CdS/CdTe thin-film solar cells are one of the cost-effective and reliable photovoltaic devices, with reported power conversion efficiencies of over 22 %. The CdTe/CdS solar cell is composed of a transparent conductive layer as a front contact, n-CdS window layer, p-CdTe absorber layer and a back contact on top of CdTe layer. The conventional CdS/CdTe solar cells have Cu back contact.  Although Cu doped CdTe hole-transporter significantly enhances the efficiecncy of CdS/CdTe solar cells by the forming a p⁺ rich hole-transporting layer, this process lead to low photovoltage and electrical instability due to copper diffusion to the CdS/CdTe interface.

This study focuses on fabricating stable and efficient CdS/CdTe thin-film solar cells with thermally evaporated copper halides, CuX (X = Cl, Br and I) as hole-transporting material (HTM) by replacing Cu back contact to avoid Cu diffusion. For the device fabrication, the n-CdS window layer was fabricated by the chemical bath deposition (CBD) method on a cleaned FTO substrate, and then the p-CdTe absorber layer was deposited by closed space sublimation (CSS) on top of the CdS layer. In order to study the effect of a CuX hole-transport layer on the photovoltaic performance of CdTe solar cells, CuX films were deposited on the CdTe films by thermal evaporation. Au layer of thickness 80 nm was then thermally evaporated on CuX layer as a back electrode. The fabricated device was annealed at 200 °C for 10 min under N₂ environment. Properties of CuX layer were characterised by XRD, SEM, AFM, UV-Visible spectroscopy and XPS. Finally, CdS/CdTe devices with CuX film were fabricated and photovoltaic performances were successfully examined under illuminations of 100 mW/cm² (1 sun) with an Air Mass of (AM) of 1.5 filter.  The experimental results show that the fabricated CdS/CdTe thin-film solar cells with CuX hole-transporters have better stability than CdS/CdTe thin-film solar cells with Cu/Au back contacts.