Photovoltaic Performance Enhancement of All‐Inorganic CsPbBr3 Perovskite Solar Cells Using In2S3 as Electron Transport Layer via Facile Reflux‐Condensation Process

All‐inorganic perovskite solar cells (PSCs) have attracted tremendous attention over the past few years owing to their outstanding thermal and moiture stability. Electron transport layers (ETLs) in PSCs play a prominent role of electron extraction and transportation as well as hole blocking for a high power conversion efficiency (PCE). Indium sulfide (In2S3) films have been introduced as a promising ETL of PSCs recently due to their high carrier mobility, appropriate band gap, and controllable electrical characteristics. Herein, a facile wet chemistry method is proposed to prepare In2S3 films for the ETLs of all‐inorganic CsPbBr3 PSCs with an architecture of fluorine‐doped tin oxide/In2S3/CsPbBr3/carbon. The resultant compact In2S3 films show a certain visible light absorption with a bandgap of 2.51 eV. With the optimal 3000 rpm speed of In2S3 spin‐coating, the best‐performing In2S3 based device presents a higher champion PCE of 5.83% with open circuit voltage of 1.34 V, a short circuit current density of 6.74 mA cm−2 and a fill factor of 0.65. The better performance of devices based on In2S3 ETLs is attributed to their more suitable energy level matching with less open circuit voltage loss, better light harvesting, and electron extraction capability enhancement. A reflux condensation sol spin‐coating technique is proposed to prepare indium sulfide (In2S3) films for the electron transport layer (ETL) of CsPbBr3 perovskite solar cells. The In2S3 films are compact, smooth and pinhole‐free with a facile and controllable process. The best‐performing device based on In2S3 ETL obtains the highest power conversion efficiency of 5.83%.