Post-annealing Process Of Sb₂Se₃ Films And Thin-film Solar Cells

With the development of industry,the average annual emissions of carbon dioxide and other greenhouse gases have increased year by year,which has caused global problems,such as climate warming,abnormal temperatures,and frequent extreme weather.As the primary choice for low-carbon energy,solar energy can be converted into electricity by the solar cell.Antimony selenide(Sb₂Se₃)is a new type of thin-film solar cell material with stability,low toxicity and abundant reserves,which has the advantages of suitable forbidden bandgap(1.17 e V),high absorption coefficient(10⁵ cm^-1),low crystallization temperature(133?),and single phase.As a result,Sb₂Se₃ has great potential for development.However,the current technologies of the preparation of Sb₂Se₃ solar cell still have the following problem.On one hand,the distance between the evaporation source and the substrate is limited,so there is large temperature crosstalk,and the difference of temperature between them cannot be maintained for a long time.Hence the crystallization time of the film is limited,which restricts the grain size of the Sb₂Se₃ film.On the other hand,the excessively high evaporation temperature increases the vapour pressure of the Se component,and promotes the decomposition of Sb₂Se₃,making the film depleted in Se.Both theory and experiment show that the lack of Se will cause the generation of deep energy level defects such as vacancy(V_Se)and substitution(Sb _Se),which promotes carrier recombination,significantly reduces the minority carrier life of Sb₂Se₃ and efficiency of Sb₂Se₃ solar cells.The technologies of high-temperature post-annealing and Se-compensation are the keys to solving the problems above.This article will work from the following two aspects.(1)High-temperature post-annealing treatment with a certain atmosphere.The influence of the parameters of pressure,temperature and time on the morphology of the Sb₂Se₃ film is understood,through the analysis of the reasons for the formation of light-transmitting holes in the Sb₂Se₃ film under low-pressure conditions.After gradually adjusting the parameters of post-annealing pressure,temperature and time,the final selection of post-annealing pressure 1×10⁴ Pa,the annealing temperature is 350?,the annealing time is 30 min,and a high-performance device with a conversion efficiency of6.8%is fabricated.It has the highest efficiency so far without the hole transport layer on TiO₂.In this process,the annealing processes are explored through material characterization and electrical testing.This article analyzes the effect of post-annealing of Sb₂Se₃ film on device performance,by X-ray Diffractometer(XRD),Scanning Electron Microscope(SEM),Ultraviolet-visible Spectrophotometer(UV-vis),Film Light Response(PD),Current and Voltage test(J-V),Capacitance Voltage test(C-V),Capacitance Frequency test(C-f),Light Intensity Dependent Device Performance test and other physical tests.(2)High-temperature post-annealing treatment with Se-compensation.The Se atmosphere is added during the annealing process to form a good stoichiometric ratio,to avoid the adverse effects of high-vapour-pressure elements leaving the system and the segregation of film.First,use Se grains as the Se source for post-annealing.The annealing pressure is 10⁴ Pa,the annealing temperature is 400?,and the annealing time is 30 min.The element ratio 2[Se]/3[Sb]is 0.967,which is close to the stoichiometric ratio.And the device efficiency is 5.16%,slightly higher than that of the unannealed sample by 5%.Another selection is using Sb₂Se₃ as a Se source to post-anneal.When the annealing pressure is 1×10⁴ Pa,the annealing temperature is 400?,and the annealing time is 60 min,the device efficiency is increased to 5.3%.However,the element ratio of 2[Se]/3[Sb]is 0.887,proving that the effect of supplementing Se by this method is poor.Theoretical analysis shows that the main component of Se element and Sb₂Se₃ is Se_n(n>2)at high temperature,so H₂Se is the best Se source.In the end,the article puts forward an experimental idea for Se post-annealing by H₂Se.