Boosted charge extraction of NbOx-enveloped SnO2 nanocrystals enables 24% efficient planar perovskite solar cells

Planar perovskite solar cells (PSCs) have attracted extensive research attention owing to their simple architecture and manufacturing process. Improving the charge extraction ability of electron transport materials (ETMs) is imperative to enhance their power conversion efficiencies (PCEs). Herein, we report low-temperature solution-processed SnO2 nanocrystals (SnO2 NCs) enveloped by amorphous NbOx (SnO2/NbOx) as efficient ETMs for planar PSCs, achieving an impressive PCE of 24.01% with negligible hysteresis, which is significantly superior to that of PSCs made from commercial SnO2 (with PCEs up to 21.96%) and self-developed SnO2 NCs (with PCEs up to 23.01%). The NbOx layer can simultaneously passivate defects at the ETMs/perovskite interface, promote charge extraction from perovskites, and improve the crystallinity of perovskite films. The unencapsulated PSC retains over 85% of its initial efficiency after 1000 h of light soaking (one sun), showing remarkable device stability. Furthermore, the low-temperature processed SnO2/NbOx ETMs are compatible with flexible substrates and present a maximum PCE of 20.00%. This work offers a facile approach to low-temperature processed ETMs with boosted carrier extraction ability, affording excellent device efficiency and stability for planar PSCs.