A Preparation Of High-efficiency Sb₂Se₃ Solar Cells By Vacuum Thermal Evaporation Method

In recent decades,global environmental problems have occurred frequently.Global environmental problems such as the rise of global temperature,the hole in the Arctic ozone layer and the El Nino phenomenon have repeatedly attracted the attention of the international community.In order to solve these environmental problems,the international community needs to find new energy sources to replace the traditional energy sources that cause serious environmental pollution.Therefore,solar energy,which has the advantages of green,environmental protection and sustainability,has entered the vision of the international community.The absorption layer materials of solar cells must have excellent optoelectronic properties,in addition,they also need to need to have the advantages of green,non-toxic,rich reserves and so on.Sb₂Se₃ is a new type of inorganic thin film photovoltaic cell absorption layer material with the above advantages.Sb₂Se₃ material has excellent optoelectronic properties,has attracted people’s attention in recent years because of its abundant raw materials,low toxicity and long service life.The heat treatment process of Sb₂Se₃ thin film has an important influence on the performance of the device.The traditional heat treatment method is secondary annealing after the deposited film is cooled.The cooling and reheating process may interrupt the growth of the original crystals in the deposited films,promote the nucleation and growth of new crystals,and lead to the deterioration of the morphology of the films.In addition,the uniformity of CdS film prepared by traditional chemical water bath method is poor,and it will produce a lot of waste water containing cadmium,which will cause serious heavy metal pollution to the environment.In order to solve the above problems,the effect of in-situ heat treatment in H₂S atmosphere on Sb₂Se₃ thin films and devices was studied,and the mechanism of H₂S treatment affecting the device performance was studied.On this basis,the preparation of CdS buffer layer by spin coating method was explored to improve the quality of CdS film and solve the problem of Cd wastewater.Finally,the photoelectric conversion efficiency of Sb₂Se₃ solar cell devices has been effectively improved.The details are as follows:（1）In this work,Sb₂Se₃ thin films were prepared by vacuum thermal evaporation,and the effect of in-situ heat treatment in H₂S atmosphere on the performance of the device was studied.The effects of annealing atmosphere（vacuum,H₂S）,annealing temperature and annealing time on the quality,carrier transport performance and device performance of Sb₂Se₃ thin films were compared.The results show that during in-situ annealing in H₂S atmosphere,some Se atoms on the surface of Sb₂Se₃ films are replaced by S atoms,and it can fill the defect of Se loss on the surface of Sb₂Se₃ films caused by high temperature reverse evaporation,which can effectively reduce the recombination of carriers in the films and prolong the lifetime of carriers.Through optimization,the photoelectric conversion efficiency of the device is improved from 4.31%to 5.22%.The device showed good stability and no obvious attenuation when it was stored in air for 20days.（2）In In order to improve the preparation process of CdS thin films,spin coating method was studied in this work.The performance of the device is improved by stoichiometric ratio control and surface modification.The spin coating solution based on organic solvent was prepared by dissolving cadmium acetate and thiourea in ethylene glycol methyl ether.CdS thin films with moderate grain size,smooth surface and uniform coverage were prepared,and CdS（O）thin films were prepared by stoichiometric control.The effects of doping concentration,film thickness and Cd Cl₂ treatment on the device performance are studied,and the photovoltaic performance of the device is significantly improved.Cd Cl₂ treatment effectively reduces the ideal factor and reverse saturation current density,improves the quality of CdS/Sb₂Se₃ heterojunctions and reduces the defects of CdS.O doping can obviously improve the contact between the buffer layer and the absorption layer and reduce the carrier recombination at the CdS/Sb₂Se₃ interface,which is beneficial to the carrier transport and collection.Through optimization,the photoelectric conversion efficiency of the final device is improved from 4.52%to 5.33%,which means that the preparation of CdS thin films by spin-coating method can effectively improve the performance of chalcogenide photovoltaic devices.In addition,compared with the traditional water bath method,spin coating method can greatly reduce the production of cadmium-containing wastewater,save cost,reduce waste and be more environmentally friendly.In summary,the in-situ heat treatment and annealing of Sb₂Se₃ thin films with H₂S can improve the quality of Sb₂Se₃ thin films and the optical and electrical properties of Sb₂Se₃ thin films more easily and effectively.The CdS（O）thin films prepared by spin coating can effectively improve the contact between the buffer layer and the absorption layer,reduce the carrier recombination at the CdS/Sb₂Se₃ interface,and improve the carrier transport and collection in the film.Through process optimization,the photoelectric conversion efficiency of Sb₂Se₃ solar cell is significantly improved.