Electrodeposition And Characterization Of Copper Bismuth Selenide Thin Films And Antimony Bismuth Selenide Thin Films

Currently, one of the hot research topics in solar cells is to look for new elements-abundant, environment-friendly and low-cost thin film absorber materials. Among various thin film fabrication technologies, the electrodeposition has advantages of low-cost, non-vacuum and high efficiency, which is suitable for preparation of thin film solar cells. Based on the the requirement of thin film materials for solar cells and the analysis of fabrication technologies above, this paper studies the electrodeposition and characterization of copper bismuth selenide and antimony bismuth selenide thin films, both of which are composed of abundant and cheap elements. The main research conclusions obtained are as following:1. Copper bismuth selenide thin films have been prepared from acid aqueous solution by electrodeposition for the first time. The electrochemical behavior of the film deposition has been studied using cyclic voltammetry, revealing that copper and bismuth both undergo an underpotential deposition into thin films. It is also found deposition potential and pH value affect the film composition and morphology greatly, while deposition temperature influences little. Thin films with compact morphology and the stoichiometric composition of Cu1.09Bi1.42Se3as well as the main crystal phase of Bi2Se3have been prepared at the deposition potential of-0.22V vs. SCE, temperature of25℃and pH value of1.5, showing an optical absorption coefficient of over5×10cm-1and a band gap of1.50±0.01eV. Several electric characterizations show the film p-type conductivity. The carrier concentration, carrier mobility, and resistance characterized by Hall test are2.5×1018-5.6×1019cm-3,0.16～1.40cm2·V-1·s-1and70.2～175.8Ω·cm, respectively. The photoelectrochemical test shows the well photo-voltage response for copper bismuth selenide thin films. Mott-Schottky test gives the flat band potential of-0.24±0.03V vs. SCE, and a carrier concentration of8.9×1019cm-3, which is in cordence with the Hall test result.2. Antimony bismuth selenide thin films have been prepared from acid aqueous solution by electrodeposition. The electrochemical behavior of the film deposition has been studied using cyclic voltammetry, revealing that bismuth undergoes an underpotential deposition into thin films, but the similar deposition behavior has not been observed for animony deposition; antimony, bismuth and selenium can co-deposite in the potential range of-0.60±0.30V vs. SCE. It is found that deposition potential and pH value affect the film composition and morphology greatly, while deposition temperature influences little. Thin films with compact morphology and the stoichiometric composition of Sbi.o3Bio.97Se3have been obtained at the deposition potential of-0.40V vs. SCE, deposition temperature of25℃and pH value of1.5. After annealing treatment, films have inconspicuous change in composition, but show improved crystallinity with the orthorhombic Pbnm(62) structure of Bi-doped Sb2Se3phase; they exhibit an optical absorption coefficient of higher than105cm-1and a band gap of1.12±0.01eV. The photoelectrochemical and Mott-Schottky tests show the annealed film maintain n-type conductivity, a carrier concentration of1.1×1019cm-3and a flat band potential of-0.40±0.03V vs. SCE as well as obvious photo-current and photo-voltage responses. In addition, it is also found that the atomic ratio of Sb to Bi in films (Sb/Bi) has great influence on the crystal structure and optical characterization of the antimony bismuth selenide thin films:with the increase of Sb/Bi ratio, the films gradually convert from the rhombohedral R-3m(166) structure of Sb-doped Bi2Se3phase to the orthorhombic Pbnm(62) structure of Bi-doped Sb2Se3phase, where the latter films have larger optical absorption coefficients (～105cm-1) and band gaps (0.90-1.12eV).