Study of sulphidation of Cu–In nanoparticle precursor films with an air-stable process

The large-grained and high crystalline CuInS₂ films were prepared based on a metal-nanoparticle ink method, assisted by an air heat treatment (air-stable) process. Cu–In nanoparticles were firstly prepared in polyol by a simple chemical reducing method. And then, Cu–In nanoparticles, polyvinyl pyrrolidone, and alcohol were used to compose inks, which were drop-coated onto substrates to form precursor films. Moreover, Cu–In nanoparticle precursor films were sulphurised to form CuInS₂ films in H₂S atmosphere at different temperatures. An additional air-heat treatment (air-stable process) was also introduced before sulphurising to improve quality of the prepared CuInS₂ films. At first, grain sizes of prepared CuInS₂ were very small. And then, grain sizes of prepared CuInS₂ grew largely by sulphurising Cu–In nanoparticle precursor films with an air-stable process. Finally, XRD, Raman measurement, transmittance, absorbance spectra and Hall Effect were adopted to identify the films. The results show that the air-stable process is feasible to improve the CuInS₂ films prepared by solution-based deposition techniques.