Abstract

Photovoltaics are an essential enabling technology providing power both where it would be impractical to deliver otherwise and where sustainably produced--and recently, economically competitive--energy is demanded. Significant effort has gone into increasing the efficiency of these devices since their initial development in the 1950s. The most dramatic enhancements have been from the judicious choice of material used for photon collection, with current state of the art (SOA) conversion efficiencies reaching 46%. Further improvements may be engineered through exploration of next-generation methodologies, such as the incorporation of quantum dots (QDs), to maximally exploit the solar spectrum and develop solar cells producing both large current densities and large voltages compared to current SOA.

In this work, the electrical, optical, and mechanical properties of GaAs solar cells incorporating nanostructured InAs QDs, strain balanced with GaP, were studied. QDs allow for an increase in the current generation capabilities of the bulk GaAs semiconductor through absorption of sub-bandgap photons via bound states in the low-bandgap, low-dimensional material. QDs alter the recombination dynamics of charge carriers in the photovoltaic device, which typically led to an undesirable reduction in voltage of more than 200 mV. The addition of dopant, necessary to explore the effects of an intermediate band solar cell, showed a voltage recovery of 121 mV, with no positive or negative effects on sub-bandgap collection. Advanced characterization and data analysis techniques were developed, combining photoreflectance and temperature-dependent photoluminescence, to investigate the activation energy of bound states in the QD, which were shown to undesirably decrease by 34 meV to 40 meV with the addition of doping. Simulation of alternative structures that may help to increase this activation energy were performed using alternative strain balancing designs, and a general strain balancing model for strained nanostructured superlattices for a variety of material systems was developed.

Publication Date

5-14-2015

Document Type

Dissertation

Student Type

Graduate

Degree Name

Microsystems Engineering (Ph.D.)

Department, Program, or Center

Microsystems Engineering (KGCOE)

Advisor

Seth M. Hubbard

Advisor/Committee Member

Ryne P. Raffaelle

Advisor/Committee Member

Sean L. Rommel

Campus

RIT – Main Campus

Plan Codes

MCSE-PHD

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