Stability of Sn-Pb mixed organic–inorganic halide perovskite solar cells: Progress, challenges, and perspectives

The exploration of low bandgap perovskite material to approach Shockley-Queisser limit of photovoltaic device is of great significance, but it is still challenging. During the past few years, tin–lead (Sn-Pb) mixed perovskites with low bandgaps have been rapidly developed, and their single junction solar cells have reached power conversion efficiency (PCE) over 21%, which also makes them ideal candidate as low bandgap sub-cell for tandem device. Nevertheless, due to the incorporation of unstable Sn²⁺, the stability issue becomes the vital problem for the further development of Sn-Pb mixed perovskite solar cells (PSCs). In this review, we are dedicated to give a full view in current understanding on the stability issue of Sn-Pb mixed perovskites and their PSCs. We begin with the demonstration on the origin of instability of Sn-Pb mixed perovskites, including oxidation of Sn²⁺, defects, and interfacial layer induced instability. Sequentially, the up-to-date developments on the stability improvement of Sn-Pb mixed perovskites and their PSCs is systematically reviewed, including composition engineering, additive engineering, and interfacial engineering. At last, the current challenges and future perspectives on the stability study of Sn-Pb mixed PSCs are discussed, which we hope could promote the further application of Sn-Pb mixed perovskites towards commercialization.