ZnSe/ITO and ZnSe/SnO₂ Thin Films as Window Layer for Sb₂Se₃ Heterojunction Solar Cells by CSS Method

ZnSe, an A₂B₆ semiconductor compound with a wide band-gap (about 2.7 eV) and cubic zinc blend structure, it seems to be very promising window for Sb₂Se₃ heterojunction solar cells. In this paper, we study the effect of substrate temperature on the physical properties of ZnSe films deposited on SnO₂/glass and ITO/glass substrates by the closed-space sublimation method (CSS).Thin films were characterized using SEM, energy dispersive analysis (EDX), X-ray diffractogram (XRD), and UV–Vis spectra. The XRD studies of ZnSe thin films deposited on both, SnO₂/glass and ITO/glass substrates, show that the structure is zincblende, with preferred orientation along the (111) plane and nanograins sizes depend on the substrate temperature. Also, the lattice parameters showed a dependence on the substrate temperature, for example, with increasing substrate temperature from 500 K to 600 K, the lattice parameter of ZnSe/SnO₂/glass changed from 5.6707 Å to 5.6571 Å, respectively. SEM images in both cases, indicate uniform deposition without pin holes and EDS patterns confirm the deposition of the as-grown Zn-deficient thin films. The average transmittance in the domain from 600 nm to 1200 nm of the spectra was ranged between 85% and 90% for all studied samples. The measured reflectance spectra have been transformed in the absorption spectra, and by applying the Kubelka−Munk function, the values of the band-gap width were estimated. These values slightly change but are in good agreement with those reported for bulk ZnSe samples. The properties of as-deposited ZnSe thin film on different nature substrates were tailored by chemical activation and thermal annealing. The effects of chemical activation and thermal annealing in different atmosphere, on the structural, optical and electrical properties of the films will also be discussed in this paper.