Preparation and characterization of pulsed laser deposited CdS/CdSe bi-layer films for CdTe solar cell application

Abstract CdS/CdSe bi-layer film was prepared by pulsed laser deposition with different substrate temperatures as an improved window layer for CdTe solar cells. The total thickness of each CdS/CdSe bi-layer film was about 70 nm, which could contribute to comparatively high transmittance of photons and, therefore, improving the photocurrent. Substrate temperature influenced the properties of the CdS/CdSe bi-layer films and the study showed that the bi-layer film prepared at 400 °C achieved the best optical transmittance and crystallinity. The crystal structure and optical transmittance of CdS/CdSe/CdTe stack before and after CdCl 2 annealing treatment were investigated by utilizing X-ray diffraction and UV/Vis spectrophotometer, respectively. It showed that further CdCl 2 annealing treatment improved the inter-diffusion of Se into CdTe, facilitating the formation of a CdTe 1−x Se x alloy in the absorber layer. Comparing with CdTe, the alloy actually showed a smaller band gap which produced an obvious red shift of the absorption edge in long wavelength region. CdSe window layer was consumed by the inter-diffusion, while enhanced the short wavelength response in the range of 300–500 nm. The device based on CdS/CdSe window layer realized a J SC enhancement due to the improved collection within both short and long wavelength regions accompany with a V OC enhancement when compared to CdS/CdTe solar cell. The CdTe cell with CdS/CdSe bi-layer window deposited at 200 °C showed an efficiency of 13.47% with V OC of 791 mV and J SC of 27.40 mA/cm 2 .