Volatilization‐Kinetics‐Dictated Crystallization Enabling Efficient Perovskite/Silicon Tandem Solar Cells for Near‐Space Environment

The remarkable progress in metal halide perovskite solar cells (PSCs) has propelled perovskite/silicon tandem architectures as a transformative solution in photovoltaics, enabling efficiencies beyond single‐junction limits while offering high specific power and radiation resistance for challenging environments, including near‐space and aerospace applications. Wide‐bandgap (WBG) perovskites on textured silicon, however, encounter hurdles in controlled crystallization and halide phase stability, leading to recombination losses and reduced performance. This work investigates additive engineering using volatile alkylammonium chlorides with tailored alkyl chain lengths to fine‐tune volatilization kinetics. By strategically slowing down the volatilization rate, the additive promotes homogeneous nucleation and retards grain growth, which is critical for achieving uniform perovskite coverage over the intricate topography of textured silicon substrates.​ An optimized additive promotes dense, oriented films with suppressed segregation, culminating in tandem solar cells boasting a power conversion efficiency (PCE) of 31.1% and stability exceeding 1000 h. First‐ever flight test measurements and calibrations of perovskite/silicon tandem solar cells were conducted under near‐space conditions at altitudes reaching 37.29 km. These advancements may contribute to the development of robust tandem devices for various application settings.