Phase-transition-driven growth of compound semiconductor crystals from ordered metastable nanorods

In polycrystalline semiconductors, grain boundaries are often sites with prevalence for electron-hole recombination and various strategies have been followed to minimize grain boundary areas. Generally, large grains or epitaxial films can be obtained at high temperatures. However, high growth temperatures limit the choice of substrate materials and can prove elusive for semiconductors comprising volatile elements such as kesterite Cu2ZnSnS4. Here we show that this limitation can be overcome by a transition of a matrix of densely packed metastable nanorods into large stable grains. Real-time analysis reveals that the grain growth is driven by a direct, isocompositional solid-state phase transition. Following this route, semiconductor films with a large-grained microstructure can be achieved within a few seconds at relatively low temperatures. Grain size as well as electrical and optical properties of the resulting films can be controlled via the heating rate. This synthesis route opens new possibilities for the fabrication of semiconductor crystals for photoelectric devices with tailored microstructures. Grain boundaries often play a detrimental role in polycrystalline devices such as solar cells, and larger grain sizes are preferred. Here, Mainz and colleagues show that a solid-state phase transition can transform metastable Cu2ZnSnS4compound semiconductor nanorods into large stable grains.