The Structure Design And Synthesis Of Dopant-free Organic Hole Transport Materials And Their Performance Characterization

The perovskite absorbing layer has the advantages of adjustable absorbent layer band gap,low exciton binding energy,high carrier mobility,simple device structure,low-cost and high efficiency power efficiencies make it become research hotspot.Now the device based on Spiro-OMe TAD produced highest PCE,the application of the Spiro-OMe TAD as HTM in PSCs requires metal complexes and additives.In spite of the improvement in conductivity,the use of these dopants not only complicates the device fabrication but also poses threats on the stability of the resulting PSCs.This paper aims to study the effects of different donor and acceptor structures and different carbon-carbon bond connections on the photoelectric physical and chemical properties of hole transport materials,meanwhile providing the idea and reference for the design of the synthesis and efficient hole transport materials.Our main research is as follows:(1)Three small hole transport materials based on triphenylamine as a donor and PTZ was the core unit of D-?-D structure were designed and synthesized.The solubility in organic solvents and photovoltaic properties of the alkyl chain control material by changing the length of alkyl chain connected on the PTZ nitrogen atom.It is found that the contorted triphenylamine and PTZ formed the non-planar structure by C-C bond which can regulate molecular aggregation behavior and the length of the alkyl chain which can regulate the film-forming and hydrophobic properties on the absorbent layer,and ultimately affect the photovoltaic properties of the device.By gaussian calculation of the density functional theory(DFT),it was found that the suitable energy level difference between the material and the perovskite absorber layer was conducive to obtaining a high open circuit voltage.Changing the length of the hydrophobic chain and introducing alkyl bromine atoms have an effect on the distribution of the electronic cloud density of the molecule,and cycle voltammograms(CVs)had the same trend as the energy level calculated by the DFT.The space charge limited current test(SCLC)found that the performance of the three HTM was not ideal,and the HTM with hexyl chain had a poor hole mobility without doping far less than the other two materials,resulting in a PCE of only 6.87 %.The distorted molecular structure of triphenylamine and the phenothiazine(PTZ)molecule cannot improve the hole mobility of the molecule and the molecular structure cannot satisfy design requirements of highefficiency HTM,which provides the reference basis for the design and development of the new hole transport materials structure.(2)Two small molecular HTMs with strong electron donating carbazole as donor the acceptor of PTZ and POZ were designed and synthesized.The hexyl chain connecting the hydrophobic D-unit with the PTZ and POZ donor units can form a crossstereoscopic non-planar molecular structure and the carbazole molecule has the advantages of simple synthesis step and high yield.It can be seen from the front-line orbit map that the molecular structure of the KZ-PTZ and KZ-POZ has a suitable energy level difference with the perovskite absorbent layer,which is conducive to obtaining a higher open circuit voltage.However,the electronic cloud density does not be uniform distribution in the whole molecule,which will affect hole mobility of the molecule.By testing the single crystal structure formed,it is found that the interaction distance between molecules is far from the order of accumulation,thus proved a cross-dimensional structure is not feasible from the molecular level.When the HTM is applied to the structure of formal devices,it is found that due to poor-quality HTM film performance and serious recombination losses,the PSCs fabricated with the n-i-p architecture using KZ-PTZ and KZ-POZ as the dopant-free HTM achieve the device efficiency is only 3.72% and 4.08%.(3)Based on the previous two types of molecular design and inspired by the previous research group,this chapter designed and synthesized two types of Benzo[1,2-b:4,5-b?]dithiophene-4,8-di(hexylthiofos)(BDT)as the core,PTZ and POZ as donor,and through a single,double-bond to form a D-?-D organic molecule with an approximate planar structure.First of all,by comparing Suzuki coupling synthesis of two HTM BDT-PTZ,BDTO-PTZ,it is found that BDT-PTZ has a deeper HOMO energy level that has more suitable energy level match with perovskite absorbent layer can contribute to the improvement of open-circuit voltage.At the same time,atomic force microscope(AFM)test found that BDT-PTZ has smaller roughness and fewer defects when using the molecule as HTM are contributed to the formation of the homogenous film.Secondly,it explores the effect of the molecular conformation by means of two-bond connection between molecules,and the target molecule QSN01,QSN02 is synthesized by Witting coupling,the DFT calculation is carried out on it.The distribution of electron clouds in molecules is simulated by Gaussian calculation,and a good energy level match is found between it and the perovskite absorbent layer.In addition,the NMR the molecular structure is further determined.