Interface analysis in CdTe/CdS solar cells

We present results of chemical composition analysis across CdTe/CdS interfaces using depth profiling in Auger electron spectroscopy (AES) and secondary ion mass spectrometry (SIMS). The analysis of these buried interfaces is typically challenging due to significant interface broadening due to CdTe initial roughness and developing roughness during depth profiling. We have developed two alternative methods for sample preparation, namely chemical etching and mechanical polishing, and we will present S conc. profiles obtained using both methods in samples grown with variable CdTe temperature. AES depth profiling near bottom of CdTe solar cells showed widening of S conc. profiles for the hottest CdTe as compared to the coldest CdTe. In addition, the peak S conc. decreases from the coldest to the hottest sample, suggesting that S out-diffusion from CdS is also temperature dependent. Finally we employ focused ion beam cross-sectioning and scanning electron microscopy to measure layer thicknesses, evaluate the success of the sample preparation methods, and to discuss the effects of interface roughness on S conc. profiles and Te-S interdiffusion.