Simulation And Preparation Of BaSi₂ Solar Cells

As a new type of solar cell material,BaSi₂ has the advantages of suitable and adjustable band gap,high light absorption coefficient,and controllable electron and hole concentration,giving rise to its great potential in thin-film solar cells.In view of the low photoelectric conversion efficiency of current BaSi₂-based solar cells,and by using numerical simulation combined with theoretical analysis,this work systematically studies the transport performance of BaSi₂-based homojunction and heterojunction solar cells,in order to provide theoretical guidance for the preparation of environmentally friendly,cheap and high conversion efficiency BaSi₂-based solar cells.On the other hand,considering the high cost and low rate of molecular beam epitaxy,and the unbalanced ratio and poor crystallinity of film deposited by magnetron sputtering technology,research on BaSi₂ thin film prepared by magnetron sputtering method was also carried out.The details are as follows:The contact barrier height on performances of p-Si/n-BaSi₂ heterojunction,p-BaSi₂/n-BaSi₂ homojunction and p-Si/i-BaSi₂/n-Si heterojunction solar cells was investigated.Compared with the p-Si/n-BaSi₂ heterojunction,the p-BaSi₂layer in p-BaSi₂/n-BaSi₂ homojunction solar cell needs to be designed thinner due to the high light absorption coefficient of BaSi₂.Therefore,the height of front contact barrier has great influence on device performance.For p-Si/i-BaSi₂/n-Si heterojunction solar cells with N_A lower than 1×10¹⁹ cm^-3,the photoelectric conversion performance is mainly affected by the height of front contact barrier.The back contact barrier height merely has little effect on its photoelectric performance.Under ideal conditions of effectively eliminating Urbach tails and defects,the open-circuit voltage ofα-Si/BaSi₂/α-Si pin heterojunction solar cells can reach 1.131 V.The effects of film thickness,doping concentration and contact barrier height on performances of BaSi₂-based np or nip homojunction solar cells were investigated.It is found that the doping concentration and thickness of n-BaSi₂have decisive influences on photoelectic performances of n-BaSi₂/p-BaSi₂homojunction solar cells,low doping concentration or thin n-BaSi₂ layer is more beneficial in achieving high light conversion efficiency.For BaSi₂ nip homojunction,p-BaSi₂ layer with high doping concentration and slightly thicker film thickness is more beneficial to improve the built-in potential and thus V_oc of the solar cells.The contact barrier height between n-BaSi₂ and front electrode has a great influence on the photoelectric performances of BaSi₂ nip solar cells.For nip homojunction solar cells with thick p-BaSi₂,the contact barrier height between p-BaSi₂ and back electrode has little effect on their photoelectric performances.The effects of doping concentration,electron affinity and interfacial defect density of different electron transport layers and hole transport layers on the performances of BaSi₂ based nip or pin heterojunction solar cells were investigated.When n-BaSi₂,Cd S,Sn O₂,Ti O₂,Zn O electron transport layers are used as window layers in BaSi₂-based nip solar cells,n-Zn O(20 nm,N_D=5×10¹⁹ cm^-3)/i-BaSi₂（2000 nm）/p-BaSi₂(100 nm,N_A=5×10¹⁹ cm^-3)heterojunction solar cell has the highest photoelectric conversion efficiency as high as 28.209%.When p-BaSi₂,Cu₂O,Ni O,Cu I,Cu SCN hole transport layers are used as window layers in BaSi₂-based pin solar cells,p-Cu SCN(20 nm,N_A=5×10¹⁹ cm^-3)/i-BaSi₂（2000 nm）/n-BaSi₂(100 nm,N_D=5×10¹⁹ cm^-3)heterojunction solar cell has the highest photoelectric conversion efficiency as high as 27.987%.When the interface density of ETLs/BaSi₂ or HTLs/BaSi₂ is higher than 1×10¹² cm^-2,the photoelectric conversion performance of the device decreases rapidly.In synthesizing BaSi₂ thin films by magnetron sputtering,under high sputtering power,Ba O was easily formed due to the high activity of the Ba ions that much Ba can hardly react with Si rapidly to form BaSi₂.Therefore,it is easier to prepare BaSi₂ thin films under lower sputtering power.Covering passivation layer is beneficial to reduce the generation of Ba O.The substrate temperature has a great influence on preparing BaSi₂ thin films.The optimum substrate temperature obtained in this experiment is 500℃.In this paper,systematic simulation studies on BaSi₂ thin film solar cells and preparation of BaSi₂ thin films by magnetron sputtering were carried out.The research results will provide helpful guidance for the design and practical preparation of high-efficiency BaSi₂ thin-film solar cells.