Phase selective synthesis of metastable orthorhombic Cu2ZnSnS4

Cu2ZnSnS4 (CZTS) is acknowledged as an alternative to traditional p-type semiconductors. Traditionally obtained CZTS, however, is mostly kesterite or stannite phase, which features a tetragonal crystal cell. Herein, novel orthorhombic CZTS has been synthesized via an ethylenediamine-assisted hydrothermal method. Ethylenediamine plays an important part in the construction of the orthorhombic phase. Kesterite CZTS was also obtained in an ultrapure water system without ethylenediamine. The structure was confirmed by XRD, XPS and HRTEM. The band gap of the orthorhombic CZTS is about 1.45 eV, which approaches the optimum value for solar photoelectric conversion. What's more, we found that this orthorhombic CZTS is metastable. After annealing at 500 degrees C, a phase transformation from the orthorhombic structure to the tetragonal kesterite structure was achieved. The photoelectric response was also characterised, which demonstrated its potential for application in photovoltaic devices.