Boosting the efficiency of carbon-based planar CsPbBr3 perovskite solar cells by a modified multistep spin-coating technique and interface engineering

All-inorganic CsPbBr 3 perovskite solar cells (PSCs) have attracted tremendous attentions in the photovoltaic field these days in view of their outstanding stability, especially thermal stability. However, the bromide-rich perovskite , such as CsPbBr 3 , always suffer from a low phase-purity and poor morphology synthesized by traditional two-step deposition route. Herein, we demonstrate a facile multistep spin-coating strategy to fabricate high-quality CsPbBr 3 films on the low-temperature processed compact TiO 2 ( c -TiO 2 ) electron transport layer (ETL) of the carbon-based PSCs. As-prepared films exhibit more homogeneous with higher CsPbBr 3 -phase purity and larger average grain sizes up to 1 µm, compared to those prepared through traditional two-step deposition process . The champion power conversion efficiency (PCE) of the planar CsPbBr 3 PSC is boosted from 7.05% to 8.12%, getting an increase by 15.2%, due to the increased crystallinity and light-harvesting ability as well as reduced trap states of the CsPbBr 3 film. To further enhance the device performance, a SnO 2 thin layer with much higher carrier mobility than TiO 2 is introduced to passivate the c -TiO 2 ETL. It is found that the SnO 2 layer can not only improve the surface morphology of the ETL, but also reduce the current shunting pathways in the c -TiO 2 . The TiO 2 /SnO 2 bilayered ETL possesses a superior electron extraction capability, beneficial to the charge transport and suppression of the interfacial trap-assisted recombination. The best-performing TiO 2 /SnO 2 -based CsPbBr 3 PSC delivers an excellent fill factor of 0.817 and a high PCE of 8.79%, which is the highest efficiency for planar CsPbBr 3 PSCs reported to date. More importantly, the unencapsulated all-inorganic PSCs show a promising humidity and thermal stability with no decline in efficiency when stored in ambient air at room temperature (25 °C) for over 1000 h and 60 °C for one month, respectively. Our work pave the ways for practical applications of cost-effective, highly efficient and stable all-inorganic PSCs.