Wide-bandgap perovskite solar cells with > 1.34 V V_oc for all-perovskite tandems

High V_oc sub-cell is of great importance for all-perovskite tandem solar cells (PSCs). However, wide bandgap (WBG) perovskite usually suffers severe V_oc loss due to Cs-FA inhomogeneity. One key issue lies in the huge difference in crystallization temperature between Cs- and FA-based perovskite. Here, we develop a Cs-FA homogeneity strategy by shortening the difference between Cs/FA crystallization temperature with 1-propylsulfonic-3-methylimida-zolium chloride (SMCI) additive. SMCI will effectively reduce the crystallization temperature of Cs-based perovskite to 105 °C, making it simultaneously crystalized with FA-based perovskite. Resulting SMCI-based WBG PSCs (1.77 eV) achieve an efficiency of 20.03 % with high V_oc of 1.344 V. Furthermore, 2-terminal all-perovskite tandem solar cells are realized with an efficiency of 28.10 %.