Antioxidation and Energy-Level Alignment for Improving Efficiency and Stability of Hole Transport Layer-Free and Methylammonium-Free Tin-Lead Perovskite Solar Cells

Tin-lead (Sn-Pb) perovskites have shown great potential in applications of single-junction perovskite solar cells (PSCs) and tandem devices due to outstanding photoelectrical properties and low band gaps. Currently, Sn-Pb PSCs typically have a p-i-n structure, but choices of hole transport layer (HTL) materials are very limited and there are different concerns in each of them. Eliminating the HTL is a direct and promising strategy to address the concerns, but is rarely studied. In this work, we demonstrate HTL-free and MA-free based Sn-Pb PSCs and a synergistic integration strategy of simultaneously introducing a reducing agent and in situ surface passivation. With the integration strategy, Sn-Pb perovskite films with enhanced antioxidation, reduced trap density, prolonged carrier lifetime, and improved energy-level alignment are achieved. Consequently, final HTL-free PSCs exhibit a champion power conversion efficiency (PCE) of 17.4%, which is a new record for HTL-free and MA-free Sn-Pb PSCs. Meanwhile, the integration strategy-based HTL-free device maintains excellent stability with efficiency unchanged for the first 200 h, and finally retaining 81% of the efficiency after 480 h aging in the air. This study shows the potential of achieving desirable HTL-free and MA-free Sn-Pb PSCs and offers more opportunities for tandem solar cells and other photovoltaic devices.