Molecular Buffering Regulates Lattice Strain for Fatigue‐Resistant Perovskite Photovoltaics Under Cryogenic Thermal Cycling

Operational stability of perovskite solar cells (PSCs) under temperature fluctuations poses a critical challenge for their practical application in extreme environments such as polar and aerospace regions. Although they exhibit commendable low-temperature performance, the operational degradation mechanism under cryogenic thermal cycling remains unknown. Here, we uncover a mechanochemical fatigue process wherein cycling between 173 and 298 K generates irreversible structural injury and deep-level traps through cumulative lattice strain, rather than chemical decomposition. To address this, we design a π-conjugated molecular buffer, (methylsulfonyl)benzamidine (MSMC), which dissipates cumulative lattice strain under cryogenic thermal cycling via a chemical bonding network while simultaneously healing crystallographic defects through bidentate lead coordination. This synergistic strategy endows p-i-n devices that achieve a record efficiency of 28.01% at 228 K (certified 25.94% at 298 K) and, critically, demonstrate unprecedented resilience to cryogenic thermal shocks, retaining 90% of their initial performance after 260 cycles, nearly threefold improvement over controls. The strategy also provides robust compatibility with standard ISOS protocols (light, heat, humidity), underscoring their broad operational resilience. This work establishes mechanochemical fatigue as a fundamental degradation mode and provides a molecular-scale methodology for creating robust photovoltaics suitable for widespread applications.