| Organic-inorganic lead halide perovskite has become an ideal material for fabricating low-cost,easy-to-make and high-efficiency solar cells.Perovskite-based solar cells(PSCs)have achieved rapid progress in power conversion efficiency(PCE)over the past 12 years,increasing from 3.8%in 2009 to 25.5%in 2021,making them become one of the most commercially attractive solar cells recently.Among all PSCs,Organic-inorganic hybrid perovskite dominated by methylamine lead iodine perovskite(CH3NH3PbI3)possess highly potential as light absorbents.As is known to all,mesoporous-planar heterojunction structure has great advantages such as solving the problems of leakage or contact heterogeneity between mesoporous structure and planar structure,which is easy to make and beneficial for interface modification.Besides,carbon-based PSCs with hole-free transport layer possess broad prospects for commercialization due to the simple fabrication process and precious metals(such as Au and Ag)substitution for carbon(C),not only they reduce the costs,but also solve the problem of instability according to Spiro-OMeTAD and PTAA.However,the PCE of carbon-based PSCs is still relatively low.Importantly,regulating the light-absorbing layer is the key to improve the PCE,what's more,the defect passivation and interface modification are effective strategies.In this thesis,a PSCs of FTO/c-TiO2/m-TiO2/CH3NH3PbI3/C with mesoporous-planar heterojunction hybrid structure was fabricated,which adopated the basic structure of carbon-based HTM-free.In order to improve the PCE and environmental stability,the defects on grain boundaries and surface,or between the interface caused by fast crystallization should be passivated or interface modificated.The main researches are as follow:(1)The crystallization process of CH3NH3PbI3 light-absorbing layer was regulated by anion and cationic ligand.Guanidine thiocyanate(GUTS)with thiocyanate ions(SCN-)and guanidine salt ions(GUA+)were selected for thermal annealing treatment of CH3NH3I·PbI2·DMSO.Then,the effects of different concentrations of isopropanol solution(IPA)of GUTS on the properties of CH3NH3PbI3 films were studied.When CH3NH3PbI3 films were prepared by one-step anti-solvent method,the crystallinity of perovskite was improved due to Oswald curing between GUTS and CH3NH3I·PbI2·DMSO,and the corresponding grain size increase from 350 nm to 810 nm.The mechanism study shows that the anions and cations passivate the grain boundary and surface defects of perovskite together,and the synergistic effect can effectively inhibit the non-radiative recombination of carriers,reduce the density of defect states,and thus improve the carrier life of perovskite.In addition,the semiconductor properties of perovskite itself were optimized to narrow the band gap and increase the work function for the separation of light absorption layer carriers,thus greatly improving the current density of the PSCs.The average efficiency of the passivated device was improved after the device was assembled.The optimal concentration of GUTS was 5%M,the corresponding PCE was 12.47%,and the short-circuit current density was up to 22.62 mA/cm2.This study shows that appropriate passivation combined with energy level arrangement is an effective method to obtain efficient and stable PSCs.(2)The effects of different concentrations of butylamine iodide(BAI)on CH3NH3PbI3 thin films at different stages were studied by introducing shorter linear alkylamine functional groups to form multicomponent absorbents consisting of two dimensional and three dimensional(2D&3D)perovskites.After adding BAI in the middle phase of CH3NH3I·PbI2·DMSO.the humidity stability of the thin film is significantly improved,the interface is optimized.The presence of the 2D perovskite structure improves the energy level arrangement between perovskite and carbon electrode,thus ultimately increasing the open circuit voltage and filling factor of PSCs.It can be seen from the mechanism that 2D layered perovskite forms on the 3D perovskite with broadband gap due to the presence of n-butyl ammonium(BA+),further,carriers continue to transmitted in the grain instead of recombination because of the 2D to 3D heterojunction barrier.It can effectively reduce the defects density of states,and improve the carrier lifetime of perovskite.In addition,the optimized composition of the 2D-3D perovskite heterojunction can significantly improve the charge transfer performance,further inhibit the ion defects at the interface,and expand the fermi level splitting to reduce the band gap voltage loss.On the other hand,the overall efficiency of the perovskite cell treated with BAI was improved,and the optimal concentration of BAI was 15 mM,corresponding to the PCE of 12.61%,the open circuit voltage of 0.961 V and the fill factor of 63.69%.In addition,the BAI treated devices retained 84%of their initial PCE when stored at 30±5%RH for 32 days.(3)The crystallization process of perovskite absorption layer was controlled by the combination of the defect passivation of anionic and cationic ligands and the interface engineering with shorter linear alkylamine functional groups.The effects of the interaction of the optimal concentration of GUTS and different concentrations of BAI on the properties of CH3NH3PbI3 films were studied.It shows that the PbI2 precipitates were extracted at the perovskite grain boundary after the passivation of GUTS.so the 2D structures can be formed by adding BAI,even after the formation of the final phase of CH3NH3PbI3.In this way,the PCE has been greatly improved by combining the characteristics of high short-circuit current of GUTS and high open circuit voltage of BAI.which achieve the best PCE performance of 12.61%,corresponding to the short circuit current density of 21.14 mA/cm2,the open circuit voltage of 0.979 V,and fill factor of 62.38%.Moreover,the optimal device concentration was 5%M GUTS and 5 mM BAI,the study provides a new strategy for the construction of stable mesoporous-planar 2D-3D heterojunction hybrid PSCs. |
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