Intermixing and Diffusion Impact on CdS/CdTe/p⁺ Regions (Te or ZnTe)/Cu/Au Solar Cell Interphases

The polycrystalline CdS/CdTe thin film solar cell is one of the most important photovoltaic devices for cost-effective generation of solar electricity for terrestrial applications. A typical superstrate structure of CdTe solar cell has been studied through current-voltage (J-V) and secondary ion mass spectroscopy (SIMS) measurements. A close correlation between quality of interphases and its photovoltaic efficiency was determined. It was found an improvement of open circuit voltage (V_OC) and efficiency associated to CdS and CdTe thermal treatments, and a reduction of diffusion of S and Cd into CdTe and CdS respectively. An efficiency of 12% has been reached on solar cells with a Te and ZnTe interlayer as part of the back contact. Low diffusion of Cu along absorbent material was observed when Te and ZnTe was used creating a stable back contact along the time. Diffusion and intermixing at each junction SnO₂:F/CdS, CdS/CdTe and CdTe/Te or ZnTe/Cu/Au was found, establishing limit values of element diffusion along CdTe solar cells.

Keywords:
CdTe; Solar cells; Depth profile; photovoltaic efficiency; Diffusion; Intermixing; p⁺ regions