Tri‐Step Water‐Assisted Strategy for Suppressing Cs 4 PbBr 6 Phase in Printable Carbon‐Based CsPbBr 3 Solar Cells to Achieve High Stability

Often deemed the "natural nemesis" of perovskites, water molecules have been largely circumvented by the majority of researchers in the field of perovskite solar cells. This has resulted in significant hurdles in investigating the beneficial impacts of water molecules on perovskite crystallization. Herein, it is found that by utilizing ethanol with minimal water content and subjecting all-inorganic perovskite to three distinct annealing temperatures within the same solvent, the residual CsBr can be effectively removed, and the formation of the Cs₄PbBr₆ phase can be curtailed. By selecting an optimal water content, substantial improvements are observed in the crystalline quality of CsPbBr₃, the perovskite/carbon interface, and the mesoporous filling effect. The Urbach energy (E_u) is reduced from 38.96 to 35.59 meV, and the defect density decreased from 4.16 × 10¹⁴ to 3.39 × 10¹⁴ cm^-3. As a result, the power conversion efficiency (PCE) improved from 7.55% in the control group to 9.37%. Under severe environmental conditions with a temperature (T) of 85 °C and a relative humidity (RH) of 40%, tracking tests over 1200 h retained 89.3% of the initial PCE. This research signifies a breakthrough in the fabrication of highly stable and efficient all-inorganic printable mesoscopic perovskite solar cells.