Application Of Small Molecule Hole Transport Materials Based On The Core Of Azulene In Perovskite Solar Cells

In recent years,perovskite materials have been widely studied by researchers because of their excellent photoelectric properties.At the same time,perovskite solar cells(PSC)have been developing rapidly with the advantages of excellent power conversion efficiency(PCE)and simple preparation process.As one of the key components of PSC,the hole transport layer has the functions of extracting holes and inhibiting carrier recombination.At present,2,2’,7,7’-Tetrakis-(N,N-di-4-methoxyphenylamino)-9,9’-spirobifluorene(Spiro-OMeTAD)is commonly used as the hole transport material for the formal structure(n-i-p)PSC,and the highest certification efficiency has reached 25.8%.However,due to the cumbersome synthesis route and high purification cost,Spiro-OMeTAD cannot be widely applied,which greatly limits the commercialization of perovskite solar cells.In order to solve the above problems,researchers are focusing on the design and synthesis of new low-cost,high stability hole transport materials to replace the traditional Spiro-OMeTAD,and promote the commercialization of batteries.In this paper,a series of low-cost hole transport materials are developed by means of molecular engineering,which can be used to construct efficient and stable perovskite solar cells.A series of organic small molecule hole transport materials based on azulene were synthesized by carefully adjusting the core structure and peripheral groups of the hole transport material,and the effects of different peripheral group hole transport materials on the photoelectric properties of PSC were systematically studied.The specific research is as follows:1.Two hole transport materials with azulene as the core and thiophene as the bridge are designed and synthesized.Two new hole transport materials Azu-THCZ and Azu-THDF are prepared by introducing carzole and azulene to the periphery to control energy levels.It was found that due to the strong power supply of thiophene groups,the material would have a relatively shallow HOMO level,in which the HOMO level of Azu-THCZ with carbazole was-4.7ev,the perovskite valence band was not matched,and the hole transport efficiency was not ideal.Fluorene introduced by Azu-THDF expands the conjugation degree of molecular groups and improves the efficiency of hole transport.2.On the basis of work 1,the molecular structure of the hole transport material is further optimized to achieve the matching of energy levels.Two hole transport materials Azu-TPA and Azu-OMeTPA are obtained by substituting phenyl for thiophene bridging groups.Both AzuTPA and Azu-OMeTPA are well matched with perovskite energy levels,and have high hole mobility and conductivity.In addition,this kind of hole transport material has good hydrophobicity,which can improve the stability of the device to a certain extent.However,due to its low solubility,the film forming property of hole transport material is poor and the coverage degree is low,which reduces the extraction and transportation efficiency of holes.Among them,the Azu-OMeTPA device obtains 15.41% PCE.3.On the basis of azulene,the material is further modified.Azu-Py-DF and Azu-PyOMeTPA materials matching the energy level of perovskite are obtained by using azulene as the core and introducing pyridine group on the 6 sites of azulene.The different spatial orientation of pyridine and Azulene cores improves the solubility of the material and helps to improve the film form.Moreover,pyridine can passivate the surface defects of perovskite,which improves the efficiency and stability of solar cell devices.When Azu-Py-OMeTPA is applied to the device,the efficiency of 18.10% is obtained.