Modification of absorber quality and Mo-back contact by a thin Bi intermediate layer for kesterite Cu2ZnSnS4 solar cells

In this work, a thin layer of bismuth (Bi) is pre-deposited on the Mo-coated glass before the deposition of the Cu2ZnSnS4 to optimize the properties of the Cu2ZnSnS4 thin film and the performance of corresponding solar cell. It is found that the pre-deposition of Bi leads to the improvement in the crystallinity of synthesized Cu2ZnSnS4 film as evidenced by large grain sizes and less grain boundaries. Photoluminescence measurement indicates that the recombination in the film is inhibited as the reduction of the boundaries which is always regarded as the recombination centers of the carriers. Besides, the reaction of Zn into CZTS lattice is promoted with the decrease of the second phase ZnS. In addition, the inserted Bi layer blocks the diffusion of S atoms into Mo with the reduced thickness of MoS2 at CZTS vertical bar Mo interface. It decreases the cell series resistance. Because of the improvements above, the performance of the cell with pre-deposited Bi is boosted. (C) 2015 Elsevier B.V. All rights reserved.