Self-boosting non-hydrolytic synthesis of Cl-passivated SnO2 nanocrystals for universal electron transport material of next-generation solar cells.

• Non-hydrolytic synthesis of SnO 2 NCs using t -BuOH improved Cl passivation and dispersibility. • t -SnO 2 effectively passivated defects at the interface between perovskite layer and ETL. • t -SnO 2 ETL-based regular (n-i-p) PSCs achieved a PCE of 20.2% and excellent device stability, maintaining 97% of initial PCE after 70 days. • t -SnO 2 has also been successfully applied as ETL to inverted (p-i-n) PSCs and inverted (n-i-p) OSCs. Recently, tin oxide (SnO 2) has attracted great attention as a promising electron transport layer (ETL) material for perovskite solar cells (PSCs) due to its high electron mobility, low-temperature fabrication and superior photocatalytic stability. However, there remains room for further utilization of the full potential of this material and improvement in power conversion efficiency (PCE) of devices, including establishment of controllable synthetic process and efficient surface modification. In this study, we first report on the novel tert -butyl alcohol (t -BuOH)-mediated non-hydrolytic synthesis of SnO 2 nanocrystals (NCs) with effective pre-Cl-passivation without additional treatment. In this reaction, the by-products, tert -butyl chloride and water, are readily hydrolyzed to t -BuOH and chloride ions, which can be continuously reused and boost the reaction. Consequently, Cl effectively passivates the surface of SnO 2 NCs as well as facilitates the dispersion stability, leading to reduced trap density and enhanced charge extraction characteristics of the SnO 2 ETL. The device fabricated using the t -BuOH-mediated SnO 2 NCs exhibits improved device efficiency, excellent reproducibility, reduced hysteresis, and longer device stability compared to the device using SnO 2 NCs synthesized by conventional non-hydrolytic process. For the regular type (n-i-p) PSCs, the device achieves a PCE of 20.2% and maintains 97% of initial efficiency after 70 days under ambient conditions. In addition, unnecessary high temperature annealing and additional treatment of the non-hydrolytically synthesized SnO 2 NCs enable their direct deposition on the perovskite layer, thereby leading to inverted type (p-i-n) PSCs with the best PCE of 17.0%. [ABSTRACT FROM AUTHOR]