The Influence Of Post Treatment Processes On Optic-electric Properties Of CuInS₂ Thin Film And Solar Cells

Copper indium sulfide(Cu In S2) is one of the most important I-III-VI2 semiconductor compounds with direct band gap about 1.5e V, which is very close to the best band gap of solar cells around 1.45 e V. Cu In S2 is an ideal material for solar cells with many unique advantages, such as non-toxic, good radiation resistance ability, good stability etc. Furthermore, absorption coefficient of Cu In S2 is as high as 105cm-1.In this paper, single source evaporation method has been applied to prepare Cu In S2 films. Moreover, the influence of the post treatment processes on optical-electrical properties of Cu In S2 thin films has been studied. Then, the solar cell consisted of glass/Mo/Cu In S2/Cd S/i-Zn O:Zn O(Al)/Al is studied in the same time. The structures, the morphologies and the optical-electrical properties of Cu In S2 films are studied using XRD, SEM, UV-vis Spectroscopy, AFM and Raman Spectroscopy. Main conclusions are shown in below:1. Dense-uniform-continuous Cu In S2 thin films are prepared by vacuum evaporation. After annealed at 400°C in sulfur atmosphere for 30 min, polycrystalline Cu In S2 thin films have a preferred(112) orientation with chalcopyrite structure, and the photo-electric properties of these films simultaneously improved significantly.2. The bombardment of Argon plasma ion on the surface of Cu In S2 thin films can effectively improve the optical absorption coefficient of these Cu In S2 thin films with the decreasing surface roughness and the increasing density. Furthermore, the CuxS secondary phase also can be removed effectively. With the increase of the bombardment time, the resistivity of these films decreases.3. The CuxS secondary phase can be removed effectively by etching of bromine methanol solution. 10μl bromine and 25μl bromine are mixed with 100 ml methanol solution, respectively, to form two corrosive agents with different concentrations. Through XRD and AFM measurement, the results show that the resistivity of these film decreases with the increase of etching time. In the same time, the absorption coefficient increases and the surface roughness decreases.4. Optimal processes parameters of Mo, Cd S and Zn O thin films are obtained. The back electrode Mo thin films with good adhesion and low resistivity are deposited by magnetron sputtering method. Furthermore, two detailed processes are given: 80 W deposition power, 1.4Pa Ar pressure for 1min, and 60 W deposition power, 0.2Pa Ar pressure for 10 min. Uniform-continuous buffer layer Cd S thin films are prepared by chemical bath deposition, and the optimal process is given in below: 20 ml of 0.1 mol/L Zn(NO3)2, 0.5ml NH3?H2O, 2ml of 1mol/L ammonium acetate, and 20 ml of 0.2mol/L sulfocarbamide are mixed to be heated at 80 oC for 1 hour. Window layer i-Zn O with high light transmittance and Al-Zn O thin films with low resistivity are prepared by magnetron sputtering method, and the detailed process is exhibited: sputtering power of 160 W, Ar pressure of 1.3Pa for 10 min and 30 min.