Synthesis And Photovoltaic Properties Of Dopant-Free Hole-Transporting Materials Containing Conjugate Plane Cores

Perovskite solar cells?PSCs?are a new type of solar cells based on dye-sensitized solar cells.They have aroused significant attention due to their low-cost fabrication process,strong light capture capability and excellent photovoltaic performance.Hole-transporting materials?HTM?contacts with the perovskite active layer directly,which constitutes important functional layer of PSCs,as it efficiently facilitates the photo-induced hole extract and transfer from perovskite toward the electrode and suppresses the charge recombination,and also act as a perovskite surface barrier to against moisture and oxygen intrusion.Among them,organic small molecule HTM has attracted much attention due to its many advantages such as lower cost,good solubility,and easy modification of chemical structure.In most cases,organic small molecule HTM needs chemical doping to improve its hole mobility,but chemical dopants have a large negative effect on the stability of PSCs.At present,studies have shown that the core of small organic molecule HTM will affect the?-?stacking between molecules,and the rigid large conjugated fused-core can promote the?-?stacking between molecules and significantly improve hole mobility of the HTM.Therefore,it is very important to find large conjugated fused rings to construct dopant-free organic small molecule HTMs.In this thesis,seven hole-transporting material molecules containing star-shaped imidazole-based and linear-shaped indole-based were designed and synthesized.The relationship between material properties and molecular structure was studied by measuring their photophysical,electrochemical,thermal stability,etc.The star-shaped imidazole-based material molecules were applied to PSCs,and the relationship between molecular structure and performance was studied through the photoelectric performance of PSCs.The specific research work is summarized as follows:?1?The second chapter innovatively introduces conjugated fused ring dithieno[3',2':3,4;2'',3'':5,6]benzo[1,2-d]imidazole?DTBI?and phenanthro[9,10-d]imidazole?PTI?as the core group in the HTMs.Different steric group?4-methoxybenzene and4,4'-dimethoxytriphenylamine?are introduced as the periphery groups connected at imidazole moiety carbon-2 position.Three novel imidazole-based HTMs?namely M1,M2,and M3?with 4,4'-dimethoxytriphenylamine as the donors were synthesized,and characterized by¹HNMR,¹³CNMR and HRMS.Photophysical and electrochemical experiments show that the donors and the cores of M1-3 determine the HOMO and LUMO levels,respectively,and their energy levels can be well matched.Thermogravimetric analysis?TGA?and differential scanning calorimetry?DSC?show that M1-3 both have good thermal stability,and M2 has the best stability in the amorphous state.The hole mobility experiment obtained hole mobilities of M1-3,and M1-2 had higher mobility.The dopant-free M1-3 were applied to the PSCs with a structure of ITO/Sn O₂/FA_0.85MA_0.15Pb Br_0.45I_2.55/HTM/Au,and M2-based PSCs achieves the best photovoltaic performance with a power conversion efficiency?PCE?of16.90%,outperforming that of the devices using doped spiro-OMe TAD as HTM?16.35%?under the same testing conditions.In addition,the devices based on DTBI-cored M1 also achieved a satisfactory PCE of 16.14%.However,the PTI-cored M3 show an especially low PCE of 7.33%once applied to the PSCs as dopant-free HTM.It shows that the core structure has a decisive influence on the performance of the HTMs.In addition,the fused DTBI is a potential building block for dopant-free HTM in efficient PSCs.?2?The third chapter,four novel indole-based HTMs?D1-4?were synthesized,where conjugated fused-ring indolo[3,2-b]indole?IDID?was introduced as the core,and1,4-dimethoxytriphenylamine as the donor.The?-conjugation of D2-4 is extended by different linking bridges?benzene,thiophene,and benzothiadiazole,respectively?.The effect of the linking bridge on material properties and photovoltaic performance of the HTMs was studied.The molecular structures of D1-4 were characterized and confirmed by ¹HNMR,¹³CNMR and HRMS.Photophysical and electrochemical experiments show that D1-4 both have theoretically matched energy levels.Thermogravimetric analysis and differential scanning calorimetry determined the thermal decomposition temperature and glass transition temperature of D1-4,and the thermal stability can meet the requirements.The design and synthesis of four linear-shaped conjugated molecules is aimed at finding excellent dopant-free HTMs and contributing to the development of perovskite solar cells.