Enhanced device performance of Cs2AgBiBr6 double perovskite photodetector by SnO2/ZnO double electron transport layer

In this study, we report the enhancement of device performance in a lead-free perovskite Cs2AgBiBr6-based deep blue photodetector by using a SnO2/ZnO double electron transport layer (ETL). The SnO2 layer was inserted to minimize the energy loss at the interface between the ZnO ETL and perovskite absorber layer by preparation of a smooth perovskite film. The hydrophilic SnO2 layer coating on the hydrophobic ZnO nanorods provides a uniform and high-quality perovskite layer without pinholes. Reduced contact angle measurement confirmed that the surface property changes towards hydrophilicity after insertion of a SnO2/ZnO double ETL compared with bare ZnO nanorods. Moreover, the introduction of the SnO2 layer leads to better carrier transportation and extraction by matching the energy level between the perovskite and ZnO ETL. The pinhole-free perovskite film and a well-matched energy level are responsible for the Cs2AgBiBr6-based visible photodetector with a SnO2/ZnO double ETL demonstrating simultaneous improvement of responsivity and specific detectivity by 12.7 times and 16.5 times, respectively, compared with those of the ZnO single ETL. From our results, we can suggest a guideline for an interface engineering strategy to improve perovskite optoelectronic device performance.