Developing all‐perovskite tandem solar cells has been proved to be an effective approach to boost the efficiency beyond the Shockley–Queisser limit. However, the Sn‐based narrow‐bandgap (NBG) perovskite solar cells (PSCs) suffer from the relatively low photostability, which limits their further application in all‐perovskite tandem solar cells. In this work, the instability of NBG PSCs is found to come from the commonly used acidic hole transporting material PEDOT:PSS, which reacts with the indispensable basic additive SnF2 in the perovskite layer. By acidity control of PEDOT:PSS via aqueous ammonia, the NBG PSCs yield an efficiency of 22.0% with much improved photostability, which can maintain 91.3% of the initial value after 800 h illumination under AM 1.5G. As an application, the corresponding all‐perovskite tandem cells exhibit a stabilized efficiency of 25.3% with 92% remaining after 560 h illumination. This work reveals an origin of instability of NBG PSCs and provides an effective approach to enhance the device stability, which can promote the development of all‐perovskite tandem solar cells.

The green hydrogen economy is expected to play a crucial role in carbon neutrality, but industrial-scale water electrolysis requires improvements in efficiency, operation costs, and capital costs before broad deployment. Electrolysis operates at a high current density and involves the substantial formation of gaseous products from the electrode surfaces to the electrolyte, which may lead to additional resistance and a resulting loss of efficiency. A detailed clarification of the bubble departure phenomena against the electrode surface and the surrounding electrolytes is needed to further control bubbles in a water electrolyzer. This study clarifies how electrolyte properties affect the measured bubble detachment sizes from the comparisons with analytical expressions and dynamic simulations. Bubble behavior in various electrolyte solutions and operating conditions was described using various physical parameters. A quantitative relationship was then established to connect electrolyte properties and bubble departure diameters, which can help regulate the bubble management through electrolyte engineering.