Preparation And Characterization Of Polysilicon Thick Films On Graphite Substrate

Polysilicon(poly-Si)film solar cell that combines the excellent performance of crystalline silicon solar cell with thin film solar cell is the most promising photovoltaic cell,which has not only the light stability and the comparable photoelectric conversion efficiency of the crystalline silicon solar cell,but also has the advantages of less consumption of the thin film solar cell materials and low cost.In this paper,polished graphite plates were selected as the substrate materials.The theoretical thickness of the high efficiency poly-Si film solar cell was calculated.The poly-Si thin films were prepared by magnetron sputtering,rapid thermal annealing and conventional annealing,and the thin film quality was analyzed by XRD,Raman and SEM.The influencing factors of poly-Si thin films prepared by aluminum-induced crystallization and magnetron sputtering at high temperature were studied emphatically,and the optimum process conditions were determined.The poly-Si thick films were grown on seed layer by CVD,and the solar cell was initially prepared on the thick films.The important results obtained are as follows:(1)In order to produce high efficiency poly-Si film solar cell,the theoretical thickness of 40?50?m is more appropriate according the perspectives of light absorbing capacity of poly-Si and the minority carrier diffusion length(2)The poly-Si thin film seed layers were prepared by aluminum-induced crystallization and inverted aluminum-induced crystallization respectively.The test results show that the poly-Si thin film prepared by inverted aluminum-induced crystallization had larger grain size and better crystal quality compared to aluminum-induced crystallization.The process of preparing poly-Si thin films by inverted aluminum-induced crystallization were optimized systematically and obtained the optimum condition:substrate temperature of amorphous silicon was 550?,the Al/Si thickness ratio was 0.5,the annealing temperature was 520?,and the annealing time was 10h;The comparative experiments of amorphous silicon films crystallized by conventional annealing and rapid thermal annealing were made,which found that the poly-Si thin film had a smaller grain size although the rapid thermal annealing can crystallize the amorphous silicon in a short time.Based on these factors,an aluminum-induced crystallization model was established,which can well explain the influence of these factors on the production of poly-Si thin films.(3)The poly-Si thin films were prepared by magnetron sputtering at high temperature.The results show that 690? is the critical substrate temperature for the crystallization,the thin films prepared in the range of 690?875 ? have strong Si(220)preferred orientation,then the Si(111)crystal face takes advantage at 890?,but the Si(220)crystal face takes advantage again with the further increase of substrate temperature.The experimental results of crystallization of amorphous silicon thin film and the preferred orientation are explained by the principle of the lowest energy,Brava's rule and classical nucleation theory,and the three theories are unified(4)Experiments have shown that the poly-Si thick films deposited on the seed layer are uniform and orderly in comparison with those grown directly on graphite substrates,and have the same preferred orientation with seed layer.The preparation processing of thick film cell was preliminarily explored,and the poly-Si thick film cell with conversion efficiency of 10.12%was produced.