Electronic Structure of Organic Semiconductor Multi-Heterojunctions

Abstract

Abstract: Electronic Structure of Organic Semiconductor Multi-Heterojunctions Chaw Keong Yong, Department of Physics, submitted for the degree of Master of Science, 2009

This thesis investigated the electronic structure of organic semiconductor multi-heterojunctions which is critical for the control of charge injection, separation, and exciton recombination at the interface in various organic devices. Organic semiconductors based on sexithiophene (6T), fullerene (C60), tetrafluoro-tetracyanoquinodimethane (F4¬¿TCNQ), poly(9,9¿-dioctylfluorene) (F8), and poly(3-hexylthiophene) (P3HT) have been used to form the multi-heterojunctions in different combinations on poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDT:PSSM) conducting polymer surfaces in UHV chamber and characterized in-situ by Photoemission Spectroscopy.

With 6T and C60 as model system, the molecular orientation dependent charge transfer at the interface of organic donor-acceptor heterojunction was observed.m the time-dependent photoemission spectroscopy measurements that the interface dipole potential in a blend of donor-acceptor was widely distributed which resulted in broadening of the polaron energies. The phase segregation in donor-acceptor blended heterojunction also resulted in local built-in electric field. This suggests the Coulomb energy of polaron-pairs at the donor-acceptor interface could be inhomogeneous throughout the device blended heterojunctions.