Highly Efficient Sn–Pb Perovskite Solar Cell and High‐Performance All‐Perovskite Four‐Terminal Tandem Solar Cell

Recently, Sn–Pb low‐bandgap ( E g ) perovskite solar cells (PSCs) have attracted enormous interest as an ideal bottom cell for all‐perovskite tandem solar cells. However, due to the lack of high‐performance Sn–Pb low‐ E g PSCs, the development of all‐perovskite tandem solar cells is severely constrained. Herein, the performance of Sn–Pb low‐ E g (1.2 eV) PSC is improved significantly using diluted poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as a hole transport layer with a maximum power conversion efficiency (PCE) up to 19.58% and short‐circuit current density of 29.81 mA cm −2 . The four‐terminal (4‐T) all‐perovskite tandem solar cell is constructed using an optical splitting system with this high‐efficient low‐ E g PSC as the bottom cell and a wide‐ E g (1.6 eV) PSC as the top cell. The best all‐perovskite 4‐T tandem solar cell shows a PCE of 23.26%.