The Growth And Electronic Structure Of Organic Thin Films On SiO_x Substrate

Organic optoelectronic devices are getting more and more attention in recent years.Compared with traditional inorganic devices,organic devices are characterized by high efficiency,low production cost and good flexibility.Nowadays,OLEDs are replacing traditional LCDs gradually.For example,recently Samsung and Huawei released folding screen phones with OLED displays.Traditional LCD screens cannot be bent and folded.Although a lot of research has been done in the area of organic devices,there are still many key issues that remain unresolved.The research on the electronic structure properties of organic materials and their interfaces in organic semiconductor systems has always been one of the most important topics,but many years of effort have failed to gain a clear understanding.The molecular coupling energy of organic materials at the interface determines the efficiency of photovoltaic devices,but the perfect donor-accepter pairs are remain undiscovered.The electronic structure properties of organic thin films have a great relationship with their molecular orientation.There is only a weak interaction between the organic molecule and the SiOx substrate,and it only grows upright on this kind of substrate.In this case,we can get a better look at the electronic structure properties of organic materials and organic-organic heterojunction structures.In order to study the mechanism of these organic materials and the organic-organic interfaces,we used ultraviolet photoelectron spectroscopy(UPS),Grazing incident X-ray diffraction(GIXD),X-ray Reflectivity(XRR)and Atomic Force Microscopy(AFM)to finish three related experimentsFirst experiment used three different para-sexiphenyl(6P)derivatives(m-2F-6P,o-2F-6P and CN-6P)grown on SiOx substrate to study the impact of partial fluorination on growth and electronic structure.The result shows that m-2F-6P thin film is smoother than the o-2F-6P thin film.There are more island structure on the surface of o-2F-6P thin film.In the second part,we used 6phenacene and picene as donor materials,perfluoropentacene as acceptor material to study the co-deposition on the SiOx substrate.It has been found that the co-deposition of these two materials can change the ionization energy of the co-deposition layer without changing the energy level of the upper PFP thin film.The change of ionization energy related to the ratio of the two materials in co-deposition.In the last part,PFP was used as the top layer,6Phen and PEN were used as bottom layer,respectively,to study their heterojunction properties when grown at different substrate temperatures on SiOx substrates.The experimental data shows the thin film get smoother when grow in high substrate temperature than in low substrate temperature.And the interface dipoles between the two materials will also be affected by temperature.Higher the temperature,Shorter the dipole moment.