Analysis of CdSe as an alternative buffer layer for Sb2Se3 solar cells

In this work, for the first time, CdSe is applied as a buffer layer on thermally evaporated Sb2Se3-based solar cells on superstrate configuration. The influence of this buffer layer on the growth of Sb2Se3 and the performance of the finished devices have been analyzed and compared with the typical CdS/Sb2Se3 junction. Selenium vacancies in Sb2Se3 thin film act as recombination centres, for this reason applying an excessive amount of Se is beneficial to the performance of the devices. In the case of the CdS/Sb2Se3 structure, the high concentration gradient enhances the selenium diffusion into the CdS and the sulphur diffusion into the Sb2Se3 resulting in an increased number of defects. The replacement of CdS with CdSe would allow us to avoid this detrimental effect. In this work, we show that CdSe improves the external quantum efficiency in the entire light spectrum, increasing the average current density of the devices up to 2 mA/cm2 in comparison to CdS/Sb2Se3. Also, the fill factor improves while the Voc slightly decreases due to the narrower band gap. Moreover, CdSe/Sb2Se3 samples demonstrate excellent stability under accelerated stability tests.