Studying the effect of Sn doping on the optoelectronic properties of PbI${}_2$ nanosheets/Si heterojunction photodetector prepared by chemical bath deposition

This study focuses on the preparation of PbI${}_2$ and PbI${}_2$:Sn thin films using inexpensive chemical bath deposition (CBD) method. The structural, optical, and electrical properties of the PbI${}_2$ film before and after doping with Sn dopant were studied. X-ray diffraction (XRD) confirmed that the grown PbI${}_2$ and Sn-doped PbI${}_2$ films are crystalline, exhibiting a hexagonal phase, while peaks corresponding to the SnI${}_4$ phase were detected. The energy-dispersive X-ray (EDX) analysis and elemental mapping results reveal the presence of the Sn dopant. Scanning electron microscopy (SEM) studies confirm that the prepared PbI${}_2$ and Sn-doped PbI${}_2$ films have a hexagonal structure. The energy gap of the deposited PbI${}_2$ film decreases from 2.7 to 2.5 eV after doping with Sn. The room-temperature current-voltage characteristics of PbI${}_2$/Si and PbI${}_2$:Sn/Si heterojunction photodetectors were measured under dark and illumination conditions. The spectral responsivity, specific detectivity, and external quantum efficiency of the photodetectors were determined before and after doping. The peak response of the PbI${}_2$/Si photodetector was found at 550 nm with a responsivity of 0.08 A/W, while the peak response of the PbI${}_2$:Sn/Si photodetector was located at 500 nm with a responsivity of 0.29 A/W. The external quantum efficiency of PbI${}_2$/Si and PbI${}_2$:Sn/Si was 18 and 82%, respectively. The specific detectivity of the photodetector increases from 3.1 × 10${}^{11}$ to 9.2 × 10${}^{11}$ after doping. The energy band diagram of PbI${}_2$:Sn/Si under illumination is presented.