An ATR-FTIR study of semiconductor-semiconductor and semiconductor-dielectric interfaces in model organic electronic devices.

Abstract

Organic electronics offer many benefits to inorganic electronics such as the promise of cheap, large-scale processing on flexible substrates and incorporation into many household devices. Organic photovoltaic (OPV) devices and organic field effect transistors (OFETs) offer low-cost implementation which might compete in some applications with their inorganic counterparts. However, fundamental work is necessary to uncover the physics governing the operation of OPVs and OFETs, in order to improve the efficiency of the devices. Much of the fundamental understanding developed in this work occurs at buried interfaces, such as the donor acceptor interface in OPVs or the semiconductor dielectric interface in OFETs. This thesis first introduces the reader to the device physics and state of the art in the development of OPVs and OFETs. After describing the experimental techniques used, a discussion of interfacial electric fields in bulk heterojunction polymer/small molecular solar cells will follow. It was found using the vibrational Stark effect, that donor acceptor interfacial electric fields could be measured and related to previous experiments. The interfacial field hinders the dissociation of excitons but also prevents geminate pair recombination. In OFET devices, the semiconductor dielectric interface was studied and the rate limiting steps to device performance in polymer electrolyte gated OFETs were determined. The interfaces studied provide insight into the fundamental operation of both OPVs and OFETs, which should help produce more efficient and controllable production of organic electronic devices.