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 (VOC) 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.