Sub-sized monovalent alkaline cations enhanced electrical stability for over 17% hysteresis-free planar perovskite solar mini-module

Although high efficiencies have been achieved for perovskite solar cells (PSCs), stability issues are still the key barriers for commercial applications. Herein, we carry out a systematic doping of non-radiative alkaline metal ions (Cs, Rb, K, Na, Li) to perovskite, studying their effects on perovskite morphology, electrical stability and performance of PSCs. The hysteresis related stability issues are also investigated at different conditions, such as steady-state power output, aging, repeated voltage sweeping, varied pre-scan voltage bias, etc. It is found the hysteresis becomes much severer at different test conditions for the devices doped with small sized Li and Na. While the subsized Rb and K ions (compared to Cs) doping can significantly enhance the crystallinity of perovskite and reduce the hysteresis that is also more stable. The crystallization, morphologies, time-resolved photoluminescence, electrochemical impedance spectroscopy were conducted to investigate the properties of the doped perovskite films to understand the relationship between the film quality and device performance. With a proper combination of Cs, Rb, K ions doping in PSCs, a high PCE over 20% is achieved with an enhanced electrical stability. Moreover, an over 17% efficiency 7 × 7 cm² perovskite solar cell module is realized by this strategy, with a certified PCE of 16.5% (aperture area of 20.78 cm²) without hysteresis.