Abstract:
Cu2ZnSnS4 is one of the most promising quaternary absorber materials for thin-film solar cells, since it is a strong candidate low-cost material with the optimal single-junction band gap 1.5 eV and a high adsorption coefficient. Although the existence of such compound could be almost 50 years, due to the complicity of quaternary compound, the properties are not well determined, which are crucial for the application of the solar absorber.
In this talk, I will present our understanding on the structure evolution from binary, to ternary and to quaternary compound by sequential cation cross-substitution in zinc-blende chalcogenide semiconductors. We found that the low energy crystal structure obeys the octet rule and predicted the ground state structure of CZTS to be kesterite, which is experimentally confirmed very recently. Examination of the thermodynamic stability of this quaternary compound reveals that the stable chemical potential region for the formation of stoichiometric compound is small. Under these conditions, the dominant defect in CZTS will be p-type CuZn antisite, which has an acceptor level deeper than the Cu vacancy. We propose that to maximize the solar cell performance, growth of Cu2ZnSnS4 under Cu-poor/Zn-rich conditions will be optimal, if the precipitation of ZnS can be avoided by kinetic barriers.
Coffee and tea will be served 20 minutes prior to the seminar.