Study On Photocatalytic Assisted Interface Passivation Of CIGSe Thin Films

CIGSe thin film solar cells have attracted extensive attention due to their high conversion efficiency,strong radiation resistance,stable performance,high light absorption coefficient and low cost.At present,the highest conversion efficiency of CIGSe thin film solar cells is 23.35%,which is considered as one of the solar cells with great development potential.There are two methods to prepare CIGSe thin films:vacuum method and nonvacuum method.The electrodeposition method is widely used to prepare CIGSe thin films by nonvacuum method because of its simple process,fast deposition rate,low equipment cost and high material utilization rate.The highest efficiency of CIGSe thin film solar cells prepared by this method is 17.3%.One of the factors limiting the efficiency improvement of CIGSe thin film solar cells prepared by selenidation after electrodeposition is the post selenidation process.The traditional one-step post selenidation process is easy to cause the aggregation of Ga back in the selenidation process,which makes the back interface defects of CIGSe thin film increase;The interface recombination of CIGSe/Cd S heterojunction is serious.At the same time,due to the lattice mismatch between Mo and CIGSe,a large number of defect states at the back interface are also caused.This thesis focuses on the appeal issue,and the main research contents are as follows:On the basis of one-step selenidation process,this thesis adopts the method of lamp heat assisted one-step selenidation,that is,in the post selenidation process,the halogen lamp is used to periodically irradiate the film surface,so that the surface temperature can quickly rise to 550℃,which solves the problem of Ga gathering towards the back and the poor crystal quality of CIGSe film,and improves the collection of back field carriers.At the same time,by controlling the time and frequency of heat auxiliary treatment of the lamp,it is ensured that the soda lime glass will not be deformed due to excessive temperature,which will affect the contact between Mo/CIGSe back interfaces.Through process optimization,CIGSe thin film solar cells with a conversion efficiency of 9.14%were obtained under the condition of two times of lamp thermal auxiliary treatment（each time for 1 min）.The energy of ultraviolet light is between 3e V and 124e V.By irradiating the surface of CIGSe film with high-energy ultraviolet light,the chemical bond on the surface of CIGSe film can be changed,making the surface of CIGSe film in an excited state,which is conducive to the reaction.At the same time,ultraviolet light will break the chemical bond between macromolecules（such as O molecules and N molecules）in the atmosphere,and improve the activity of gas molecules.The excited surface of CIGSe film will react with highly active gas molecules,so that the surface of CIGSe film can undergo passivation reaction at a lower temperature.In order to reduce the interface recombination of CIGSe/Cd S heterojunction,ultraviolet light is used to irradiate the surface of CIGSe film in vacuum,air and N₂ atmosphere respectively for30min,which improves the chemical reaction activity of the surface defect location of CIGSe film,and makes it react with the active substance in the atmosphere at low temperature,so as to achieve the purpose of passivating the surface defects.Finally,the conversion efficiency of CIGSe thin film solar cells was increased from 9.14%to 10.68%after ultraviolet treatment in N₂atmosphere for 30 min.To solve the problem that the lattice mismatch between Mo and CIGSe leads to a large number of defect states at the Mo/CIGSe back interface,this thesis uses SCAPS software to establish a Mo/CIGSe/Cd S/Zn O/Al:Ni battery structure,and introduces a Mo(O_xSe_1-x)₂ transition layer between Mo and CIGSe absorption layers.The first principle calculation shows that Mo Se₂ is a direct band gap semiconductor with a band gap of 1.44 e V.When the oxygen content increases from 0%to 50.0%,the band gap of Mo(O_xSe_1-x)₂ changes from 1.44 e V to 0.77 e V.The influence of Mo(O_xSe_1-x)₂transition layer on CIGSe solar cells was studied using SCAPS software.The simulation results showed that when the thickness of Mo(O_xSe_1-x)₂ layer was 40nm and the oxygen doping concentration was 25%,the band gap of Mo(O_xSe_1-x)₂layer was 1.08e V,and the conversion efficiency of CIGSe solar cells was increased from 15.80%to24.35%,providing a theoretical basis for solving the problem of back interface recombination of CIGSe.