SnO₂ Film Prepared By Chemical Bath And Its Perovskite Solar Cell

Perovskite solar cells(PSCs)have become one of the most promising solar energy conversion technologies for low cost and high photoelectric conversion efficiency(PCE).Planar PSCs with SnO₂ electronic transport layer(ETL)are widely concerned because of its simple process and low energy consumption.However,most technologies for SnO₂ ETL require relatively high annealing temperature(?150 ^oC),which hinders the industrialization and flexibility of PSCs.In this thesis,rutile SnO₂ ETL with high quality has been prepared via low-temperature chemical bath,and the photoelectric properties of SnO₂-based PSCs have been studied.Through the control of precursor SnCl₄ concentration and annealing temperature,the surface microstructures and optoelectronic performances of SnO₂ films are optimized.Uniform SnO₂ ETLs with high crystallinity and transmittance are obtained from 0.3 M SnCl₄ solution and 100 ^oC heat-treatment,which is positive to improve the electron transport speed and weaken recombination loss in SnO₂based photovoltaic devices.The maximum PCE of PSCs is 16.78%,and the hysteresis index(HI)is reduced from0.76 to 0.31.Secondary-bath modification with 0.035 M SnCl₄ is proposed to decorate SnO₂ ETLs(2-SnO₂(0.035)).The PCE of PSCs based on 2-SnO₂(0.035)film are enhanced to 17.71%.Simultaneously,HI of PSCs is reduced to 0.11,since secondary-bath refines the surface particles of ETLs,passivates the defects and reduces charge recombination on the interfaces between the ETLs and perovskite.What's more,the 2-SnO₂ based PSCs can remain 85.7%of the premier PCE after repositing in air for 60days.Then mixed perovskite(FAPb I₃)_X(MAPb Br₃)_1-X has been introduced.The PSCs based on 1.6 M(FAPb I₃)_0.85(MAPb Br₃)_0.15 achieve 19.22%PCE and 0.268 HI.In order to solve the hysteresis problem,2.5%?5%and 7.5%K⁺are doped into the mixed perovskite,respectively.The results show that the PCE of PSCs is the highest and the HI is the lowest when the doping ratio of K⁺is 5%.Then it is found that the introduction of halogens will affect the hysteresis and photoelectric properties of PSCs devices when K⁺is doped.By comparing the micro morphology,band gap and photoelectric properties of the devices when different halogens are introduced,it is found that KI doping is the best.The optimum PCE of 5%K⁺doped KFAMA based PSCs is 17.63%,and HI is reduced to 0.011.5%K⁺enters into(FAPb I₃)_0.85(MAPb Br₃)_0.15 in the form of partially free and partially substituted doping,which improves the grain size of perovskite,inhibits the formation of Frenkel defects and solves the hysteresis phenomenon of PSCs.Finally,compared with Cs⁺doping,K⁺doping can effectively inhibit the hysteresis of PSCs.At last,the 5%KI-FAMA perovskite interface is modified via 100mL isopropanol(IPA).The structure of PSCs is FTO/SnO₂/KI-FAMA/Spiro-OMe TAD/Ag.After IPA modification,the organic residues on the surface are removed,the size of perovskite grain increases,and the defect densities on the perovskite surface decrease.