Investigation of sulphur diffusion at the CdS/CdTe interface of thin-film solar cells

Diffusion of atoms across the CdS/CdTe interface during post‐deposition annealing is thought to have an important effect on the performance of CdS/CdTe‐based solar cells. Thin‐film solar cell samples were annealed at 400°C for three different times. The samples were etched sequentially in a bromine/methanol solution and then examined with Auger depth profiling and X‐ray diffraction. Profiling showed the as‐deposited samples to have little or no interfacial mixing, but annealing even for a short time caused diffusion of sulphur into the CdTe material. As the annealing times lengthened, the concentration of sulphur in the CdTe increased. X‐ray diffraction measurements indicated that the CdS layer rapidly crystallized into its hexagonal Greenockite modification, but with lattice parameters increased by 0.8%. This changed little with annealing time. The CdTe near the interface appeared to have a modified but well‐defined cubic structure with respect to reference CdTe, as indicated by splitting of the diffraction peaks, denoting the growth of a CdTexSy interfacial layer. This layer increased in thickness with annealing time and most probably has a stoichiometry within the range CdTeS0.04–CdTe0.88S0.12. Copyright © 2002 John Wiley & Sons, Ltd.