Perovskite solar cells gain great academic concern due to its excellent optical and electrical properties.The efficiency of solar cells using organic-inorganic perovskite as light absorbing layer has reached to 22%.A key technology has been developed by the replacement of the liquid electrolyies with solid state hole-transporting materials(HTMs),which not only improves the power conversion efficiency(PCE)but also enhances the cell stability.HTMs have been an integral part of PSCs.To date,the most commonly used HTM is Spiro-OMeTAD,which has been widely investigated due to the good solubility in organic solvents and proper electronic energy level,which is well matched to the perovskite light absorbing layers.However,the synthesis of Spiro-OMeTAD is relatively expensive due to harsh synthetic conditions,and it has low hole mobility.Therefore,the development of new economical and efficient HTMs with ideal electronic properties remains an attractive and challenging goal.In this thesis,the effects of thiophene chain lengths,molecular configuration,and the methoxy number and position on the photoelectrical properties of HTMs,as well as the energy levels and hole transport properties of HTMs with spiro-cores are investigated by using density functional theory and Marcus theory.The main results are summarized as follows:(1)The effect of thiophene chain lengths on the optical and hole transport properties of HTMs(H111、H112、H113、H114,and H115)were investigated by density functional theory and Marcus theory.The results show that the extension of thiophene chain can lower the HOMO-LUMO energy gap and extend the absorption spectrum towards longer wavelengths.The reorganization energy and exciton binding energy gradually decrease as the number of thiophene ring increases,and there is a well linear relationship between the reorganization energy and the number of thiophene ring.The hole mobility H114 and H115is higher than that of H111 and H112.H114 and H115 are promising HTM candidates for the fabrication of efficient perovskite solar cells.In addition,the shortest S-S distances in stacked dimer are found to be contrariwise proportional to hole mobility,which indicated that S atom plays an important role in increasing hole mobility of HTM.These results are expected to be helpful for further rational design of novel HTMs.(2)The electronic properties and hole mobility of two isomeric molecules H112 and KTM3 have been theoretically investigated by using Marcus theory combined with density functional theory.The results shown that the exciton binding energy of H112 is 23.6%smaller than that of KTM3,which suggests that the electron-hole pairs are easier to dissociate into free charge carriers in H112.More importantly,the hole mobility of H112 is up to 6.75×10-2 cm2V-1s-1,which is larger than that of KTM3.This indicated that H112 has better hole tranport property that KTM3.On the basis the differences of hole transport porperties of H112 and KTM3,and differences of short-circuit current density of based-them cells,it can be concluded that the small exciton binding energy and the large hole mobility of HTM contribute to the enhancement of the short-circuit current density of the device.(3)The electronic properties and hole mobility of three spiro-type organic hole transport materials including Sprio-F1,Spiro-F2 and Spiro-F3 were explored by using density functional theory and Marcus theory.Compared with the calculated and experimental HOMO levels of 30 reference molecules,an empirical equation is proposed to accurately predict the HOMO levels of hole transport materials.Furthermore,a simplified method is presented and adopted to qualitatively compare molecular hole mobility.The results suggest that the HOMO levels of Sprio-F1,Spiro-F2 and Spiro-F3 is lower than that of Spiro-OMeTAD,and the hole mobility of Spiro-1 and Spiro-3 is higher than that of Spiro-OMeTAD.Spiro-1 and Spiro-3 are promising HTM candidates for the efficient perovskite solar cells.(4)The frontier molecular orbital energies and hole mobility of HTM1 and new designing eleven spiro-type HTMs were investigated by using density functional theory and Marcus theory.The results shown that the HOMO levels of HTMs can be affected by the number and position of methoxy.Specifically,m-substitution is beneficial to reduce the molecular HOMO and LUMO levels,the number of substituents has almost no effect on the LUMO level.Moreover,the hole mobility can be improved by o-substitution or mixed o-and p-substitution.These results indicate that the HOMO levels and hole mobility of HTMs can be controlled by adjusting the number and position of the methoxy groups.These findings are expected to be helpful for further rational design of novel HTMs for high-performance PSCs. |