Morphology Regulation And Stability Study For Tin-based Perovskite Solar Cells

In recent years,organic-inorganic hybrid perovskite materials have been widely investigated for their superior photovoltaic properties,and the power conversion efficiency(PCE)of perovskite solar cells(PVSCs)has exceeded from 3.8%in 2009to 25.5%at present.However,conventional perovskite materials contain around 35wt%of lead,which would cause an environmental pollution problem in future large-scale applications.Tin-based perovskite is regarded as the most prospective alternative materials due to lower exciton binding energy,as well as higher light absorption coefficient and carrier mobility.Additionally,the tin-based perovskite also possesses a narrow optical bandgap(1.2-1.4 e V),which is closer to the ideal bandgap in the Shockley-Queisser limit.Nevertheless,tin-based perovskite also has some non-negligible issues.Sn²⁺is easily oxidized to the more stable Sn⁴⁺,and leads to a high concentration of p-type self-doping in tin-based perovskite films,thereby contributing to severe non-radiative recombination losses.Then,the faster crystallization rate for tin-based perovskite makes it hard to form a uniform and dense film on the substrate,resulting in the PCE of tin-based PVSCs still lagging behind that of lead-based PVSCs.To address the above problems,this thesis enables the suppression of Sn²⁺oxidation and the improvement of film morphology via additive engineering so as to obtain high-efficiency and stable tin-based PVSCs.The specific research is as follows:The introduction of the bidentate ligand 8-hydroxyquinoline(8-HQ)into tin-based perovskite films finds that the O and N atoms in 8-HQ can simultaneously coordinate with Sn²⁺to generate strong interaction toward forming stable complexes,thus significantly inhibiting the oxidation of Sn²⁺to Sn⁴⁺.Moreover,introducing the semiconductor molecule 8-HQ effectively improves the quality of tin-based perovskite films,reducing the defect states and non-radiative recombination with balanced and improved electron and hole mobilities.Based on the bidentate coordination effect of 8-HQ,the optimized tin-based PVSCs has reached the best efficiency of 7.15%with significantly reduced hysteresis effect and good reproducibility.Lastly,the 8-HQ optimized device still maintains nearly 90%of the initial PCE after aging in a nitrogen glovebox for 800 h,and more than 40%of the initial PCE after aging in air for 32 h,showing good circumstantial stability.The ionic liquid 1-butyl-3-methylimidazolium bromide(BMIBr)featuring strong polarity,low-melting point and high-boiling point has been introduced into the tin-based perovskite precursor solution.The BMIBr with lower melting point will serve as a liquid domain for dissolving the tin-based perovskite composites in the Ostwald ripening effect by its intrinsic liquids properties.During the thermal-annealing of tin-based perovskite films,the smaller tin-based perovskite grains with higher interfacial energy are preferred to dissolve in the liquid domain,while the larger tin-based perovskite grains with lower interfacial energy grow further with time.Therefore,benefiting from the BMIBr-induced Ostwald ripening effect,the high-quality tin-based perovskite films with larger grain size and fewer grain boundaries have been ultimately prepared,thus effectively improving the carrier mobility and optimizing the charge transport.Meanwhile,the significant reduction of the grain boundaries rich in defect states also shows that the erosion of water and oxygen can be effectively resisted,leading to the enhancement of device stability.Finally,the optimized tin-based PVSCs based on the BMIBr-induced Ostwald ripening effect has achieved an efficiency of 10.09%with significant enhancement in device stability,where aging in a nitrogen glovebox for 1200 h maintains almost 85%of initial PCE and aging in air for 48 hours keeps nearly 40%of initial PCE.