Preparation And Structure Optimization Of CuSbSe₂ Thin Films By Electrodeposition

Copper antimony selenium（CuSbSe₂）is a direct band gap semiconductor.As a new generation of thin film solar cell absorber layer material,it has the characteristics of band gap adjustable from 1.09 to 1.2e V,high light absorption coefficient(>10⁵cm^-1)and low grain generation temperature（300～400℃）,which is very suitable for the preparation of flexible photovoltaic devices.This paper focused on the preparation of CuSbSe₂ thin films by pulsed electrodeposition followed by selenization.The growth mechanism,film delamination phenomenon and structure optimization of solar cells were investigated.The details of the study are as follows:A good quality CuSbSe₂ absorber layer is the key to prepare high performance solar cells.In this paper,the phase evolution of CuSbSe₂ thin film was studied in detail by adjusting the annealing temperature during post-selenization in the range of280～420℃.The growth mechanism was concluded as Cu and Sb react with Se to form Cu₂Se and Sb₂Se₃ respectively,and both continued to react to form CuSbSe₂.During the study,it was found that a large number of Cu₃Sb Se₄ heterogeneous phases were formed during the growth of the film,and the CuSbSe₂ film showed a delamination phenomenon.The growth process was further investigated by controlling the selenization time in the range of 2～50 minutes.The selenization reaction was found to occur from the upper surface of the film,with uneven distribution of film elements and a copper-rich phase on the upper surface,preferentially generating the Cu₃Sb Se₄heterogeneous phase.In order to solve this problem,this paper adjusted the heating rate to reduce the aggregation of Cu on the upper surface and suppress the generation of Cu₃Sb Se₄ heterogeneous phase,which effectively improved the delamination of CuSbSe₂ films and obtained CuSbSe₂ films with relatively single composition and good crystallinity.Finally,CuSbSe₂ thin film solar cells with the highest photoelectric conversion efficiency of 1.40%were obtained.Inappropriate band offset between the absorber layer and the Cd S buffer layer deteriorates the device properties of CuSbSe₂ solar cells.In this work,the effects of Cd_1-xZn_xS and Zn O_yS_1-y buffer layers on the performance of CuSbSe₂ solar cells were studied with SCAPS simulation.The influence of Zn/（Zn+Cd）ratio,O/（O+S）ratio,thickness,donor density of Cd_1-xZn_xS and Zn O_yS_1-y buffer layers,substrate and operating temperature on the performance of the solar cell were investigated.The conduction band offset（CBO）of the interface between buffer layer and absorber layer was optimized.Efficiency of 7.81%of CuSbSe₂ devices were obtained with Zn/（Zn+Cd）=0.5 and the thickness of 20nm of Cd_1-xZn_xS buffer layers.Efficiency of 10.26%of CuSbSe₂ devices were obtained with O/（O+S）=0.6 and the thickness of 30nm of Zn O_yS_1-y buffer layers.Besides,the efficiency of Cd_1-xZn_xS/CuSbSe₂ solar cells first increased and then decreased with the increase of donor density,while the efficiency of Zn O_yS_1-y/CuSbSe₂ solar cells continued to increase to saturation.The high work function material formed an ohmic back contact with the absorber layer,and the work function of the material needed to be no less than 5e V.The increase in operating temperature had a negative impact on the performance of the solar cells,leading to a linear decay in cell efficiency.