First Advisor

Erik Johansson

Date of Publication

Winter 2-27-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.) in Chemistry

Department

Chemistry

Language

English

Subjects

Quantum dots, Nanoscience, Photovoltaic cells, Surfaces (Technology)

DOI

10.15760/etd.6124

Physical Description

1 online resource (xiv, 95 pages)

Abstract

Photovoltaic (PV) devices based on PbS quantum dot (QD) solids demonstrate high photon-to-electron conversion yields. However, record power conversion efficiencies remain limited mainly due to bulk and interfacial defects in the light absorbing material (QD solids). Interfacial defects can be formed when a semiconductor, such as QD solid, is contacted by another material and may predetermine the semiconductor/metal or semiconductor/metal-oxide junction properties. The objective of the work described in this dissertation was set to explore whether electrochemical contacting using liquid electrolytes can provide sufficient means of contacting the QD solids to investigate their PV performance without introducing the unwanted interfacial defects. I have initially focused on optimizing processing conditions for efficient QD solids deposition and studied their photovoltaic properties in a standardized solid-state, depleted heterojunction solar cell configuration. Further, a liquid contacting method was developed to study the relationship between photovoltages of QD solids and the energetics (e.g. reduction potentials) of the liquid contacting media. This electrochemical contacting of PbS QD solids was achieved by using anhydrous liquid electrolytes containing fast, non-coordinating, outer-sphere redox couples. Depending on the energetics of a redox couple, both rectifying and non-rectifying (Ohmic) PbS QD solid/electrolyte junctions were successfully formed with both p- and n-type QD solids. Furthermore, application of the liquid solution contacting method in studies of the PbS QD solids has unprecedentedly demonstrated that an ideal behavior of the photovoltage changes with respect to the changes in the energetics of the contacting media can be achieved. This fact supports the initially proposed hypothesis that such liquid contacting method will not introduce surface defects to the studied QD materials, allowing for their intrinsic properties to be better understood. The applicability of this method to both p- and n- type QD solids was demonstrated. Finally, a better understanding of the relationships between the surface and ligand chemistries of both p- and n-type QD solids and their photovoltaic properties was possible via applications of such method in conjunction with XPS and UPS studies.

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Persistent Identifier

http://archives.pdx.edu/ds/psu/24548

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