Date of Award

Spring 1-1-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

First Advisor

Arthur J. Nozik

Second Advisor

Joseph M. Luther

Third Advisor

Gordana Dukovic

Fourth Advisor

Garry Rumbles

Fifth Advisor

Michael Marshak

Abstract

Semiconductor quantum dots (QDs) are interesting materials that, after less than 40 years of research, are used in commercial products. QDs are now found in displays, such as Samsung televisions and the Kindle Fire, and have applications in lighting, bio-imaging, quantum computing, and photovoltaics. They offer a large range of desirable properties: a controllable band gap, solution processability, controlled energy levels, and are currently the best materials for multiple exciton generation. The tunable optoelectronic properties of QDs can be controlled using size, shape, composition, and surface treatments—as shown here. Due to the quasi-spherical shape of QDs the surface to volume ratio is high, i.e. many of the constituent atoms are found on the QD surface. This makes QDs highly sensitive to surface chemistry modifications. This thesis encompasses the effects of surface treatments for QDs of two semiconducting materials: lead chalcogenides and CsPbI3.

Our group developed a new synthetic technique for lead chalcogenide QDs via the cation exchange of cadmium chalcogenides. An in-depth chemical analysis is paired with optical and electrical studies and we find that metal halide residue contributes to the oxidative stability and decreased trap state density in cation-exchanged PbS QDs. We exploit these properties to make air-stable QD photovoltaic devices from both PbS and PbSe QD materials.

Beyond the effects of residual atoms left from the synthetic technique, I investigated how to controllably add atoms onto the surface of QDs. I found that by introducing metal halides as a post-treatment in an electronically coupled array I am able to control the performance parameters in QD photovoltaic devices. These treatments fully infiltrate the assembled film, even under short exposure times and allow me to add controlled quantities of surface atoms to study their effects on film properties and photovoltaic device performance.

Finally, I sought to apply the knowledge of the lead chalcogenide QD surfaces to produce QD photovoltaics from a new material: CsPbI3. I fabricated the first perovskite QD photovoltaic devices and using similar treatment methods as the lead chalcogenide QD arrays, I am able to influence the photophysical properties of CsPbI3 QD arrays.

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