Performance Constraints of All‐Perovskite Tandem Solar Cells in Low‐Intensity, Low‐Temperature Environments

All-perovskite tandem solar cells (2J-PSCs) reach the highest power-to-weight ratios, making them promising candidates for space applications. To determine their potential for future deep space missions, this study assesses the performance of 2J-PSCs under low-intensity and low-temperature (LILT) conditions, akin to those found near Saturn, the Asteroid belt, or in eclipse. Temperature-dependent current density-voltage (J-V) measurements under varying solar intensities (AM0, 0.1 AM0, 0.01 AM0) reveal that the 2J-PSCs, comprising 1.80 eV high-bandgap and 1.27 eV low-bandgap perovskites, exhibit significant efficiency losses at lower temperatures and low light levels. In contrast, 1.54 eV single-junction PSCs (1J-PSCs) exhibit resilient performance, maintaining or even increasing their power conversion efficiency at low temperatures. The main performance problem of the 2J-PSCs is then identified as a demixing of the 1.80 eV perovskite due to its high Br ratio at temperatures below 250 K. This demixing at low temperatures leads to a significant increase in ion-induced performance losses as well as current imbalances between the two subcells in the monolithic tandem. Together, this causes severe S-shapes in solar cell operation and impedes the operation of the monolithic interconnected tandem solar cells. Notably, these limitations vanish upon heating, leading to a recovery of performance.