Preparation Of Copper Indium Selenium And Copper Indium Gallium Selenium Thin Films And Its Energy Band Calculation

Copper indium selenium thin-film solar cell with advantages of high conversion efficiency, low manufacturing cost and stable battery performance. CuInSe2 as an absorbing layer is a material with direct bandgap about 1.04eV, less than ideal band gap 1.5eV. By doping an appropriate amount of Ga in the CuInSe2 to replace part of the indium element so that the band gap can be adjusted within the range of 1.04-1.7eV, and CuIn1-xGaxSe2 thin film is the most promising material.Firstly, establish the physical model of CuInSe2 and CIGS doped with different concentrations of Ga, and then the CuInSe2’s band gap based on the model was calculated. Different pseudopotential was used to calculated, the results obtained were compared with the theoretical values. By analyzing the results, CuInSe2 and CIGS bandgaps calculated herein are smaller than the theoretical value. Results showed that the band gap becomes larger with the doping concentration increasing calculated by LDA and PBE, which is accordance with the experience curve of doping concentration and the band gap.Spin coating-chemical co-reduction is an easy-operate and low-cost method for preparing CIS. CIS and CIGS thin films were synthesized by spin-coating chemical co-reduction herein. The effects of different conditions for preparing CuInSe2 thin films were investigated by XRD and SEM. Analysis the influence of changing the reaction time at the same temperature on CuInSe2 thin films. Results showed that long reaction time is good for the crystallization of the film at the same experimental temperature, and film was detected contain Cu, In and Se elements by EDS. The effect of reaction times on CuInSe2 films were investigated, and increasing reaction times is good for crystallization, which can also make films more compact, higher electrical conductivity and decrease the band gap. Estimated band gap of CuInSe2 film is about 1.2eV by extrapolation method, larger than the theoretical value 1.04eV.CIGS thin films were synthesized by spin-coating chemical co-reduction. The effects of reaction temperature and time for preparing CIGS thin films were investigated by XRD and SEM. Observing the morphology of CuIn1-xGaxSe2 films, it can be seen that with increasing of doping concentration, its surface morphology changes, there is a conversion from spherical to rod crystal. By testing the resistivity of CuIn1-xGaxSe2 thin films, it is concluded that the effect of doping concentration on the resistivity is not very obvious, but increasing slightly. The absorbance of CuIn1-xGaxSe2 thin films was tested by visible spectrophotometer, and the band gap of the thin films were estimated. The estimated optical band gap of the CuIn0.8Ga0.2Se2, CuIn0.6Ga0.4Se2, CuIn0.4Ga0.6Se2, CuIn0.2Ga0.8Se2 and CuGaSe2 thin films are 1.25eV,1.3eV,1.33eV,1.38eV and 1.4eV. The results show that the band gap of CuIn1-xGaxSe2 films value is larger than the theoretical value, but it is consistent with the doping variation.