A facile two-step-heating route to synthesize hierarchical metastable wurtzite Cu2ZnSnS4 microcrystals under the open-air condition

•Metastable wurtzite CZTS were synthesized under the open air condition.•The hierarchical structure of wurtzite CZTS was reported for the first time.•The synthesis process was facile and environment-friendly.

With a novel solvent, the mixture of triethanolamine (TETA) and ethylene glycol (EG), hierarchical metastable wurtzite Cu2ZnSnS4 (CZTS) microcrystals were successfully synthesized by a facile two-step heat-up route under the open-air condition. XRD, SEM, EDS, HRTEM, Raman and UV–vis spectrum were employed to characterize the as-synthesized samples. The results indicated that the obtained product was hexagonal wurtzite CZTS microcrystals with single phase and stoichiometric composition, furthermore, consisting of microflakes (250–600 nm in diameter) with nanorods (10–20 nm wide, 50–150 nm long) on their surfaces. Ultraviolet-visible (UV–vis) spectrophotometry measurement shows that the band-gap energy of the as-synthesized CZTS was 1.45 eV, matching well with the optimal direct band gap of ~1.5 eV.