Research On Photoelectric Properties Of Perovskite Solar Cells Based On Polyoxometalate Componds Doped Hole Transport Layer

Perovskite solar cells(PSCs)have become a rising star in the photovoltaic industry nowadays,owing to the simple fabrication process and superior optoelectronic properties.Even though the impressive power conversion efficiency(PCE)of planer PSCs makes them promising candidate in commercial photovoltaic products,the major factors determining commercialization are shifting to the long-term operation stability and toxic lead-related environmental pollution issues.However,compared with the low efficiency and stability of lead-free perovskite photovoltaic devices,Pb and 2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenyl-amine)-9,9'-spirobifluorene(Spiro-OMe TAD)still are the indispensable components in the perovskite photovoltaic community.Aiming at the stability caused by the uncontrollable air oxidation process of Spiro-OMe TAD and lead pollution issues,this subject intends to design and synthesize the functionalized composite materials based on polyoxometalate(POM)and metal organic freamwork(MOF)as novel dopants for hole transport materials(HTM)system guided by energy level matching,achieving quantitative and controllable oxidation of Spiro-OMe TAD that is unaffected by the external environment such as air and minimization Pb lekage.In addition,the structure-activity relationship between the structure and PSCs'performance,charge transport kinetics and doping mechanism were explored.A POM-based compond[Cu(phen)₂]₂[(?-Mo₈O₂₆)](phen=1,10-phenanthroline)(POM-Cu-Phen)with strong electron-accepting properties was successfully synthesized and used as a novel dopant of HTM film for the first time.Under inert conditions,POM-Cu-Phen could replace the uncontrollable air oxidation process to achieve quantitative and controllable oxidation of Spiro-OMe TAD,which presents obviously increased conductivity and hole mobility in comparison to its counterpart.Effective charge extraction and transfer would inhibit the charge recombination between the perovskite and HTM interface.Compared with the counterpart(16.91%),the optimal concentration doped achieve a higher PCE of 18.72%,leading to a 10.7%PCE enhancement.Meanwhile,the introduction of conjugated organic ligands enhances the long-term stability of the device.Under the atmospheric environment for nearly one month,the PCE of PSCs based on POM-Cu-Phen still maintains about 85%of its initial PCE.To solve the problem of the aggregation of POM and the size of the material,the porous MOF with nanoscale could be applied to uniformly disperses POM molecules to construct compond:[Cu₂(BTC)_4/3(H₂O)₂]₆[H₃PMo₁₂O₄₀]₂(BTC=Trimesic acid)(POM@Cu-BTC).This type of material is used as a chemical dopant for HTM films for the first time.The H₃PMo₁₂O₄₀ molecule(Mo⁶⁺)can chemically oxidize Spiro-OMe TAD in an inert atmosphere,and the conductivity and hole mobility are increased by nearly two times.POM@Cu-BTC improves the efficiency of charge transfer and inhibits charge recombination.Combined with the continuously optimized preparation technology of PSCs,PSCs doped with POM@Cu-BTC exhibit the higher fill factor of 0.8,and the PCE is increased from20.21%for blank devices to 21.44%.More importantly,the porous structure of MOF can accommodate hygroscopic Li-TFSI,blocking its contact with water molecules.Therefore,the PCE retains approximately 90%of the initial value after long term storage in ambient environment without encapsulation,showing excellent stability.In view of the long-term stability and the environmental issues related to lead ions,a series of host-guest systems with MOF loaded POM:POM@MOF-545 were constructed,which combines the oxidation ability of POM and the stability of MOF-545.In an inert environment,the POM molecules in the composite material realize the controllable oxidation of Spiro-OMe TAD,and the oxidation capacity can be achieved by simply adjusting the loading of POM.The conductivity and hole mobility after POM@MOF-545 doping are twice as much as the blank HTM film.In addition,the porphyrin ligand in MOF-545 framework can passivate the perovskite interface in contact with the HTM film to make up the defects and improve the charges transfer efficiency as well as inhibit the charge recombination.The synergistic effect of POM and MOF improves the PCE(21.53%)and long-term stability(>1000 h)of PSCs.More importantly,the active sites in the system,such as the nitrogen atom of porphyrin and the terminal oxygen atom of POM molecule,endow POM@MOF-545 with excellent adsorption property,which can effectively capture Pb²⁺ions to minimize lead leakage and the impact on the environment.In this paper,the simple and effective chemical doping strategy was used to address the main commercialization challenges of PSCs,such as long-term operation stability and lead pollution.and prepare stable and environmentally friendly sustainable photovoltaics.These combined results provide a theoretical basis for yielding stable and environmental-friendly sustainable photovoltaic devices,which is of great significance to the industrial development of PSCs.