A Ferrocene Capping Layer Enabling Highly Efficient and Stable Sn-Pb Mixed Perovskite Solar Cells

The Sn-Pb mixed perovskite with a narrow bandgap is essential for the construction of all-perovskite tandem solar cells. However, the oxidation of Sn2+ to Sn4+ makes the fabrication of Sn-Pb perovskite solar cells (PSCs) challenging. Herein, a ferrocene (Fc) capping layer is introduced on the surface of Sn-Pb mixed perovskite to maintain a reducing environment. This is due to a strong electron supply capacity from the pi-orbitals in cyclopentadiene in Fc, which effectively suppresses the oxidation of Sn2+, reduces the defect density, and leads to an improvement in carrier lifetime. Therefore, the Fc capping layer significantly improves the power conversion efficiency (PCE) of single-junction Sn-Pb PSCs from 17.49% to 21.02%. It maintains 87% of its initial PCE after light exposure at 1 sun condition in N2 atmosphere for 288 h, demonstrating good long-term stability. The strategy outlined herein offers a straightforward and efficient approach to enhance the stability and PCE of narrow-bandgap Sn-Pb mixed PSCs. Herein, a ferrocene capping layer is introduced on the surface of Sn-Pb perovskite to maintain a reducing environment. This approach significantly improves the power conversion efficiency (PCE) from 17.49% to 21.02% and maintains 87% of its initial PCE after light exposure at 1 sun conditions in an N2 atmosphere for 288 h.image (c) 2024 WILEY-VCH GmbH