Simulation Of Copper-based Compound Thin Film Solar Cells

In recent years,the low-cost and non-toxic absorber materials to replace CIGS is drawing attention in the research of thin film solar cells.Some copper-based compound semiconductor materials such as Cu₂ZnSnS₄,Cu₂SnS₃ and CuGaS₂ are favored by researchers because of their good optoelectronic properties.The material is generally a direct band gap material with a high absorption coefficient,and its various fabrication process and easier to mass production.However,the PCE of single-junction cells prepared by these materials is much lower than the SQ limit?more than 30%?,thus there are still ample room for development.Some related reports showed that the alloying Se can tune the bandgap?0.95?1.5eV?of Cu₂ZnSnS₄ effectively improving the performance of CZTS solar cells.Similarly the alloying Ge can also tune the bandgap?0.91?1.56eV?of Cu₂SnS₃,which can overcome the shortcomings such as low V_oc,high hole concentration and low mobility.In addition,doping Ti or Cr can introduce an intermediate band in the wide bandgap CGS material,adding multiple photonic channels to effectively improve the current density without reducing the output voltage.The PCE of the intermediate bandgap solar cell?IBSC?is expected to surpass the SQ limit of single-junction cell.This paper intends to use SCAPS simulation software to simulate and optimize the solar cells of the above materials as the absorption layer,thus providing guidance for the experiment.The innovative results obtained in this paper are as follows:1.Construct a Cu₂ZnSn?S,Se?₄ thin film solar cell model,and investigate the effect of the absorber thickness,carrier concentration,defect state,Se/?Se+S?composition,and the buffer CdS carrier concentration and thickness on cell performance and the simulation optimization of the absorber bandgap gradation structure,under standard illumination conditions.The optimized cell parameters are given:the absorber thickness of 2.5?m,Se/?Se+S?composition of 0.5?0.6,acceptor concentration of 10¹⁷cm^-3,threshold defect concentration of 10¹⁶cm^-3,the donor concentration of the buffer of5×10¹⁷cm^-3 and the thickness of 40-50 nm.The optimum bandgap gradation parameters of 0-0.56 is obtained,which effectively improved the PCE by at least 4%compared to the optimal uniform bandgap,thus verifying the superiority of the post-segregation structure.The pre-segregation and double segregation structures are less obvious due to the high CBO of the CZTSSe/CdS interface.2.Construct a Cu₂?Sn,Ge?S₃ thin film solar cell model,and investigate the effect of the work function of the back contact,the Ge/?Ge+Sn?composition of the absorber layer,the thickness,the carrier concentration,the defect state,the electron affinity of the buffer,and CdS thickness on cell performance and the simulation optimization of the absorber bandgap gradation struture.The optimization parameters calculated are as following:the back contact work function of more than 5.2e V,the Ge/?Ge+Sn?component of 0.3?0.5,the absorption layer thickness of 3.5?m,the carrier concentration of 6×10¹⁶cm^-3,and the threshold defect concentration of 10¹⁶cm^-3 and the buffer thickness of 30?40nm,the electron affinity of 4.35eV.The optimum bandgap gradation parameters of 0.9-0.3 is obtained,with the optimal PCE of 19.03%.The double gradation structure is only possible to improve cell performance when its energy inflection point is in the depletion region,and the highest PCE of 19.9%is obtained.3.Construct a Ti-doped CGS multi-bandgap thin film solar cell model,and investigate the effects of back surface field,impurity level and doping concentration on cell performance.The calculation results show that the effect of the back surface field significantly improves the photocurrent density,effectively improving the PCE by 3.1%.The results of Ti being the best element for CGS multi-bandgap cells have been validated and with efficiencies as high as 30%obtained.The increase in Ti doping concentration can effectively increase the photocurrent density.