Characterization of sputtered CdSe thin films as the window layer for CdTe solar cells

CdSe film is noteworthy for its application in CdTe solar cells. In this paper, the crystal structure, surface profile and optical properties of CdSe films deposited at 25 degrees C, 200 degrees C, 250 degrees C, 300 degrees C and 350 degrees C by magnetron sputtering are investigated by XRD, SEM, AFM and an UV-VIS spectrometer. XRD patterns show that CdSe films deposited at 200 degrees C and 250 degrees C have cubic structure, which hasn't been reported so far for sputtered CdSe films. CdSe films deposited at 300 degrees C and 350 degrees C are hexagonal. Then CdSe films with different substrate temperatures (25 degrees C, 200 degrees C, 250 degrees C and 300 degrees C) were used as the window layer for CdTe solar cells. CdSe/CdTe device with CdSe film deposited at 250 degrees C reaches the highest efficiency. Quantum efficiency (QE) was enhanced in the range of 300-510 nm and 830-900 nm for CdSe/CdTe device (CdSe film deposited at 250 degrees C) compared to CdS/CdTe device while in the range of 510-830 nm, QE of CdSe/CdTe device was lower than that of CdS/CdTe device indicating an inferior junction between CdSe and CdTe. The results also suggest that CdSe deposition temperature influences the film structure and further to the interfusion between CdSe and CdTe which has a significant effect on device performance.