Design Of Fluorene Derivative Hole Transport Materials And Their Application In Perovskite Solar Cells

In the context of advocating low-carbon life,it is necessary to improve the utilization rate of clean energy such as solar energy.As one of the technologies of optical conversion,photovoltaic power generation has also received widespread attention.Since 2009,halide perovskites have been used as light-absorbing materials for solar cells.Significant progress has been made on perovskite solar cells(PSCs)in crystal structure,operation mechanism,and performance optimization.Perovskite can be prepared from cheap solvent processing technology,especially suitable for photovoltaic devices.As an important part of the structure of PSCs,the hole transport layer(HTL)needs to have high hole extraction ability.However,the hole transport ability of traditional hole transport materials(HTMs)2,2’,7,7’-tetra[N,N-bis(4-methoxyphenyl)amino]-9,9’-spirobifluorene(Spiro)is not ideal,and it is usually necessary to use additives.However,the presence of additives will decrease the chemical stability of the device.Therefore,researchers have focused on low-cost organic small molecule HTMs,which is easy to be synthesizedof.In this dissertation,a series of organic small molecule HTMs with fluorene derivatives as the core and methoxytriphenylamine as the terminal group were designed and synthesized.The effects of physical and chemical properties and structural characteristics of materials on the photoelectric properties of PSCs.The main work of this dissertation is as follows:1.A hybrid multi-site synergistic passivation strategy was proposed and successfully applied to PSCs.A novel HTM coded as TPA-DN was synthesized by introducing a nitrogen heteroatom on the core of the conjugated functional group 9-fluorenone.The theoretical calculation based on density functional theory,13C NMR,FTIR and XPS are used to explore the mechanism of mixed multi-site synergistic passivation.It is found that the introduction of nitrogen heteroatoms can increase the density of carbonyl electron cloud,thereby enhancing the passivation effect of carbonyl on uncoordinated divalent lead ions in perovskite.Moreover,the nitrogen atom can also act as a Lewis base to chelate with uncoordinated lead ions.Multiple passivation sites cooperate with each other to optimize the molecular structure,reduce the interface trap state and optimize the device performance.Compared with TPA-9O,the hole mobility based on TPA-DN material increases by 71%,and the trap state density of the device decreased by 49%.The introduction of nitrogen atoms improves the energy level and stability toward heat stress and moisture,and the power conversion efficiency(PCE)of the device is also increased from 18.37%to 19.45%.2.The HTM(TPA-DCN)with local near-infrared aggregation-induced emission characteristics was synthesized.Using DFT and MS theoretical calculations,TPA-DCN in the aggregated state has a smaller intramolecular rotation angle,a smaller charge recombination energy,and a smaller energy change generated by charge transport.The intramolecular charge transfer amount calculated by the interfragment charge transfer method(IFCT)is greater than 1,and the intramolecular Coulomb attraction is weak when the charge is transferred,which is very conducive to charge transfer.Therefore,TPA-DCN has high hole-transport efficiency.The hole mobility of TPA-DCN is 9.96 × 10-4 cm2 V-1 s-1,which is nearly two orders of magnitude higher than that of Spiro.Through XPS,FTIR,Raman,and XRD,it is proved that the cyano group in TPA-DCN acts as a Lewis base to provide electrons to the uncoordinated lead ions in the perovskite layer,which has a strong defect passivation effect and reduces the non-radiative recombination of carriers at the interface between the photosensitive layer and HTL.Compared with Spiro,PSCs based on TPA-DCN obtains a PCE of 20.27%,and showes better Jsc,Voc and FF.