Preparation Of CdS/ZnS Thin Film And Influence Of Its On The Performance Of CIGS Solar Cells

In the field of photovoltaic,crystalline silicon has been dominant for a long time.CIGS thin film solar cells have been widely concerned for their high efficiency,good stability and convenient integration of photovoltaic buildings.in CIGS solar cells,the introduction of Cd S buffer layer can reduce the energy band mismatch between CIGS thin film and TCO,and achieve a certain degree of interface passivation.however,the toxicity of Cd in Cd S buffer layer will cause serious environmental pollution.People are trying to find a Cd-free,low-cost thin film material,but also can reduce the band mismatch between CIGS film and TCO.Zn S thin film material is considered to be the best choice to replace Cd S film.at present,the efficiency of CIGS solar cells using Zn S film as buffer layer has reached 23.35%.in this paper,the effects of Cd Zn S and Zn S thin films with different thicknesses on the performance of CIGS solar cells were studied theoretically and experimentally by using SCAPS-1d software and chemical water bath method respectively.the physical mechanism of the performance of CIGS solar cells changing with the thickness of Zn S thin films was analyzed from the perspective of device physics.Firstly,the effects of Cd S and Zn S films on the performance of CIGS solar cells were studied by SCAPS-1d;at the same time,the effects of thickness and defect density of Zn S thin films on the device performance are simulated,the results show that:from the point of view of band structure and carrier,Zn S as buffer layer can achieve the same level of high efficiency CIGS solar cells as Cd S buffer layer.When the thickness of Zn S thin film is 40 nm,the conversion efficiency of 20.5%can be achieved.Then,Cd S+Zn S multilayer films and CIGS solar cells were prepared by chemical water bath?CBD?deposition,it was observed by SEM that the grains on the surface of CIGS absorption layer became better with the increase of thickness,it completely covers the holes on the surface of CIGS.Furthermore,I-V,EQE,C-V analysis of Cds+Zn S stack devices were carried out.it was found that with the increase of the thickness of the stack buffer layer,the Cd S+Zn S stack device was more stable,when the carrier concentration is from 1.23×10¹⁶cm-3to 1.5×10¹⁶cm-3,the barrier becomes wider and carrier recombination is reduced,the maximum open circuit voltage?VOC?of Cd Zn S stacked buffer CIGS solar cells is 635mv when the thickness of Cd S film is 30nm and the thickness of Zn S film is 39nm,the obtained CIGS device achieves 11.86%photoelectric conversion efficiency.Finally,Zn S thin films were prepared by chemical water bath method as buffer layer of CIGS solar cells.With the increase of deposition reaction time,the grain size of Zn S increases and the small grain clusters form large grains,which makes the thickness of the film increase,the band gap width of Zn S thin film is 3.66ev by UV-VIS-NIR spectroscopy.the high band gap Zn S buffer layer CIGS solar cell with 41nm thickness is prepared,in the wavelength range of 400nm-600nm,there is a good external quantum response spectrum,which can improve the short-circuit current density of the cell,as a result,the performance parameters of Zn S/CIGS solar cells are improved,and the conversion efficiency of CIGS solar cells with Zn S thin film as buffer layer reaches 9.87%.at the same time,the metastable effect under J-V condition was observed due to the particularity of Zn S material and the photo enhancement effect,and the device efficiency was finally stabilized at 11.83%.