A novel low-temperature growth of uniform CuInS2 thin films and their application in selenization/sulfurization-free CuInS2 solar cells

In terms of manufacturability, there is a high tendency to deposit light-absorbing CuInS2 films by solution processing methods like ink-based depositions. In particular, for nanoparticle inks, the synthesis of highly dispersed and stable inks, with uniformity in the deposition process, is a serious challenge. Here, we demonstrate a novel two-step low-temperature CuInS2 film deposition method in which the In2S3 is deposited first. It then partially is converted into CuInS2 through the infiltration of Cu+ ions in the In2S3 layer in a dip-coating process. The resulting films are highly uniform, with diffraction peaks indicating the formation of pure CuInS2 phase. The proper stoichiometry of CuInS2 layers is confirmed by the optical absorption spectrum, energy?dispersive x-ray spectroscopy, and X-ray photoelectron spectroscopy analysis. Our Cd-free devices are structured by FTO/TiO2/In2S3/CIS/carbon, in which the residual In2S3 film acts as a buffer layer. The results demonstrate that the planar superstrate CuInS2 solar cell with the optimized absorbing layer composition has a power conversion efficiency of 2.11 %, which is the highest reported efficiency for a low-temperature solution-based selenization/sulfurization-free CuInS2 device structures prepared by ion-exchange method.

Automated summary

A novel two-step low-temperature CuInS2 film deposition method is demonstrated in this study, which involves depositing In2S3 first and then partially converting it to CuInS2 through the infiltration of Cu+ ions. The resulting films are uniform and show diffraction peaks indicating the formation of pure CuInS2 phase. The proper stoichiometry of CuInS2 layers is confirmed by various analyses, and the power conversion efficiency of the CuInS2 solar cell reaches 2.11%, the highest reported efficiency for this type of device structure.