ABSTRACT
Bismuth-based double perovskite Cs2AgBiBr6 shows promise as a photodetection material. However, its detection performance and application are limited by high-exciton binding energy and poor carrier mobility. In this study, we address these limitations by delicately designing a solution-based method for incorporating A-site Rubidium (Rb) substitution into Cs2AgBiBr6 double perovskite films. The introduction of Rb resulted in a significant decrease in trap defect density and an improvement in film quality. The trap-filled limit voltage (VTFL) of pure and Rb-doped CABB film is determined to be 1.71 V and 0.48 V, respectively. Subsequently, by introducing an ultrathin atomic-layer-deposited (ALD) TiO2 films, the fabricated CABB photodetectors exhibit significantly improved photoresponse performance. The response speed and -3dB bandwidth are boosted from â¼93 ms to â¼350 µs and broadened from 1.4 kHz to 17 kHz, respectively. Density Functional Theory (DFT) calculations indicate Rb-substitution shortens the bond length and weaken exciton binding energy. Furthermore, we demonstrate a wireless near ultraviolet (UV) light communication system using CABB photodetectors as light receivers. Our findings provide an efficient approach to utilize A-site cation substitution as a tuning parameter for photodetection in high-exciton binding energy perovskite materials, thereby extending the potential applications of other functional perovskites.
ABSTRACT
Low-temperature synthesis of high-quality, high-stability, wide-bandgap perovskite films by solution methods is still challenging. Herein, large-scale wide-bandgap Cs2AgBiCl6 (CABC) double perovskite films are synthesized by a vapor-phase anion-exchange strategy. By dedicatedly designing an ultrathin TiO2 modification layer between the substrate and double perovskites, high-quality heterojunctions with matched energy band alignment are formed, contributing to a remarkably enhanced ON/OFF ratio of 2.4 × 104 (86 times) and a responsivity of 16 mA W-1 (12 times). Additionally, the ultraviolet photodetectors (UV PDs) exhibit an excellent UV detection limit of 1.18 µW cm-2 (20 nW), a broad linear dynamic range of 146 dB, and a high specific detectivity of 2.06 × 1011 Jones, as well as long-term stability. Finally, we further demonstrate a weak UV imaging system using CABC UV PDs as imaging sensors. The system is capable of imaging weak UV signals as low as 2.94 µW cm-2 (50 nW). Our results provide a feasible approach for low-temperature fabrication of wide-bandgap perovskite UV PDs and explore the promising application for weak UV detection and imaging.
