Synthesis And Application Of Carbalzole-based Hole-transporting Materials For Perovskite Solar Cells

Solar energy is promising alternative to conventional fossil fuel because of its inexhaustibility and environment-friendly features.In recent years,perovskite solar cell?PSC?has become a hotpot of photovoltaic research.Researchers make lots of efforts to enhance the performance of PSC.As an important part of PSC,hole-transporting materials?HTMs?have been widely investigated.HTMs are responsible for extracting and transferring hole from perovskite active layer.Spiro-OMeTAD is one of most state-of-the-art and successful HTM in n-i-p regular PSC structure,which has been extensively applied and studied.However,the expensive synthetic cost caused by complex synthesis and purification limited the large-scale application in the future.Researchers are committed to find cheaper and more efficient HTMs to replace spiro-OMeTAD.Diphenylamine-substituted carbazole?DPACZ?derivative is one of most competitive HTMs,owing to its cheap cost,facile synthesis and excellent performance.In this work,four novel DPACZ HTMs?M111-114?were designed and synthesized,which combined single DPACZ arm and four different S,N-heterocycle lateral group?phenothiazine?PTZ?and dithieno[3,2-b:2?,3?-d]pyrrole?DTP??of carbazole.Density functional theory calculations showed M111-114 are donor-acceptor?D-A?type molecules,in which significant charge transfer took place.Photophysical and electrochemical measurements demonstrated that S,N-heterocycle terminal groups and DPACZ group determined LUMOs and HOMOs,respectively.Differential scanning calorimetry and thermogravimetric analysis demonstrated that M111-114 had good thermal stability.M114displayed higher values than M111-113 in both hole mobility and conductivity measurements.IncorporatingM111-114,PSCdevicesbasedonthestructureof FTO/SnO₂/PC₆₁BM/Perovskite/HTM/Au had been fabricated.The PSC device based on M114 exhibited the best photovoltaic performance with open showing a power conversion efficiency?PCE?of 17.17%,with V_oc?open circuit voltage?of 1.055 V,J_sc?short circuit current density?of 22.24 mA cm^-2,and fill factor?FF?of 0.732.Open circuit voltage decay?OCVD?and electrochemical impedance and spectroscopy?EIS?measurements were conducted and PSC device based on M114 showed the least carrier recombination at interface between perovskite layer and HTM layer.Steady-state photoluminescence?PL?and time-resolved transient photoluminescence?TRPL?measurements were performed and M114exhibited the most efficient hole-extracting capacity.Contact angle measurements with water confirmed that M111-114 had better hydrophobic property than spiro-OMeTAD.PSC device based on M114 retained over 90%initial PCE after more than 600 h storage in ambient without encapsulation.