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

Recently, Sn–Pb low‐bandgap (Eg) 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‐Eg PSCs, the development of all‐perovskite tandem solar cells is severely constrained. Herein, the performance of Sn–Pb low‐Eg (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‐Eg PSC as the bottom cell and a wide‐Eg (1.6 eV) PSC as the top cell. The best all‐perovskite 4‐T tandem solar cell shows a PCE of 23.26%.