Interfacial Electronic Structure Of Organic Acceptor Materials PC₆₁BM And ITIC On Metals Or Inert Substrates

Organic/metal interface and organic/inert material interface exist widely in organic field-effect devices and organic solar cells.Energy level alignment at the interface plays a crucial role in the process of charge transport and then largely determines the performance of the devices.In this thesis,I have investigated the electronic structure of the interfaces between PC61BM or ITIC and some substrates.Here the fullerene derivative PC61BM is an electron-acceptor material(n-type semiconductor)extensively applied in organic electronic devices.ITIC is also an electron-acceptor material which exhibits some advantages in organic solar cells as compared with PC61BM.The research methods adopted in this thesis include synchrotron radiation photoemission spectroscopy(SRPES),X-ray absorption spectroscopy(XAS)and density functional theory(DFT)calculations.For the organic/inert material interface,the Integer Charge Transfer(ICT)model decides the energy level alignment.In this model,one important concept for an electron-acceptor material is the negative integer charge transfer energy level(EICT-).We have measured the EICT-of ITIC with SRPES,which is determined to be 4.00±0.05 eV.The molecular orientation in ITIC film has been studied with XAS measurements.The molecules predominantly have the face-on orientation on inert substrates.For helping to understand the experimental data,we performed DFT calculations for the electronic structure of isolated ITIC molecule.It is found that the electron correlation effect plays crucial role in the electronic structure,while the polaron effect is negligible.For the organic/metal interface,we carried out detailed researches on the interfacial electronic structure of PC61BM/metal systems.The metal substrates are Au(lll),Ag(111),Au(100)and Ag(100).These interfaces are chemisorbed.The TSI + ICT method(the combination of the two sub-interfaces(TSI)model and the ICT model),which was proposed formerly by us,can be used to explain the energy level alignment of these interfaces.In addition to expanding the connotation and application scope of the TSI+ICT method,this part of the work also reveals that the intrinsic dipole moment of the PC61BM molecule affects the molecular arrangement at the interface,which in turn has a great influence on the interfacial electronic structure.At last,we studied the electronic structure of the more complex interfaces of Ca/PC61BM(prepared by depositing Ca on the PC61BM film)and PC61BM/Ca(prepared by depositing PC61BM on the Ca film).Difffus.ion of metal atoms into the PC61BM film is significant for these interfaces.We propose the transition layer(TL)model to deal with the energy level alignment.According to the TL model,there is no energy barrier for the electrons to transport from the interior of the PC61BM film to the Ca film;the interface is Ohmic contact.