A robust approach to fabricate CZTSSe absorber layer for solar cells via a self-selenizations process conducted by concentrated selenium solution

Abstract

It was reported that most of copper zinc tin sulfoselenide (CZTSSe) had been prepared via the conventional rapid thermal selenization of copper zinc tin sulfide (CZTS) using external selenium source. This approach often shows low utilization efficiency and high waste of selenium source, which will hamper the development of CZTSSe in solar cells. In this work, CZTSSe thin films with high crystallinity were designed by self-selenizing CZTS nanocrystalline thin films via direct rapid thermal processes (RTP) conducted by superficial selenium solution. The transformation processes of selenizing CZTS thin films into CZTSSe were systematically investigated by field emission scanning electron microscope, x-ray diffraction, and confocal micro-Raman spectroscopy. The results showed that CZTS nanocrystals only partially transformed into CZTSSe nanocrystals during RTP in selenium solution, while they can further be self-selenized by the residual elemental Se in a post-RTP process. More interesting, the energy dispersive x-ray spectroscopy indicated that selenium elements can be highly dispersed into CZTSSe thin films. Furthermore, the assembled solar cell using the obtained CZTSSe thin films can output power conversion efficiency of 1.96% for a total area of 0.5 cm2 (with an active area of 0.456 cm2) under standard AM 1.5 illumination. This research would give a new insight for preparation of high quality CZTSSe thin films.