Princeton University

School of Engineering & Applied Science

First Principles Evaluation of Nickel Oxide and Other Materials for Solar Energy Conversion

Nima Alidoust
Engineering Quadrangle, J401
Thursday, July 30, 2015 - 9:00am to 10:30am

Global climate change and pollution caused by fossil fuels necessitate the search for inexpensive, renewable energy sources. Devices that convert solar energy to fuels and electricity are among the possible solutions to this challenge. Engineering efficient devices for this purpose requires fundamental understanding of the materials involved, identification of ways to improve these materials, and discovery of new materials that could help achieve higher efficiencies and lower costs. The work presented in this dissertation contributes to these fronts via quantum mechanical calculations.In particular, we study nickel oxide (NiO), an inexpensive semiconductor, with favorable properties to enhance solar energy conversion efficiency. We identify and devise various theoretical models that accurately describe NiO’s properties. We use these models to show that alloying NiO with Li2O could make NiO a better light absorber, rendering it more appropriate for use in various solar energy conversion devices.
We study how efficiently holes (empty energy levels resulting from electron excitation upon light absorption) move through the crystal structure in NiO and NiO alloys. We show that the efficiency of hole movement in NiO can be enhanced by alloying NiO with Li2O at high enough concentrations. This makes NiO alloys with Li2O suitable for use as hole conductors. We also find that hole transport in NiO is confined to two dimensions. We predict that alloying NiO with MgO or ZnO leads to formation of semiconductors that like NiO are transparent to visible light. However, forming these alloys leads to three-dimensional hole transport, thereby increasing the efficiency of hole movement in NiO. This makes NiO alloys with MgO or ZnO suitable for use as transparent conducting oxides, components used in many solar energy conversion devices.
We introduce CoO and Co0.25Ni0.75O alloy as new intermediate band semiconductors (IBSCs), capable of absorbing light across multiple band gaps and enhancing light absorption in IBSC-based solar cells. Finally, we investigate the spatial concentration of hole and electron states in methylammonium (MA) lead iodide, a promising material for photovoltaic devices. We show that some orientations of the MA ion in the crystal structure may lead to spatial separation between hole and electron states. However, this separation is unlikely to impact the efficiency of MAPbI3 solar devices.