Molecular Engineering Of Carbazole-bazed Dopant-free Hole Transport Materials And Its Applications In Perovskite Solar Cells

Due to its remarkable advantages in cost and efficiency,perovskite solar cells（PSCs）have become competing research hotspots for photovoltaic field.Though the current power conversion efficiency（PCE）of PSCs is striking above 25%,meeting the requirements of commercial applications,its long-term stability,environmental protection and large-area module technology issues are still pending.Wherein,part of the reason for the poor long-term stability is the inclusion of necessary hygroscopic dopants in hole transporting materials（HTMs）in high-performance PSCs devices,and the introduction of hygroscopic dopants accelerates the degradation of perovskite.Hence,the design and development of high-efficient dopant-free HTMs evolves as an effective approach to improve stability of PSCs.Compared with polymer-based dopant-free HTMs,small molecule HTMs have promising application potential due to the advantages of well-defined molecular structures,high batch-to-batch stability,facile synthesis,and low-cost.Based on this,a series of novel carbazole-based organic small molecule dopant-free HTMs were designed and synthesized by modulating the core conformation,peripheral substituents and connection methods in this thesis,and the physicochemical properties,hole transport properties,and the impact on the photovoltaic performance and stability in PSCs of the newly developed HTMs were investigated in detail.The main research contents are described as follows:（1）With the strategy of tuning the molecular core planarization,the dimer carbazole ring-fused core was innovatively prepared by metal-free catalysis,and 4,4’-dimethoxydiphenylamine was introduced as peripheral group to design and synthesize the organic small molecule material NCz-DM with D-π-D structure.It was found that the novel dimer carbazole ring-fused core was constructed to effectively improve the intermolecularπ-πstacking,enabling the dopant-free HTM NCz-DM(9.41×10^-4 cm²·V^-1·S^-1)to perform better hole mobility than the doped Spiro-OMe TAD(6.82×10^-4 cm²·V^-1·S^-1).A PCE of 18.19%was obtained by employing dopant-free NCz-DM in organic-inorganic hybrid lead-based PSCs,and the stability of the devices was remarkably improved.（2）With the strategy of molecular peripheral electric-supplied modulation,the dimer-type carbazole-based organic small molecule materials DF and TF with deep energy levels,excellent charge transmission performance and good hydrophobicity were designed and developed.It was found that the material TF could be combined with Spiro-OMe TAD to construct double organic hole transport layer with gradient energy level arrangement and employed in lead-free Cs₂Ag Bi Br₆ PSCs,which can effectively reduce the energy loss owing to the valence band offset between Cs₂Ag Bi Br₆ and the hole transport layer.Through optimization,a PCE of 3.50%is finally achieved,and the stability of the devices were greatly improved.（3）Using benzene as theπ-bridge,by the strategy of adjusting the position of the conjugate bridge connected to the peripheral groups,dimeric carbazole-based organic small molecule materials o-PCz,m-PCz and p-PCz with different degrees of twisting were designed and developed.It was found that p-PCz with slightly twisted backbone showed quantum increases in hole mobility compared to o-PCz and m-PCz with strongly twisted backbone.Futhermore,the p-PCz material exhibited excellent film-forming properties with the combination of dynamic spin-coating method and non-halogenated solvent THF.The Cs₂Ag Bi Br₆ based devices with dopant-free HTM p-PCz obtained a PCE of 2.44%,and the stability of the devices were improved.