Phase-Selective Synthesis of Cu2ZnSnS4 Nanocrystals through Cation Exchange for Photovoltaic Devices

Cu2ZnSnS4 (CZTS) nanocrystals with two typical structures, i.e., zinc blende (ZB)-derived and wurtzite (WZ) crystal frameworks, have been selectively synthesized via a solution-based route. Initially, Cu2SnS3 (CTS) nanoparticles with two different phases, i.e., zinc blende- and wurtzite-derived, can be prepared with different S sources and temperatures. Afterward, addition of the Zn precursor to the CTS matrix results in the substitutions of Cu and Sn cations, yielding CZTS with desirable phases. This method can be extended to the synthesis of other similar quaternary chalcogenide nanocrystals. The cation exchange method described here provides a convenient approach for fine-tuning the nanocrystal's cation ratio, which enables us to optimize the solar absorber layer compositions and get a power conversion efficiency of 2.89% in copper-poor and zinc-rich devices. The capability to synthetically access stable phases with controllable morphologies and compositions demonstrates that the developed cation exchange method is powerful as a manufacturing technique for photovoltaic devices.