Solvent vapor annealing-assisted mesoporous PbBr2 frameworks for high-performance inorganic CsPbBr3 perovskite solar cells

In recent years, CsPbBr3 perovskite solar cells (PSCs) have attracted the attention of a large number of researchers due to their excellent temperature and humidity stability. And in the current studies, due to the lack of suitable solvents to dissolve PbBr2 and CsBr at the same time, most studies have used sequential solution-processing techniques (SSPTs) to prepare CsPbBr3 films. However, in the process of the sequential deposition of PbBr2 and CsBr, the uneven reaction could lead to the generation of impure phase (e.g. CsPb2Br5 and Cs4PbBr6), which would deteriorate the photoelectric performance of the device. Here, a solvent-vapor annealing (SA) method has been proposed for fabricating mesoporous PbBr2 films by exposing the PbBr2 films in N,N-Dimethylformamide (DMF) vapor environment. The porous PbBr2 frameworks could facilitate the reaction with CsBr to fully convert into inorganic perovskite CsPbBr3. A series of characterization results show that a compact, uniform and high-quality CsPbBr3 film with large grains was obtained, where the porosity of PbBr2 scaffold could be tuned by the volume of DMF. Consequently, the devices based on optimized PbBr2 films treated by SA method achieved a champion power convention efficiency (PCE) of 9.60%, an open-circuit voltage (VOC) of 1.54 V, a short-circuit current density (JSC) of 7.57 mA cm−2 and a fill factor (FF) of 82.37%, compared with the devices treated by conventional thermal annealing (TA) method achieved a PCE of 8.42%, a VOC of 1.49 V, JSC of 7.31 mA cm−2 and FF of 77.30%. Furthermore, the SA treated devices exhibit more durable stability than TA treated devices, and the SA treated devices still retain 94.28% of its original PCE without any encapsulation in the ambient atmosphere after 30 days.