Preparation Of Cu - Zn - Sn - Sn Solar Cell Buffer Layer By Chemical Water Bath And Its Properties

In the structure of copper zinc tin sulfide(CZTS) thin film solar cell, the buffer layer, as an important part, is located between the window layer and the absorbing layer. At present, the commonly used buffer layer materials are Cd S, Zn S, Zn Se, In2S3, etc.. There are many methods of buffer layer preparation, among which, chemical bath deposition is one of the most commonly used methods of buffer layer material preparation, with the advantage of simple preparation process, low cost of equipments and raw materials and good uniformity of films.Zn S and Cd S thin films were prepared by chemical bath deposition, the measures of X-ray diffraction, scanning electron microscopy, spectrophotometer, step profiler were adopted, and the effect of different reactant concentration, deposition time and deposition temperature on the thickness, crystal structures, surface morphologies and optical properties of Zn S were detailed studied. After process optimization, the optimal process conditions of Zn S and Cd S were achieved, and the properties of different components of the Cd1-xZnxS thin films were preliminarily studied.The main results of this dissertation were as follows:(1) The XRD pattern of Zn S thin films shows a typical sphalerite structure, and the growth process is Nucleation-Linear growth-Saturation. When the deposition time is one hour, and the deposition temperature is 80 ℃, the Zn S film has the best properties: The thickness of Zn S thin film prepared under this condition is 63.87 nm, the surface morphology is uniform and smooth, which has good compactness and adhesion, the average transmittance in visible spectrum is 81.80%, the optical band gap is 3.77 e V, which is suitable as the buffer layer of CZTS thin film solar cell.(2) The prepared CdS thin film shows a typical wurtzite structure. The effect of different process conditions on properties of Cd S thin films is similar to Zn S, but its growth rate is significantly higher than Zn S film. After lots of experiments, when the deposition time is 30 minutes, and the deposition temperature is 70 ℃, the Cd S film has the best properties: the thickness is 51.13 nm, the surface particle size is smaller than Zn S thin films, the surface morphology is compact and smooth, The transmittance spectrum shows an obvious ultraviolet absorption edge at about 520 nm, and the transmittance(>520 nm) is above 70%, the optical band gap is 2.48 e V, the conversion efficiency of the CZTS thin film solar cell is 1.4%.(3) As for the Cd1-xZnxS thin films, with the increase of the mixture ratio x, the crystal form of Cd1-xZnxS thin films gradually changed from hexagonal to cubic structure and the particles became larger and sparser. All films have high transmittance, and the optical band gaps of the Cd1-xZnxS thin films varied from 2.47 e V to 3.66 e V as the mixture ratio varies from 0 to 1, which can achieve the the purpose of regulating the band gap by changing the value of x.