Preparation And Performance Research Of Perovskite Photovoltaic Devices Modified With Copper And Zinc Based Coordination Compounds

Photovoltaic devices based on organic lead halide perovskite materials have the advantages of facile preparation process and high efficiency.After just ten years of development,they have become one of the most competitive photovoltaic devices.At present,the state-of-the-art perovskite solar cells(PSCs)mainly compose of an electron transport layer,a perovskite light absorption layer,a hole transport layer(HTL)and a metal electrode.The most commonly used hole transport material is Spiro-OMeTAD,but its poor electrical properties cannot meet the carrier extraction and transport requirements of high-performance PSCs.Meanwhile,it has been easy to deposit smooth and dense perovskite films with good crystallinity,but there are still defects inside the films.Additive engineering is uaually utilized to regulate HTLs and perovskite layers,which not only helps further improve the power conversion efficiency(PCE),but also the long-term stability of PSCs.Therefore,we design and synthesize copper and zinc based metal-organic coordination compounds,which possess advantages of ease of synthesis,adjustable chemical components,and numerous active sites,to improve the functional layers of PSCs,thereby enhancing the overall performance of the devices.Through the reactions of Cu I and nitrogen-containing organic ligands,varieties of metal-organic coordination compounds with different structures and functions can be constructed.The copper coordination compound that matches the energy level of perovskite and Spiro-OMeTAD was screened.It was found that the nitrogen-containing heterocycles in the supramolecular framework of copper coordination compound could interact with Li-TFSI to promote the dispersion of lithium salt in the HTL.Thanks to the better dispersion of additives and the electronic transaction between Spiro-OMeTAD and the copper coordination compound,the electrical properties and morphology of the HTL were further optimized.Based on the HTLs modified by the copper coordination compound,high-performance PSCs were realized,and the highest PCE reached 18.47%,which was higher than that of the control(16.52%).The improvement was mainly due to faster hole extraction and transport,as well as suppressed carrier recombination at the interfaces.The hole transport layer modified by the copper coordination compound showed a larger water contact angle,and the cell modified with this additive could maintain more than 85%of the initial efficiency after 720 h of aging at ambient condition(25?,RH?30%).Two divalent copper based coordination compounds with different coordination forms were prepared by using different proportions of metal salts to react with flexible organic ligands containing nitrogen heterocycles and carboxyl groups.They were used to investigate the mechanism and influence factors of chemical p-doping Spiro-OMeTAD.It was found that the oxidation of Spiro-OMeTAD with solid additives needs Li-TFSI,which can accelerate the reaction process at the solid-liquid interfaces and stabilize the oxidation species.The oxidation level has a linear relationship with the concentration of Li-TFSI and copper based coordination compounds.Stable and controllable oxidation of Spiro-OMeTAD could be achieved through the coordination compounds under inert atmosphere,which can effectively improve electrical properties of the HTLs.Due to the better performance of the HTLs and the passivation of undercoordinated Pb²⁺on the surface of perovskite films,the highest PCE of PSCs prepared based on doped HTLs reached 20.97%,which was higher than that of the control oxidized in the air(19.88%).The hole transport layers doped with the copper coordination compound were more hydrophobic,which alleviated the change of film morphology and the decomposition of the perovskite layers.The corresponding device remained 84%of the initial efficiency after 720 h of aging at ambient condition(25?,RH?20%-40%).A novel zinc-based coordination compound was prerapred to investigate the grain boundary passivation of triple mixed cation perovskite films and the influence on stability of PSCs.Zinc-based coordination compound with the two-dimensional structure and numerous exposed active sites stably bonds with perovskite through coordination bonds and hydrogen bonds,so that it can tightly wrap the surface of Pb I₂-terminated perovskite grains,acting as the new terminated material.It can not only passivate the defects on the surfaces of perovskite grains,but also stabilize the crystal structure of the perovskite.In addition,the two-dimensional zinc-based coordination compound mainly distributing at the grain boundaries increases the adhesion of adjacent perovskite grains,avoiding the pinholes and cracks that may exist in the films.The perovskite films modified by the zinc coordination compound have lower defect state density,regular film morphology,and better optoelectronic performance.Therefore,the highest PCE of PSCs reached 21.28%,which was higher than that of the control(18.98%).The perovskite films modified with the zinc coordination compound show better structural stability and hydrophobicity,so the corresponding devices have better humidity stability and thermal stability.Stored in the surrounding environment(25?,RH?40%)for more than 1000 h,the device maintained 81%of the initial efficiency.After aging for 750 hours in a nitrogen atmosphere at 85?,the device maintained close to 90%of the initial efficiency.