Synthesis And Application Of Hole Transport Materials Based On Tetrathiophene Eight-membered Ring For Perovskite Solar Cells

Perovskite solar cell(PSC)is a new type of all-solid-state thin film cell,which is known as "the new hope in the field of photovoltaics" due to its strong absorbance,high carrier mobility and broad development prospects.The hole transport layer(HTL)is one of the important components of PSCs.The main function of HTL is to collect and transport holes,to realize efficient separation of electrons and holes.Organic small molecules are with the merits of easily energy levels tuning,good solubility,and facial process.Their characterization methods are also relatively mature.Therefore,they can be used as HTL for perovskite solar cells.However,there are few reports about efficient,stable and cheap hole transport materials based on thiophenes.In this paper,a rigid three-dimensional thiophene eight-membered ring based on thiophene was selected as the research object.Two target compounds,COTT-1 and COTT-2,were successfully designed and synthesized.Their photophysical,electrochemical,and thermal properties were systematically investigated in a combination of experimental and simulation methods.The properties of perovskite solar cells based on these two materials as hole transport layer were tested.Under the same conditions,the power conversion efficiency(PCE)of the devices are 8.4% and 17.7% respectively.And the COTT-2 as an HTL device exhibits excellent performance comparable to Spiro-OMe TAD(18.2%).Subsequently,we prepared a modified perovskite absorber layer using COTT-1 as an interfacial layer,and COTT-2 as the HTM.Under the same working conditions,it produced 19.2% PCE,which is significantly better than the traditional Spiro-OMe TAD-based devices.The corresponding devices were analyzed by photoluminescence,scanning electron microscopy and atomic force microscopy.These experiments proved the potential of hole transport materials with cyclooctatetrathiophene as the core.The new material can be applied as a hole transporting material with good performance to improve the PCE of perovskite solar cells.It has both theoretical and practical significance for the development and utilization of solar energy.