho-L-serine monolithium salt (PS-Li) to regulate the SnO 2 nanoparticles. PS-Li coordinates with SnO 2 through the phosphate/carboxyl groups, with the exposed amino group passivating the uncoordinated lead ions at the interface. The introduction of a lithium ion further regulates the energy band of SnO 2 , accelerating electron extraction and transport. This multifunctional modulation reduces trap states from tin dangling bonds and oxygen vacancies, enhancing film conductivity. It also regulates the growth of the perovskite crystal and reduces nonradiative recombination at the interface. Consequently, the optimized perovskite solar cells achieve power conversion efficiencies (PCEs) of 24.91% for small-area devices and 23.14% for mini-modules (aperture area of 30 cm 2 ). The unencapsulated device retains 91% and 89% of its initial PCE after enduring 1000 h under ambient conditions, and 500 h under 1 sun illumination in N 2 atmosphere, respectively.