Study On The Synthesis And Properties Of Buffer Layer For Cu₂ZnSnS₄Thin Film Sotar Cells

With the modern industry speeding up, the demand for traditional fossil fuelsincreases which makes the environmental problems more and more serious, so welook forward to a kind of clean energy to replace the traditional fossil fuels. Amongthe numerous green energy, solar energy is a very promising clean energy which isconverted into electrical energy by the solar cell. In the recent years, Cu2ZnSnS4(CZTS) quaternary compound has become the hottest absorption layer material ofthin film solar cell. Because it costs lower, the elements contented is harmless and theabsorption coefficient (>104cm-1) is high. In order to form the P-N junction with theP-type CZTS to separate the photo-generated carriers, we need to prepare a layer ofN-type semiconductor thin film. The CdS thin film is one of the widely used n-typesemiconductor thin film. The Chemical Bath Deposition method (CBD) has severaladvantages such as its mild preparation conditions, its lower cost and preparing highperformance semiconductor thin films widely. So, the CdS thin film and theabsorption layer are used to form the heterogeneous P-N junction to prepare highperformance thin film solar cells in the recent years.This paper referenced the experiences from the research group which wasstudying the absorption layer and window layer in the solar cell to study the solarcell’s CdS thin film buffer layer. This paper adopted the CdSO4, CS(NH2)2, andNH4.H2O as the reaction reagent, using the Chemical Bath Deposition method (CBD)to grow the CdS N-type semiconductor thin film on the glass substrate. Then we made annealing treatment to the films under the nitrogen atmosphere. We changed thedosage of the three kinds of reaction reagent to change the reactive ion’sconcentration in the solution, finding out the optimal growth conditions for the CdSthin film obtained.The X-ray diffraction (XRD),scanning electron microscopy (SEM)and UV-vis absorption spectroscopy were developed to characterize the CdS film’scrystal quality and physical properties’ relationship with different test conditions,such as the reactive ion’s concentration, the PH value, the deposition time, annealingtemperature and so on. From the crystal structure, surface morphology and opticalproperties to analyze, we got the following conclusions:(1) In the CdS thin film growth process, the thickness of the film reached themaximum of150nm when the deposition time reached50min and didn’t change anymore with the deposition time.(2) When the deposition temperature was65℃, according to the XRDanalysis the solution was the most favorable for the growth of the CdS six-partycrystal phase, forming a dense, uniform and high light transmittance CdS thin film.The thin film’s crystallinity improved with the increase of the deposition temperature,but the transmittance of the visible light dropped from90%to around65%with thethe forbidden band width narrowing down.(3) The PH value of the solution affected the surface morphology of the CdSthin film largely, and the density of the CdS thin film was the best when the PH=9.824.(4) The annealing treatment was beneficial to the CdS thin film’srecrystallization, but didn’t change the CdS thin film’s crystal structure. Theexperiment proved that the CdS thin film’s recrystallization was best when theannealing temperature was350℃.