Continuously graded-doped SnO₂ for efficient n–i–p perovskite solar cells

Conventional n–i–p architecture remains a robust platform for scalable perovskite photovoltaics^1,2, yet its steady-state efficiency has stagnated at about 26% (ref. ³), lagging behind their p–i–n counterparts⁴. This performance gap arises from persistent non-radiative recombination at textured electron transport layer (ETL)/perovskite interfaces, yet the underlying physical origin remains unknown. Here we show that these losses originate from the synergistic combination of band misalignment and electron accumulation at the buried interface. To address this dual challenge, we develop a continuously graded n⁺/n-doped SnO₂ ETL through a ligand-competitive binding strategy, which enables spatially defined doping that creates a built-in electric field. This graded architecture simultaneously minimizes band offset and accelerates electron extraction, thereby effectively suppressing the cross-interface recombination. The resulting n–i–p perovskite solar cells (PSCs) achieve a certified steady-state power conversion efficiency (PCE) of 27.17% (27.50% in reverse scan), the highest for n–i–p PSCs reported so far. The scalability of this strategy is further demonstrated by achieving a PCE of 25.79% for a 1 cm² device and 23.33% for a perovskite module with a 16.02 cm² aperture area. This work establishes a generalized example for energy-band engineering in metal-oxide transport layers, overcoming a fundamental efficiency bottleneck in conventional perovskite photovoltaics.