Synthesis Of Asymmetric Triarylamine Electron-donating Groups And Their Applications For Hole-transporting Materials

Perovskite solar cells(PSCs)have received more and more attention in the photovoltaic field in recent years due to their high photoelectric conversion efficiency(PCE)and relatively simple preparation process.As an important part of the perovskite solar cell,the hole transport layer is mainly responsible for the extraction and transport of holes.Spiro-OMe TAD which is mostly used as hole-transporting materials(HTMs)in n-i-p structure PSCs has been extensively studied.However,its high price and inherent molecular defects hinder the commercialization of PSCs.Therefore,it has become a goal to search cheap and efficient HTMs which can replace Spiro-OMe TAD.At present,most of the new HTMs use methoxy-substituted triphenylamine to connect to different central cores.The main research work focuses on the development of different types of cores,while ignoring the research on the peripheral triarylamine.Therefore,the design and synthesis of new triarylamines is important for obtaining efficient and stable HTMs and preparing efficient and stable PSC.In this work,we introduced dimethyl fluorene,spiro[fluorene-9,9'-xanthene](SFX),indeno[1,2-b]thiophene,benzo[b]thieno[2,3-d]thiophene and indeno[1,2-b]thieno[2,3-d]thiophene into triphenylamine to construct five asymmetric triarylamines.Then 3,4-ethylenedioxythiophene(EDOT)is connected with different peripheral groups to obtain compound Z09-13,and dithienopyrrole(DTP)is combined with different triarylamines to obtain Z04-05.Studies have shown that the introduction of these groups improves the photoelectric properties of triarylamine and improves the stability of the hole transport layer.Photophysical and electrochemical measurements show that adjusting the substituents on the triarylamine has a greater impact on the HOMO energy level of HTMs.Thermogravimetric and differential thermal analysis show that both Z09-13 and Z04-05 have good thermal stability.Hole mobility and electrical conductivity tests show that holes Z13 and Z05 have higher hole transport and conductivity.Applying Z09-13 and Z04-05 to PSCs devices with ITO/Sn O₂/Perovskite/HTM/Au structure,the PCE of the Z13-based device can reach 18.21%,and the PCE of the Z05-based device obtains a satisfactory PCE of 20.72%,exceeding Spiro-OMe TAD(19.84%)under the same conditions.We tested their steady-state photoluminescence(PL),time-resolved transient photoluminescence fluorescence spectroscopy(TRPL),open-circuit voltage decay(OCVD)and impedance.The results show that Z05 has the best hole extraction and the smallest charge recombination at the PVSK/HTL interface.AFM,SEM and water contact angle tests show that Z05 has excellent film-forming properties and hydrophobicity.PSCs based on Z05 can still maintain more than 80%of the initial efficiency after 1000 hours of storage in an unencapsulated condition.The above work shows that using asymmetric triarylamine to construct HTMs is an effective strategy to improve the performance of HTMs.By adjusting the three substituents on the triarylamine nitrogen,the performance of HTMs can be controlled.This work provides experimental and theoretical basis for designing efficient and stable HTMs.