Investigation of the effect of UV radiation on n-CdS/p-Cu2S solar cells produced with different techniques

Abstract

In this study, n-CdS/p-Cu₂S heterojunctions were fabricated by the chemical deposition of CuCl onto CdS films produced using thermal and cryogenic techniques. Initially, the structural, morphological, and optical properties of CdS films grown on glass/indium tin oxide (ITO) substrates at room temperature (300 K) and at a cryogenic temperature (200 K) were examined. Field emission scanning electron microscopy (FESEM) analyses revealed that the CdS film produced at 200 K exhibited a more uniform and compact surface morphology compared to the film grown at 300 K. X-ray diffraction (XRD) measurements showed that both films crystallised in the hexagonal (002) preferred orientation without any additional phase reflections. Cross-sectional scanning electron microscopy (SEM) images indicated film thicknesses of approximately 2.5-3 µm. Optical transmittance measurements demonstrated that the CdS film grown at 200 K had higher transparency. The photocurrent responses of the resulting CdS/Cu₂S solar cells were evaluated as a function of wavelength, and the device fabricated at 200 K displayed a broader spectral sensitivity. Photovoltaic parameters obtained from current-voltage (I-V) measurements were analysed to compare the performance of the heterojunctions. In the second stage, the photodevices were exposed to 360 nm Ultraviolet (UV) radiation for 1, 3, and 5 hours to investigate UV-induced effects. The results showed that the solar cell containing the CdS layer grown at 200 K exhibited greater resistance to UV degradation. According to capacitance-voltage (C-V) measurements, the charge carrier density (N_d) of the photodevice produced at 200 K remained nearly unchanged after UV exposure, which was attributed to the reduced density of acceptor-type defects formed at lower substrate temperatures.