Contact angle measurements: an empirical diagnostic method for evaluation of thin film solar cell absorbers (CuInS2)

An empirical diagnostic method for the evaluation of solar cell grade CuInS2 absorbers has been developed. The method involves the measurement of the contact angle between water and the CuInS2 absorber before fabrication of a solar cell. The contact angle is expected to depend upon local inhomogeneity, chemical composition and surface morphology of the CuInS2 absorber. The variation of these factors on the surface is supported with scanning electron micrographs, chemical analyses, laser scanning photocurrent mapping of various CuInS2 absorbers and measurements of the solar cell performance. The contact angle has been found to be different at different places on the CuInS2 surface. Empirically, it was found that for high conversion efficiency solar cells (>8–10.5%), the contact angle on CuInS2 absorbers ranges between 53° and 63°. For low conversion efficiency solar cells (<6%), it is between 48° and 50°. Therefore, it is seen that contact angle measurements on CuInS2 absorbers can be used to assess the quality of CuInS2 absorbers prior to solar cell fabrication.