Transmission electron microscopy analysis for the process of crystallization of Cu₂ZnSnS₄ film from sputtered Zn/CuSn precursor.
The mechanism of crystallization of Cu₂ZnSnS₄ (CZTS) made by the sulfurization of a sputtered Zn/CuSn stack was studied by transmission electron microscopy. At 250 °C, the Zn buried at the bottom of the metallic stack was found to be driven to the upper layer by alloying with Cu and reacting with S to form ZnS. At 500 °C, CZTS was found to be formed and elemental Sn was observed in the vicinity of the back contact region, while large quantities of Cu₂S and ZnS were segregated at the film surface. At 575 °C, Cu₂SnS₃ was found, while all the elemental Sn had vanished. Upon extending the duration of the annealing to 10 min, at 575 °C, all the secondary phases except ZnS were consumed and the CZTS formation was completed, while around 200 nm of MoS₂ was formed between the CZTS layer and Mo back contact. The finished solar cell exhibits an efficiency of 2.66%, an open-circuit voltage of 666.9 mV and a short-circuit current density of 9.14 mA cm⁻². The solar cell performance is possibly limited by the thick MoS₂ layer and the large density of voids in the back contact region due to the Sn loss at high sulfurization temperatures.
School of Photovoltaic and Renewable Energy Engineering, University of New South Wales, Sydney, NSW A-2052, Australia.
Wei
W
Li
Jian
J
Chen
Chang
C
Yan
Fangyang
F
Liu
Xiaojing
X
Hao