Research On Dion-Jacobson Phase 2D Lead-based Perovskite Solar Cells

Three-dimensional（3D）metal halide perovskites show great potential for application in solar cells due to advantages of high absorption coefficient,long charge diffusion length,excellent carrier mobility,and tunable bandgap.At present,the power conversion efficiency（PCE）of perovskite solar cells（PSCs）has grown rapidly to 25.7%,whose efficiency has met the needs of commercialization,but the stability of 3D PSCs limits its future commercialization to a certain extent.A series of strategies such as doping,component engineering,interfacial modification,use of novel electron and hole transport materials and encapsulation have been used to improve the stability of PSCs.Recent studies have shown that reducing the dimension of perovskite to prepare two-dimensional（2D）perovskite,which can effectively slow down the oxidation of the perovskite film and greatly improve the device stability.The improvement of its stability is mainly due to the lower ion mobility and a hydrophobic sandwich structure.The thesis mainly focuses on the preparation of Dion-Jacobson（DJ）phase 2D layered perovskite films and deviece with more stable structure and better electrical conductivity to improve the stability of PSCs,which is mainly consist of the following three parts:（1）1,4-cyclohexanebis（methylamine）（CAM）that was selected as the spacer of 2D perovskite（CAM）MA₄Pb₅I₁₆（n=5）was proved to form a DJ phase 2D perovskite and its improved effect on film and device stability was also explored.The characterizations on photoluminescence（PL）spectra,ultraviolet-visible（UV-vis）absorption spectra and X-ray diffraction（XRD）figure demonstrated the successful preparation of the DJ phase 2D layered perovskite.Furthermore,the layer number of（n=1～5）and the solvent system were optimized,and it was found that when the number of layers n was5 and the mixed solvent ratio of DMF:DMSO was 7:3,the device performance was the best and the PCE reached 7.31%.The stability tests of the films and devices showed that the DJ phase 2D layered perovskite films did not decompose when they were located in air（RH=70±5%,T=85 ^oC）for 10days.Only the intensity of the～14°and～28°peak in XRD was slightly reduced,and the stability was much better than that of the 3D perovskite films that decomposed within one day.The efficiency still maintained 95%of its initial efficiency after 45 days of storage in N₂ atmosphere（T=25 ^oC）,while3D PSCs only maintained 62%of their initial efficiency.The above results show that the DJ phase2D layered perovskites prepared in this thesis have excellent stability.（2）4-aminobenzylamine（4ABA）that was chosen as the spacer of（4ABA）MA₃Pb₄I₁₃（n=4）was proved to form a 2D DJ phase perovskite and its improved effect on film and device stability was also explored.Compared with low dielectric constant and insulation property of the aliphatic diamine CAM in the above work,the aromatic spacer hasπelectron delocalization and larger dielectric constant.It can reduce the dielectric mismatch between the organic layer and the adjacent corner-shared[Pb I₆]^4-inorganic layer and weaken the dielectric confinement effect in the quantum well,while theπelectron delocalized structure facilitates the transport of charges.so 4ABA was selected in this part as a spacer for DJ phase 2D layered perovskites.In addition,πelectron delocalization structure also benefits charge transport within perovskite films.The characterizations on PL spectra,UV-vis absorption spectra and XRD figure demonstrated the successful preparation of the（4ABA）Pb I₄ DJ phase 2D layered structure.Furthermore,the number of perovskite layers（n=1～5）was optimized,and it was found that when the number of layers was n=4,the device performance was the best and the PCE could reach 9.61%.The DJ phase 2D layered perovskite films were partially decomposed into components with low n values and the peak intensity～14°and～28°decreased slightly when exposed to high temperature and high humidity（RH=70±5%,T=85 ^oC）in air for 10days.The stability was much better than that of the 3D perovskite films which decomposed within 7days.The efficiency still maintained 78%of its initial efficiency after 60 days of storage in N₂atmosphere（T=25 ^oC）while the 3D perovskite cells dropped to 40%of the initial value within 20days.（3）3-aminobenzylamine（3ABA）was also selected as the spacer of（3ABA）MA₃Pb₄I₁₃（n=4）,and a DJ phase 2D perovskite with 3ABA was formed.The difference between 3ABA and 4ABA spacers and their influence on the film and device stability was explored in this part.The symmetric structure of 4ABA²⁺used in the previous chapter keeps the DJ phase structure undisturbed,while the perovskite crystal structure composed of 3ABA²⁺is slightly shifted,and the reduced octahedral twist results in a smaller band gap of（3ABA）MA₃Pb₄I₁₃ 2D layered perovskite than（4ABA）MA₃Pb₄I₁₃perovskite.The 3ABA²⁺spacer distance in（3ABA）MA₃Pb₄I₁₃perovskite slightly smaller than that in（4ABA）MA₃Pb₄I₁₃one,Thus it is beneficial to carrier transport in（3ABA）MA₃Pb₄I₁₃perovskite.The resulting PSCs using（3ABA）MA₃Pb₄I₁₃as the light absorbing layer performed excellently with a PCE of 12.04%.The stability test of both the perovskite film and the device showed that the DJ phase2D layered perovskite films were partially decomposed into components with low-n components at10 days,and the peak intensity at～14°and～28°reduced slightly when they were exposed to high temperature and high humidity（RH=70±5%,T=85 ^oC）in air for 10 days.The efficiency still maintained 93%of its initial efficiency after 64 days of storage in N₂ atmosphere（T=25 ^oC）,much higher than 4ABA n=4 device stability,showing excellent stability.