Preparation of a CuInS2 Nanoparticle Ink and Application in a Selenization‐Free, Solution‐Processed Superstrate Solar Cell

Abstract

AbstractWe report a study on chalcopyrite solar cells fabricated by low‐cost, nonvacuum, and selenization‐free methods. Superstrate‐type CuInS2 (CIS) thin‐film solar cells were prepared by sequential ink deposition. The CIS film was formed from a stable low‐carbon ink, which was synthesized at low temperature (<120 °C). The CIS nanoparticle ink was prepared with n‐butylamine and acetic acid as the solvent and stabilizer, respectively. The viscous and stable ink that formed through the dispersion of the final nanoparticles in N,N‐dimethylformamide (DMF) could be deposited readily onto the substrate. The major features of the obtained ink are the small amount of impurity phases and negligible carbon residue (ca. 2.8 %). The obtained ink was used for the fabrication of superstrate solar‐cell devices with a glass/FTO/TiO2/In2S3/CIS/carbon (FTO = fluorine‐doped tin oxide) structure. The performance of the solar cells was improved by optimizing different synthetic and geometric parameters, including the sulfur source, reaction time, reaction temperature, buffer‐layer thickness and second annealing temperature. The best cells were obtained by using inks with thiourea as the sulfur source, and a high current density of 21 mA/cm2 and 5.2 % efficiency were obtained. This current density is the highest among those reported for solution‐based superstrate CIS solar cells and is comparable to those of solar cells fabricated with a selenization step at high temperature. The ink is stable, and the efficiency of the device fabricated with ink aged for 100 d is ca. 12 % less than that of the device fabricated with fresh ink.