Theoretical Study On Three Aromatic Derivative Of High Performance Hole Transporting Materials

In recent years,perovskite solar cells?PSCs?have attracted great attention due to the rapid rising photoelectric conversion efficiency?PCE?.At the same time,the hole transport layer has also become a research focus because of its special role in PSCs.A series of small-molecule organic hole transport materials?HTMs?were designed to explore electrochemical properties by density functional theory?DFT?and the first-principle calculations combined with Marcus theory.Several promising novel HTMs were predicted and expected to show a higher PCE.The main contents is listed in this paper as follows:?1?Several carbazole derivatives?V866,V867 and V868?as hole transporting materials?HTMs?in perovskite solar cells are designed to explore the functional group position effect on electrochemical properties.The results illustrate that V866?ortho-position?has the suitable HOMO energy level matched with the metal electrode?-5.1 eV?and the perovskite absorption layer?-5.4 eV?.Moreover,the molecular planarity of HTMs with the ortho-position functional groups is improved,which enhances intermolecular face-to-face?-?stacking degree.Compared to V867 and V868,the largest hole mobility value(0.007 cm² V^-11 s^-1)of V866 is obtained due to its modified molecular planarity.Therefore,V866?ortho-position?is indeed an excellent carbazole HTM.?2?We present a theoretical investigation of thiophene substituent effects on the electrochemical properties of dipolar chromophores?TCNE,TCNE22 and TCNE24?as hole-transporting materials?HTMs?in perovskite solar cells?PSCs?.The results show that the increased number of thiophene substituents for TCNE,TCNE22 and TCNE24result in a red shift of the absorption spectrum?27⁴6 nm?.Furthermore,both TCNE22and TCNE24 have maximum absorption peaks at a wavelength of 400 nm.Most importantly,the molecular planarity is improved effectively,which generates strong intermolecular face-to-face?-?packing interaction.The higher hole mobility of TCNE24(2.069×10^-1cm²V^-1s^-1)with four thiophene substituents is obtained due to the face-to-face?-?packing.The new designed TCNE24 not only has excellent spectral property,but also has strong hole mobility.Therefore,TCNE24 is a promising organic small-molecule HTMs.?3?In this paper,a series of carbazole derivatives?spiro-OMeTAD,V861 and V862?applied to the experiment as HTMs in PSCs is systematically studied on the electrochemical properties in theory.The material properties are explored by using DFT and the first-principle calculations combined with Marcus theory.The results show that the introduction of the conjugate core and the increase of the conjugate length for carbazole derivatives not only improve material absorption spectral properties,but also effectively increase material hole mobility under the condition that can match the molecular orbital energy levels of perovskite absorption layer and the metal electrode.In order to verify the universality of this conclusion,V863 and V864 are designed by by the introduction of PhTT and s-DTT.The results displays that under the premise of matching molecular orbital energy levels,the hole mobility shows a trend of increasing firstly and then decreasing.Meanwhile,V863 with the best conjugation length possesses the largest hole mobility.In conclusion,V863 possess suitable molecular orbital energy levels,wide UV-Vis absorption range and the largest hole mobility.Therefore,V863 is likely to be a promising high performance HTMs in PSCs.Our theoretical investigation of HTMs is helpful for understanding the hole transporting behaviors and developing higher performance HTMs.