A review on integration of Zn based buffer layers in II-generation solar cells for enhanced efficiency

Photon-driven technologies encompass the utility of carefully engineered materials for myriad applications. Over the past decade, thin films of II–VI chalcogenide materials have emerged as versatile candidates for the efficient construction of photovoltaic devices. The buffer layer which serves as a lattice fixer in solar cells plays a role in determining the photon-driven processes between the absorber and the window layers, significantly affecting the performance of the working device. However, mostly used buffer layer, CdS is highly toxic. Recently, there is quest to replace the highly toxic cadmium sulfide (CdS) buffer layers with Zn-based materials to obtain high-efficiency solar cells. Among the II–VI compounds, zinc sulfide (ZnS) and zinc selenide (ZnSe) present promising futuristic scope for research in the photovoltaics field and are recognized as alternatives to the widely used toxic CdS buffer layer. Although significant research has been devoted in this direction, a comprehensive review capturing the latest advancements in photon-driven technologies pertaining to Zn based buffer layers in photovoltaics, has not yet been conducted. In light of these observations, we present a review focusing on the recent progress in the incorporation of Zn based buffer layers into different solar cells constituting CdTe, CIGS, and CZTS. The light matter interactions that depend on the thickness, and the band alignment of the buffer layer with the absorber is discussed in detail.