Combinatorics

Electrical engineering

Saturation current

Nanotechnology

Energy conversion efficiency

Tandem

Mathematics

Crystallography

Engineering

Perovskite (structure)

Voltage

Band gap

Composite material

Halide

Inorganic chemistry

Chemistry

Metallurgy

Materials science

Layer (electronics)

Grain boundary

Passivation

Optoelectronics

Microstructure

Saturation (graph theory)

Advanced Energy Materials

The unsatisfactory performance of low‐bandgap mixed tin (Sn)–lead (Pb) halide perovskite subcells has been one of the major obstacles hindering the progress of the power conversion efficiencies (PCEs) of all‐perovskite tandem solar cells. By analyzing dark‐current density and distribution, it is identified that charge recombination at grain boundaries is a key factor limiting the performance of low‐bandgap mixed Sn–Pb halide perovskite subcells. It is further found that bromine (Br) incorporation can effectively passivate grain boundaries and lower the dark current density by two–three orders of magnitude. By optimizing the Br concentration, low‐bandgap (1.272 eV) mixed Sn–Pb halide perovskite solar cells are fabricated with open‐circuit voltage deficits as low as 0.384 V and fill factors as high as 75%. The best‐performing device demonstrates a PCE of &gt;19%. The results suggest an important direction for improving the performance of low‐bandgap mixed Sn–Pb halide perovskite solar cells.

Reducing Saturation‐Current Density to Realize High‐Efficiency Low‐Bandgap Mixed Tin–Lead Halide Perovskite Solar Cells