Trivalent Europium Ions Doped CsPbBr3 for Highly Efficient and Stable Printable Mesoscopic Perovskite Solar Cells and Driving Water Electrolysis

The all‐inorganic CsPbBr3 perovskite exhibits the possibility of overcoming the substantial nonideal thermal, humidity, and photostability of hybrid organic–inorganic perovskite solar cells (PSCs) in photoelectronic devices. Specifically, the rapid development of CsPbBr3 perovskite has delivered device efficiencies >10%. However, the mismatched energy band alignment and bad crystallization quality are still potential obstacles for the superior performance of PSCs. Herein, by employing n‐type doping, trivalent europium cation is successfully introduced into the CsPbBr3 lattice. The better energy‐level alignment leads to further reduction of voltage losses. Besides, the large and uniform grains resulting from the improvement of crystallization after doping decrease the grain boundaries and reduce the nonradiative recombination center. The quality of the film improves substantially, which significantly enhances the photoabsorption and the short‐circuit current density. The efficiency of the carbon‐based printable mesoscopic PSCs is improved from 7.5% to 8.06% with 3 mol% Eu3+ doping, resulting in high open‐circuit voltage of 1.41 V. Based on the device with effective area of 1 cm2 and 60.075 cm2, the record power conversion efficiency of 5.41% and 1.14% is obtained. The device also displays excellent stability with driving water electrolysis. The high‐valence Eu3+ was applied in carbon‐based printable mesoscopic inorganic CsPbBr3 perovskite solar cells (PSCs) for the first time. The high open‐circuit voltage and stability of the device demonstrate that the CsPbBr3 PSC is a promising device to drive the water electrolysis device.