Skip navigation
Please use this identifier to cite or link to this item:
Authors: Zhang, Fengyu
Advisors: Kahn, Antoine
Contributors: Electrical Engineering Department
Keywords: Molecular Doping
Organic Electronics
Photoemission Spectroscopy
Surface Science
Subjects: Electrical engineering
Issue Date: 2021
Publisher: Princeton, NJ : Princeton University
Abstract: In the past decade, metal halide perovskites have attracted tremendous attention in the field of photovoltaics and light emission due to their superb optoelectronic properties and potentially low manufacturing costs. Perovskite solar cells have shown remarkable progress in recent years with rapid increases in power conversion efficiency, from reports of about 3% in 2009 to over 25% in 2020, making it the fastest improving solar cell technology in history. The understanding of surface and interface properties plays a very important role in the design of high-efficiency solar cells. To advance the development of such devices, the ability to understand, control and manipulate surface and interface properties is essential. The work presented in this thesis investigates the challenges and rewards of characterizing metal halide perovskite surfaces with high sensitivity measurements, such as Kelvin probe contact potential difference and photoemission spectroscopy measurements. We show the loss of halide species from the perovskite surfaces upon supra-gap illumination in vacuum, which causes both a long-term alteration of the surface and a modification of the Kelvin probe tip during measurement. These changes, if undetected, lead to a misinterpretation of the perovskite surface potential. In addition, we illustrated the difficulties in determining the density of states (DOS) in the valence band and at the valence band maximum (VBM) of these lead halide perovskite surfaces with ultraviolet photoemission spectroscopy. Our results stress the importance of taking into account the low DOS at the valence band edge and highlight issues such as film degradation, non-equilibrium situations under light, and the importance of removing all parasitic contributions to the photoemission spectra. We developed strategies that help to accurately measure the electronic structure of perovskite surfaces, with which we demonstrate the measurement of electronic gap states above the VBM of some perovskites. These results establish the link between these potentially detrimental gap states and an additive commonly mixed in the perovskite precursor solution. Finally, we review our previous work on molecular doping and demonstrate the surface doping of perovskites with molecular reductants and oxidants.
Alternate format: The Mudd Manuscript Library retains one bound copy of each dissertation. Search for these copies in the library's main catalog:
Type of Material: Academic dissertations (Ph.D.)
Language: en
Appears in Collections:Electrical Engineering

Files in This Item:
File Description SizeFormat 
Zhang_princeton_0181D_13600.pdf43.01 MBAdobe PDFView/Download

Items in Dataspace are protected by copyright, with all rights reserved, unless otherwise indicated.