Dissertation/Thesis Abstract

Interface Studies of Organic/Transition Metal Oxide with Organic Semiconductors and the Interfaces in the Perovskite Solar Cell
by Wang, Chenggong, Ph.D., University of Rochester, 2015, 231; 3723336
Abstract (Summary)

In recent decades, research and development of organic based semiconductor devices have attracted intensive interests. One of the most essential elements is to understand the electronic structures at various interfaces involved in these devices since the interface properties control many of the critical electronic processes. It is thus necessary to study the electronic properties of the organic semiconductors with surface analytical tools to improve the understanding of the fundamental mechanisms involved in the interface formation. This thesis covers the experimental investigations on some of the most interesting topics raised in the recent development of organic electronic devices. The thesis intends to reveal the physical processes at the interface and their contribution to the device performance with photoemission and inverse photoemission investigations on the evolution of the occupied and unoccupied electronic structures. I will report a substantial difference in the electron affinity of CuPc on two substrates as the orientations of CuPc are different. I will also illustrate that the CuPc has standing up configuration on one monolayer of C60 on SiO2 while lying down on one monolayer of C60 on HOPG. Meanwhile, the CuPc on more than one monolayers of C60 on different substrates show that the substrate orientation effect vanished. Then I will propose a two-stage model to describe the bulk doping effect of C60 by molybdenum oxide. I will also demonstrate that the doping effect of C60 by ultra-thin layer molybdenum oxide is weaker than that by interface doping and bulk doping. I will demonstrate that for Au on CH3NH3PbI3, hole accumulation occurs at the vicinity of the interface, facilitating hole transfer from CH3NH3PbI3 to Au. I will show a strong initial shift of core levels to lower binding energy in C60 on CH3NH3PbI3 interface, which indicates that electrons transfer from the perovskite film to C60 molecules. I will further demonstrate that the molybdenum oxide surface can be passivated by approximately two monolayers of organic thin films against exposure to air. I will discuss the mechanism that how oxygen plasma treatment effectively recover the high work function drop of molybdenum oxide by air exposure. At the end, I will show that a small energy offset at Pentacen/C60 heterojunction makes it easy to transfer electrons from Pentacene to C60 even under a small applied bias, facilitating the occurrence of charge generation. Finally, I will summarize the thesis.

Indexing (document details)
Advisor: Gao, Yongli
Commitee: Bigelow, Nicolas, Rothberg, Lewis, Shapir, Yonathan, Shestopalov, Alexander
School: University of Rochester
Department: Arts and Sciences
School Location: United States -- New York
Source: DAI-B 77/01(E), Dissertation Abstracts International
Subjects: Atoms & subatomic particles
Keywords: Interface, Organic semiconductor, Perovskite solar cell, Photoemission, Surface, Transition metal oxide
Publication Number: 3723336
ISBN: 978-1-339-06068-2
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