Characterization and Modeling of ZnO/CdS/CdTe Heterojunction Thin Film Solar Cells

At present, amorphous silicon solar cells have the largest market share in the world, with less than a fraction of one percent for CuInGaSe2 and about a few percent for CdTe cells. The benefit of using CdTe is primarily due to its direct bandgap material with high absorption (in relationship with silicon) and the ease of device processing, which can be deposited on glass in thin film typically a few micrometers and at low temperatures. This study intends to discuss the characterization and modeling of CdS/CdTe heterojunction thin-film solar cells for high-efficiency performance. Device simulation is employed to analyze the current-voltage efficiency performance of CdTe/CdS photovoltaic solar cells. Key limiting factors, including the back-contact Schottky barrier, its relationship to doping density, and layer thickness, are investigated. Additionally, the effects of surface recombination velocity at the back-contact interface and the inclusion of an extended CdTe layer are evaluated. The experimental base CdS/CdTe device used in this study demonstrates an efficiency of 16–17%. Through simulation analysis under the AM1.5 solar spectrum, optimization strategies for the experimental device are explored. The results indicate that enhanced efficiency can be achieved by incorporating and optimizing an extended CdTe electron reflector layer at the back of the Schottky contact. Specifically, an extended electron reflector region with a barrier height of 0.1 eV, a doping density of 7x1018 cm-3, and an optimal thickness of 100 nm yields a maximum cell efficiency of 19.83%, outperforming the experimental data.