Carrier control in Sn-Pb perovskites via 2D cation engineering for all-perovskite tandem solar cells with improved efficiency and stability

All-perovskite tandem solar cells are promising for achieving photovoltaics with power conversion efficiencies above the detailed balance limit of single-junction cells, while retaining the low cost, light weight and other advantages associated with metal halide perovskite photovoltaics. However, the efficiency and stability of all-perovskite tandem cells are limited by the Sn-Pb-based narrow-bandgap perovskite cells. Here we show that the formation of quasi-two-dimensional (quasi-2D) structure (PEA)(2)GAPb(2)I(7) from additives based on mixed bulky organic cations phenethylammonium (PEA+) and guanidinium (GA+) provides critical defect control to substantially improve the structural and optoelectronic properties of the narrow-bandgap (1.25 eV) Sn-Pb perovskite thin films. This 2D additive engineering results in Sn-Pb-based absorbers with low dark carrier density (similar to 1.3 x 10(14) cm(-3)), long bulk carrier lifetime (similar to 9.2 mu s) and low surface recombination velocity (similar to 1.4 cm s(-1)), leading to 22.1%-efficient single-junction Sn-Pb perovskite cells and 25.5%-efficient all-perovskite two-terminal tandems with high photovoltage and long operational stability.

Automated summary

This study demonstrates that the addition of mixed bulky organic cations can improve the structural and optoelectronic properties of Sn-Pb perovskite thin films, resulting in high-efficiency single-junction and all-perovskite tandem solar cells with improved stability.