Simulation And Optimization Of Microcrystailine Silicon/Crystalline Silicon Hetero-Junction Solar Cells

Generally speaking, the microcrystalline silicon is made up of microcrystalline grain,amorphous phase and boundary ,its existence of micro-hole, and its optical band gap changes from 1.2eV to 1.7eV with the different crystalline volume fraction of films. Microcrystalline silicon thin film solar cell has the advantages of both crystalline silicon solar cell and thin film solar cell,so it is believed as the technology of silicon film solar cells in the next generation.This thesis focused on the study of the novelμc-si/c-si solar cell, the performances of HIT solar cells with different thickness of window layer, the density of interface defect states (Dit) ,the intrinsic layer,defect concentration and back surface field were simulated .AFORS-HET software was used in the simulation of theμc-si/c-si heterojunction solar cell. We chooseμc-si(p)/ c-si(n) solar cell according to the request of simulation. some meaningful results were achieved:(1)The modeling results show that open circuit voltage, short circuit current and efficiency decrease with increasing of thickness of window layer ,the optimal thickness of emitter layer about 5nm.However, the efficiencies firstly increase with increasing of the band gap energy, while the band gap energy increases to 1.6eV the efficiencies begin to decrease. Theμc-Si (p)/c-Si(n) heterojunction solar cell has a highest transit efficiency of 21.82% with optimum parameters, e.g. the thickness of window layer of 10nm, band gap energy of 1.6ev and doping concentration of 1019cm-3.The main role of the intrinsic layer is to passivate the surface states of c-Si wafer, open circuit voltage, short circuit current and efficiency decrease with increasing of thickness of intrinsic layer ,the optimal thickness of intrinsic layer about 5nm. the defects concentration of the i-layer affect the I-V characteristics and spectral response at long wavelength importantly.(2) Back surface field ( BSF ) effect ofμc-Si(p)/μc-Si(i)/c-Si(n) heterojunction solar cell was simulated by AFORS-HET software . The results show that the thickness of the BSF has slight influence on the performance of the solar cell. The short circuit current and translate efficiency increase with the band gap, but it also drops when the band gap reaches 1.6ev.The short circuit current and fill factor increase with the doped concentration. Theμc-Si(p)/μc-Si(i)/c-Si(n) heterojunction solar cell has the highest translate efficiency of 24.68% with the thickness of the BSF of 10nm, band gap of 1.6ev , and the doped concentration of 5×10¹⁹cm^-3.(3)The tandem solar cells have become the most competitive new generation solar cell across the world. We have developed a semi-empirical motel to calculate the conversion efficiency of a based two junction solar cells upon the performances of the component cells. Current matching is one of the key factors affecting the conversion efficiency of two-terminal tandem solar cells , then the highest efficiency of the two-terminal tandem solar cells of 36.1% can be reached with I_SC1 =I_SC2=33mA /cm².