Study On The Perovskite Light-absorbing Layer And Electron Transport Layer In The Printable Mesoscopic Perovskite Solar Cells

During last decade,the certified efficiency of perovskite solar cells has rapidly increased to 25.2%,making perovskite solar cells a strong candidate for the next-generation cost-effective photovoltaic technology.Among various device structures,the printable mesoscopic perovskite solar cells(MPSC)based on the structure of mesoporous titanium dioxide layer/mesoporous zirconia layer/carbon electrode shows unique advantages in terms of low cost,good stability,and scalability.MPSC are considered to have great prospects for industrial application.However,MPSC face the problem of low power conversion efficiency(PCE).Since no hole transport layer is used in MPSC,the perovskite layer and porous electron transport layer(ETL)are the keys to improve the PCE.The filling of perovskite in thick porous films remains a problem,which directly limits the light absorption and the carrier transportation,and brings serious recombination losses.The widely used titanium dioxide ETL has problems of low mobility and strong photocatalytic activity.These problems restrict the device performance.This thesis focuses on the ETL and perovskite layer.The main contents are as follows:Fullerene derivative(PCBM)was introduced into perovskite as an additive.The PCE of MAPb I₃-based MPSC device was successfully improved from 8.58%to 12.36%,and the PCE of MAPb I_2.95(BF₄)_0.05-based MPSC device was improved from 12.77%to14.26%with the addition of PCBM.The PCBM additive significantly improves the morphology of perovskite film,and effectively promotes the separation of photogenerated charges and inhibit recombination of the MPSC devices.An in situ single crystal transfer method was developed based on gas-solid interaction,using methylamine gas to transfer MAPb I₃ single crystal powders to form high-quality crystals with small volume shrinkage in the triple-layer porous film,which effectively solved the filling problem of perovskite in MPSC.Benefiting from the effective pore filling and good crystallization of perovskite in the porous film,the PCE of MPSC device prepared by the in situ single crystal transfer method has been greatly improved to nearly 16%.Aiming at the problems of the ETL,barium stannate(BSO)nanoparticles were synthesized and mesoporous barium stannate was used as the electron transport layer in printable MPSC for the first time.Strontium solid solution barium stannate was further developed.The results show that the average open circuit voltage of the device increases as the content of strontium increases,but the short-circuit current density of the device tends to decrease.The optimal device performance is 9.23%when the strontium doping molar ratio is 0.15.The introduction of strontium upshifts the conduction band of barium stannate as well as its Fermi level,thus affecting the charge injection efficiency of the perovskite film.Then,the effect of lanthanum-doped BSO prepared in N₂ on the performance of printable MPSC was further explored.Studies have shown that as the doping amount of lanthanum increases,although the crystallinity gradually increases,the surface oxygen vacancy concentration in lanthanum-doped BSO gradually increases.And the lanthanum present on the surface of the material may become a recombination center,which causes the decline in various parameters of device performance.When the amount of lanthanum is less than 0.005,the peak efficiency of 12.11%is obtained.The effect of annealing atmosphere on BSO performance was explored,and a method for preparing BSO nanoparticles by annealing in nitrogen atmosphere and cooling in oxygen atmosphere was developed.BSO nanoparticles with high dispersibility and high crystallinity were successfully prepared.The surface and body oxygen vacancy concentrations of the prepared BSO nanoparticles were controlled to a certain extent.The PCE of the MPSC device based on the BSO electron transport layer reaches 14.77%.The PCE of the device keeps unchanged for 60 days in air.And it keeps unchanged for 34 h under 60 m W cm^-2 ultraviolet light soaking.