Organic electronic devices and their interfaces.

摘要

After twenty years of development, significant progress has been made in the design and fabrication of organic electronic devices. High performance LEDs, solar cells, transistors and memory devices have been developed. One of the fundamental subjects for organic electronic technologies is the understanding of interfaces involving semiconducting organic molecules and polymers. This dissertation focuses on two types of organic electronic devices: organic solar cells, vertical organic transistors and their interface properties. A comprehensive introduction and review of the organic electronics is presented in Chapter 1.;Chapter 2 and Chapter 3 of this dissertation discuss the poly(3-hexylthiophene) (P3HT): fullerene derivative bulk heterojunctions (BHJs) used in polymer solar cells. In Chapter 2, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) are used to study the BHJs formed by blending the two materials. The analysis reveals the P3HT enrichment at the free (air) surfaces and abundance of fullerene derivatives at the organic/substrate interfaces. The vertical phase separation is attributed to the surface energy difference of the components and their interactions with the substrates. This inhomogeneous distribution significantly affects photovoltaic device performance and makes the inverted device structure a promising choice. In Chapter 3, the energy level alignment in the BHJs is investigated using the ultraviolet photoelectron spectroscopy (UPS). The results show that the energy level alignment in the BHJs is affected by the vertical phase separation and the integer charge transfer model can be employed to explain the phenomena.;The studies of vertical organic transistors are demonstrated in Chapter 4 and Chapter 5. In Chapter 4, XPS and UPS are used to investigate the operation mechanism of the vertical field-effect transistors. It is found that a capacitor with a thin and rough electrode can be used to tune the charge injection barrier between the thin electrode and the organic layer deposited on it. The results explain the switching behavior in vertical organic transistor, and offer an important approach to control the charge injection process in organic electronic devices. Based on this study, a vertical organic light emitting transistor is demonstrated in Chapter 6. This unique device exhibits dual functions, emitting light as an OLED and switching current as a transistor. The device not only provides a new solution for display applications but also proves the proposed working mechanism of vertical organic transistors.