Enhanced carrier extraction and photostability in perovskite solar cells via a band-engineered Sb2Ox/TiO2 bilayer heterojunction

Abstract

Efficient electron extraction and suppression of recombination at the perovskite/electron transport layer (ETL) interface are critical for high-performance perovskite solar cells (PSCs). Heterostructured ETLs, compared to their conventional single-layer counterparts, provide enhanced charge transport through precise band edge engineering, enabling faster electron extraction and significantly reducing interfacial recombination losses. In this study, we present a bilayer heterojunction (BLH) ETL composed of antimony oxide (Sb₂O_x, where x ≈ 4.44) and titanium dioxide (TiO₂) designed to optimize charge dynamics in n–i–p structured PSCs. The lower conduction band edge of Sb₂O_x compared to TiO₂ creates a favorable cascade energy alignment that promotes efficient and unidirectional electron transport, while its deep valence band acts as an energy barrier to hole injection, effectively minimizing interfacial recombination losses. As a result, PSCs incorporating the BLH ETL achieve a champion power conversion efficiency (PCE) of 23.72%, substantially outperforming devices using TiO₂ ETLs prepared under comparable conditions. Furthermore, the strong UV-absorbing capability of the underlying Sb₂O_x layer shields the upper TiO₂ from UV-induced photocatalytic activity, thereby preventing degradation of the adjacent perovskite layer and significantly enhancing its photostability. This strategy presents a scalable and effective interface engineering approach that greatly improves charge extraction and overall device performance.