Preparation Of High-efficiency Quasi-two-dimensional Perovskite Solar Cells Based On GA₂MA₄Pb₅I₁₆

The efficiency of 3D perovskite solar cells has increased from 3.8% to 25.7% in the past 10 years,showing great development prospects.However,stability has hindered the commercialization of 3D perovskite solar cells.Quasi-2D-Ruddlesden-Popper（2D-RP）perovskite has been widely welcomed by researchers because of its excellent stability.However,the efficiency of 2D-RP perovskite solar cells is still far behind from that of 3D perovskite solar cells,one of the main reasons is that it is relatively difficult to prepare high-quality 2D-RP perovskite thin films.Two aspects are discussed in this paper,that is,optimizing the preparation process and incorporating additives,to prepare high-quality 2D-RP perovskite films,so as to improve the efficiency of 2D-RP perovskite solar cells.The main contents of this paper are as follows:（1）Optimizing the traditional one-step preparation process.The effects of different antisolvents on the properties of GA2MA4Pb5I16 thin films and their devices were systematically investigated.Firstly,the effects of three antisolvents,namely toluene（TL）,ethyl acetate（EA）and chlorobenzene（CB）were studied on the performance of GA2MA4Pb5I16-based solar cells.It is indicated in the J-V test results that the device prepared with CB antisolvent treatment shows the best efficiency,with the optimal device efficiency up to 13.33%,and the hysteresis effect of the device is improved in a rather obvious manner,where the hysteresis index（HI）of the device with CB treatment is reduced to 0.06,while the HI of the device with TL and EA treatment are 0.31 and 0.23 respectively.The stability test shows that the device with CB treatment shows excellent stability,where it still keeps 85% of the initial efficiency after being placed in air with 30%relative humidity（25°C）for 30 days.Finally,the study was also performed on the effect of the above three antisolvents on the properties of GA2MA4Pb5I16 thin films.According to the characterization analysis with scanning electron microscopy（SEM）,atomic force microscopy（AFM）and X-ray diffraction（XRD）,CB antisolvent can significantly improve the crystallinity of the films and reduce the surface roughness of the films compared with the other two antisolvents.This is because CB is not volatile,has a higher boiling point and can be well miscible with DMF/DMSO.According to the characterization analysis of Steadystate fluorescence（PL）and transient fluorescence（TRPL）,CB as antisolvent can effectively reduce the density of defect states on the film surface and prolong the lifetime of the charge carriers（72.1 ns）.（2）Employing the scheme of adding additive.On the basis of the previous work,Methoxyammonium Salt（Me O）is added into perovskite precursor solution to further improve the quality of GA2MA4Pb5I16 thin films,so as to improve the device efficiency.Me O can enhance the interaction between adducts of Pb I2-DMSO,so as to delay the transformation from Pb I2-DMSO to perovskite during annealing,thus is helpful to the formation of large perovskite grains.Firstly,the impact of Me O concentration on the GA2MA4Pb5I16-based solar cells performance was studied.According to the J-V test,the performance of the device reaches the best when the concentration of Me O is 1 mg/m L,with the efficiency of the optimized device up to 14.94%,which is 11.6% higher than that of the control device（13.39%）,and the steady-state output efficiency of the optimized device within 300 s reaches 14.73%.The stability test shows that the optimized device still maintains 89% of the initial efficiency after being placed in air with 30% relative humidity（25°C）for 720 hours,while the efficiency of the control device decays to82% of the initial efficiency under the same condition.Secondly,the impact of Me O concentration on the properties of thin films was studied.According to the characterization analysis with SEM and AFM,When the concentration of Me O is 1 mg/m L,the grain size of perovskite increases significantly,and the average grain diameter reaches 252 nm,which is 55.55% higher than that of pure perovskite（162 nm）,meanwhile the film roughness is also improved.When the Me O concentration increased to 1.5 mg/m L,the film quality decreased.Finally,the films were characterized in depth at the optimal Me O concentration.According to the characterization analysis with XRD and UV-vis,Me O can improve the crystallinity and light absorption of the films,and the films before and after optimization show similar XRD spectra,indicating that Me O does not enter the perovskite,but volatilizes during annealing.According to the characterization analysis of PL,TRPL,Ideal Factor and SCLC,Me O can significantly reduce the density of defect states on the surface of the thin films and inhibit the recombination of charge carriers,and the density of defect states on the surface of the thin films decreases from 2.92×1017cm^-3 to 2.44×1017cm^-3 after optimization.