The development of photovoltaics as an energy source has been propelled by numerous technological advancements over the past 60 years to now enable the conversion of sunlight into power at an efficiency of 46%. This enables power production that is cleaner, and more transferrable to locations off the grid than ever before, however new technologies are required to further increase efficiency while driving down costs. Currently a large effort is being made to achieve intermediate band solar cells (IBSC) that more efficiently convert energy from the entire solar spectrum. This is enabled through multiple techniques, including quantum dots (QDs), and potentially through doping superlattice solar cells. Doping superlattices have been explored theoretically and some historic work has used these superlattices to form nipi solar cells with alternating n-type, intrinsic, p-type, intrinsic layers. Multiple purposes exist for evaluating nipi solar cells, which include radiation hardness, an electronically adjustable absorption edge, use with nanostructures, and the possibility of an IBSC. The primary motivation for this work is to develop the nipi solar cell for evaluation as an IBSC, while also evaluating the radiation tolerance of the design for potential use in space applications. This has been completed through a theoretical and experimental analysis of nipi superlattice layers, and an extensive evaluation of the fabrication and growth processes required to achieve a high efficiency solar cell. Additionally an improved model for nipi diodes and solar cells has been developed. Also a novel process for fabricating nipi solar cells through epitaxial regrowth and diffused junctions has been developed, where record efficiencies for nipi solar cells have been measured for devices fabricated via epitaxial regrowth at 12.5%. An understanding of the effect of adding QD into a nipi superlattice has been obtained. Finally a greater understanding of the intrinsic radiation hardness of the nipi design has been achieved and possible methods to improve it have been evaluated. The techniques and processes developed here have the possibility to be used to further the understanding of nipi devices, and lead to the potential development of an IBSC with a QD-nipi design.

Library of Congress Subject Headings

Solar cells--Design and construction; Superlattices as materials; Gallium arsenide

Publication Date


Document Type


Student Type


Degree Name

Microsystems Engineering (Ph.D.)

Department, Program, or Center

Microsystems Engineering (KGCOE)


Seth M. Hubbard

Advisor/Committee Member

David V. Forbes

Advisor/Committee Member

Stefan F. Preble


Physical copy available from TK2960 .S56 2015


RIT – Main Campus

Plan Codes