Strain Control of Mixed‐Halide Wide‐Bandgap Perovskites for Highly Efficient and Stable Solar Cells

Mixed‐halide perovskites with wide‐bandgap (WBG) have been widely applied for tandem solar cells. Nevertheless, WBG perovskite solar cells (PSCs) easily suffer from photo‐induced phase segregation, deteriorating their device efficiency and stability. It is a desirable way that the suppression of phase segregation from the strain relaxation in mixed‐halide WBG perovskite films. Herein, p‐toluene sulfonate (p‐TS) can effectively release the residual strain in WBG perovskite films by occupying the empty orbitals of the uncoordinated Pb 2+ and halide ion vacancies, as well as improving the crystallinity and passivating the defect states. The outcomes of this strain relaxation are observed to be highly effective in inhibiting phase segregation in WBG perovskite films. Based on the WBG perovskite with p‐TS, the significantly improved power conversion efficiency (PCE) of 21.12% is accomplished with the lowest open‐circuit voltage deficits (410 mV) for the n‐i‐p PSCs with an optical bandgap of 1.66 eV. And satisfactory stability of PSC has been gained; the encapsulated device maintains efficiency over 82% of the original efficiency after 1000 h continuous illumination (1‐Sun, ≈40 °C). Besides, the p‐TS PSC maintains 98.9% of the initial PCE after 4000 h storage in the dry condition (≈10%–20% relative humidity, ≈30 °C).