Preparation And Performance Research Of Novel Dualistic Selenide Thin Film Solar Cells

The over-exploitation and use of the traditional fossil energy sources have caused serious environmental pollution,so the solar energy have received extensive attention as a clean and renewable energy source.Solar cells are an effective device for converting solar energy into electrical energy.Among them,thin-film solar cells are rapidly developing due to the advantages of low cost,good stability,high efficiency,device lightweight,miniaturization and flexibility.At present,the copper indium gallium selenide and cadmium telluride thin-film solar cells have achieved high power conversion efficiency.However,due to the rare or toxic elements in the raw materials,it is difficult to achi eve large-scale promotion and application.Therefore,researchers are committed to developing new thin-film solar cells with low cost and low toxicity.Among them,binary selenide antimony selenide（Sb₂Se₃）and germanium selenide（Ge Se）have become research hotspots in the field of solar cells in recent years due to large raw material reserves,green non-toxic,low price and stable photoelectric performance.To date,the power conversion efficiency of Sb₂Se₃ and Ge Se is far lower than the theoretical Shockley-Queisser limit efficiency（>30%）,which has great potential for improvement.This thesis focuses on the improvement of performance based on Sb₂Se₃ and Ge Se solar cells.The main contents include:（1）The efficiency of Cd S/Sb₂Se₃ solar cells was improved about 30%after ultraviolet ozone（UVO）treatment Cd S buffer layer.The functional layer Cd S in Sb ₂Se₃solar cells is generally prepared by chemical water bath deposition（CBD）.However,the surface of the Cd S films prepared by this method is prone to residual impurities in solution,resulting in a large number of defects at the interface between Cd S and Sb ₂Se₃,thus causes low device performance.In this paper,we propose to perform Cd Cl ₂ activation and UVO treatment successively on Cd S films deposited by CBD method.The effects of UVO treatment on crystallinity,surface morphology and photoelectrical properties of Cd S films were systematically investigated.The results show that the treated Cd S film significantly improves the surface coating coverage and crystallinity,substantially reduces the residual organic impurities on the film surface,and enhances the electrical conductivity.In addition,the defects between the interface of Cd S and Sb₂Se₃ are significantly reduced and the carrier recombination probability is decreased.The device performance is significantly improved with the Cd S buffer of UVO treatment in Sb₂Se₃ solar cells.（2）A novel Cd Se/Ge Se solar cell was constructed by using Cd Se nanocrystals as the buffer layerthen achieve the control of Ge Se absorber layer orientation.Cd S is generally selected as the buffer layer materials in Ge Se solar cells.However,the Ge Se films prepared on the Cd S substrate have a crystal plane orientation dominated by（400）,which is not favorable for carrier transport.Therefore,it is imperative to develop new buffer layer materials.In this paper,Cd Se nanocrystals were prepared by the solvothermal method and used as a buffer layer for Ge Se solar cells.The results show that the orientation regulation of Ge Se films was achieved on Cd Se nanocrystals,and the Ge Se orientation changed from parallel growth[400]to perpendicular to the substrate[111].This orientation change is more conducive to efficient carrier transport in the middle layer of the solar cells.In addition,first-principles calculations also demonstrate that the formation energy of Ge Se in the[111]orientation was lower than that in the[400]orientation.Finally,the superstrate FTO/Cd Se/Ge Se/Au solar cell was constructed with a power conversion efficiency of 0.48%and good stability.（3）Non-toxic Sn O₂ quantum dots were used as the buffer layer to induce the growth of Ge Se along the[111]orientation,and the Sn O₂/Ge Se thin-film solar cells with an efficiency of 0.51%were obtained.Cd S and Cd Se contain the toxic element Cd,which is harmful for human health and environment.Therefore,in order to construct the whole green and non-toxic device,this paper selects non-toxic Sn O₂ quantum dots as the buffer layer in Ge Se solar cells and constructs superstrate FTO/Sn O₂/Ge Se/Au thin-film solar cells.The formation energies of[400]and[111]orientations of Ge Se thin films grown on Sn O ₂buffer layer are calculated by first-principles calculations,respectively.It is found that the formation energies of[111]orientation are lower than those of[111]orientation,indicating that[111]orientation Ge Se films were more likely to grow on Sn O ₂ buffer layer,which was consistent with the experimental results.The performance of the constructed Sn O₂/Ge Se heterojunction solar cells was investigated with good stability.