Effect of CdCl2 annealing treatment on interdiffusion and reaction at the CdS/CdTe interface

A structure of Glass/FTO/CdS/CdTe/CdS based on the CdTe solar cell (Glass/FTO/CdS/CdTe) was adopted to study the effect of CdCl2 annealing treatment on the interdiffusion and the related reaction at the CdS/CdTe interface. Investigations show that surface morphology changs dramatically under different annealing treatment temperatures. The crystal size of CdS increases from 20 nm to 70 nm between 300～350 ℃. This temperature range is consistent with that of the CdS sphalerite to wurtzite phase transformation. CdS/CdTe interdiffusion happens at around 350 ℃, and CdS0.85Te0.15 with hexagonal-wurtzite structure is detected at 550 ℃. The CdS is quickly consumed up through interdiffusion with CdTe and forming CdSxTe1-x alloy. CdTeO3 begins to form at 450℃. Raman scattering shows that the intensity of CdS 1LO peak decreases from 350 ℃ and shifts to lower frequency, which reveals the formation of CdSxTe1-x. The XPS spectrum of samples confirms the formation of CdSxTe1-x and CdTeO3. CdCl2 protects CdS/CdTe from oxidation and promotes interdiffusion at the interface and formation of CdSxTe1-x during air annealing.