F-Type Pseudo-Halide Anions for High-Efficiency and Stable Wide-Band-Gap Inverted Perovskite Solar Cells with Fill Factor Exceeding 84%

The quality of wide-band-gap (WBG) perovskite films plays an important role in tandem solar cells. Therefore, it is necessary to improve the performance of WBG perovskite films for the development of tandem solar cells. Here, we employ F-type pseudo-halogen additives (PF6- or BF4-) into perovskite precursors. The perovskite films with F-type pseudo-halogen additives have a larger grain size and higher crystal quality with lower defect density. At the same time, the perovskite lattice increases due to substitution of F-type pseudo-halogen anions for I-/Br-, and the stress distortion in the film is released, which effectively suppresses the recombination of carriers, reduces the charge transfer loss, and inhibits the phase separation. Finally, the power conversion efficiency (PCE) of the inverted 1.67 eV perovskite devices is significantly improved to over 20% with an impressive fill factor of 84.02% and excellent device stability. In addition, the PCE of the four-terminal (4T) perovskite/silicon tandem solar cells reached 27.35% (PF6-) and 27.11% (BF4-), respectively. This provides important guidance for further improving WBG perovskite solar cell performance.