By introducing an indium sulfate functional layer at the buried interface, In³⁺ forms a gradient doping, eliminating harmful defects through dynamic redox cycles (Pb⁰→Pb²⁺, I⁰→I⁻) to achieve synergistic bulk and interfacial healing, and leading to a high efficiency of 22.97% and excellent device stability for the ETL-free perovskite solar cells.

Abstract

Perovskite solar cells without electron transport layers (ETL-free PSCs) have garnered increasing attention in recent years due to their simplified fabrication process and low production costs. However, non-radiative recombination of charge carriers and band energy mismatch at the interface significantly limit device performance. Here, we propose an ion-mediated self-healing strategy introducing an indium sulfate (ln₂(SO₄)₃) functional layer at the buried interface of the perovskite. The ln³⁺ exhibits gradient doping at the buried interface, acting as a redox buffer to oxidize Pb⁰ to Pb²⁺, while the generated ln⁺ reduces I⁰ to I⁻, forming a self-healing redox dynamic cycle. The incorporation of indium sulfate effectively improves the contact properties and band energy alignment at the ITO/perovskite interface, ultimately achieving a high-power conversion efficiency of 22.97%. The device retains 91.6% of its initial efficiency after 1200 h of continuous illumination, providing new insights for the development and application of perovskite solar cells without electron transport layers.