Fig. 1. Schematic of the MAPbBr₃/MAPbCl₃ heterojunction wafer preparation process (color online)

Fig. 2. SEM surface morphology images of MAPbBr₃ wafers (a) and MAPbCl₃ wafers (b), (c) SEM surface morphology images and (d) elemental mapping images of MAPbBr₃/MAPbCl₃ heterojunction wafers, (e) cross-sectional SEM and (f) elemental mapping image of MAPbBr₃/MAPbCl₃ heterojunction wafers, (g) XRD patterns of MAPbBr₃, MAPbCl₃ and MAPbBr₃/MAPbCl₃ heterojunction wafers

Fig. 3. UV-vis absorption spectra of MAPbCl₃ wafers (a), MAPbBr₃ wafers (b), and MAPbCl₃/MAPbBr₃ heterojunction wafers (c), and response spectra of MAPbCl₃/MAPbBr₃ heterojunction wafers (d)

Fig. 4. I-V curves of MAPbCl₃, MAPbBr₃, and MAPbCl₃/MAPbBr₃ heterojunction devices under dark (a) and light (b) conditions in the bias range of -20 to 20 V, UPS spectra of MAPbBr₃ and MAPbCl₃ (c), energy band structure diagram of MAPbCl₃/MAPbBr₃ heterojunction device (d), energy band diagrams of MAPbCl₃ and MAPbBr₃ (e), energy band diagrams of MAPbCl₃/MAPbBr₃ heterojunction under dark (f) and light (g) condition (color online)

Fig. 5. (a) On/off photocurrent response of MAPbBr₃/MAPbCl₃ heterojunction wafer detector to X-ray at different dose rates under 0 V bias, (b) Sensitivity curve of heterojunction detector at 0 V bias, (c) Signal-to-noise ratio (SNR) curve of heterojunction wafer devices, (d) Stability of heterojunction detector under continuous X-ray irradiation at high dose rates

Fig. 6. X-ray response at different doses (a), and sensitivity curves at different dose rates (b) of MAPbCl₃ wafers, MAPbBr₃ wafers, and MAPbBr₃/MAPbCl₃ heterojunction X-ray detectors under 10 V bias