Multifunctional Engineering-Enabled Electron Transport in SnO₂ for Sn-Based Perovskite Solar Cells in the n-i-p...

The two-step sequential deposition technique reported in the inverted p-i-n configuration to fabricate Sn perovskite solar cells fails in the TiO₂-based n-i-p configuration since the latter aggravates Sn²⁺ oxidation from the SnI₂ nucleation layer upon pore infiltration. However, ambipolar SnO₂ only promotes hole transport in Sn perovskite. Here, we report Cl-doped SnO₂ (Cl:SnO₂) with surface functionalities using multifunctional polybenzoxazine (p-Benz) to circumvent the SnO₂/SnI₂ interfacial redox reaction that would otherwise amplify hole extraction. The p-Benz functionalization altered the photoemissive properties of the transparent electrode and introduced a small charge transport resistance against undesirable carrier leakage toward the ETL side by simultaneously enabling contact establishment in the dark. When illuminated, the hole-rich Sn perovskite in contact with the PTAA hole-transport layer allows rapid hole injection, which induces an internal electric field, leading to a functioning planar n-i-p device. By integrating the two-step method in the n-i-p configuration and facilitating selective electron transport in SnO₂, the versatility in device engineering is uncovered.