The nature of electrostatic potential fluctuations in Cu2ZnSnS4 and their role on photovoltaic device performance

Aberration corrected STEM EELS is used to investigate point defects in Cu2ZnSnS4 (CZTS). Nano-scale clusters of Zn-Cu anti-site donors are observed with the donor concentration being sufficiently high to degenerately dope the semiconductor. Uncompensated donors and acceptors result in electrostatic potential fluctuations within the material. The effect of these potential fluctuations on the photovoltaic device properties is discussed.