All-SnO₂-Based Conformal Electron Transport Layer for Efficient Perovskite Solar Cells

The fabrication of high-performance perovskite solar cells on high-haze fluorine-doped tin oxide (FTO) substrates with superior light-trapping capabilities necessitates a highly conformal electron transport layer at the bottom interface. Herein, a conformal low-temperature processable all-SnO₂-based electron transport layer (ETL) is successfully developed on high-haze FTO by well-anchoring a polyacrylic acid-stabilized quantum dot-SnO₂ layer onto an atomic layer deposited SnO₂ layer with a dense hydroxyl surface. The obtained ETL demonstrates excellent capabilities in simultaneously homogenizing the surface contact potential distribution, blocking hole transport, and suppressing non-radiative recombination. Consequently, a champion device is achieved that delivers a remarkable power conversion efficiency (PCE) of up to 24.97%, with V_OC × FF reaching 87.09% of the Shockley-Queisser limit at a bandgap of 1.54 eV, which is the highest value among the ALD SnO₂-based PSCs. The homogeneous ETL further enabled the fabrication of a 1 cm² PSC with a PCE of 23.18% and only a 10 mV loss in V_OC compared to smaller-area PSCs, showcasing its potential for large-scale commercial applications.