UC San Diego
InGaAsP/InP intrastep quantum wells for enhanced solar energy conversion
- Author(s): Chen, Winnie Victoria
- et al.
This dissertation explores innovative ways of improving efficiency of solar energy harvesting devices and evaluates them both analytically and experimentally. Two devices of different energy-harvesting mechanisms are presented : (1) intra-step quantum well (IQW) photovoltaic solar cell and (2) solar spectral condenser with IQWs. The IQW structure, step-like Type 1 (straddling gap) heterojunction structure, is used in both devices in order to help increase the conversion efficiency from solar photons to harvestable energy. Chapter 1 introduces the context of the research done, outlining an overview of past and present achievements in solar energy research. Chapter 2 describes the physical principles of the ideal solar cell, how to increase its efficiency, and figures of merit. In Chapter 3 the effect of IQWs compared with regular QWs in the solar cell are calculated using Schodinger's equations. In Chapter 4 the experimental results comparing bulk InP, regular QW, and IQW solar cells are presented and discussed. The solar cell sample with IQWs proved to have better efficiency than the cell with regular QWs and the bulk InP cell. In Chapter 5 the solar spectral condenser, which converts random, broad- spectrum solar light into guided, narrow spectrum photons to be collected by optical fibers, is studied. Design and expected performance of the solar spectral condenser device based on a slab waveguide with absorbing IQWs is presented. In Chapter 6, fabrication, experimental setup, and measurement results for the solar spectral condenser device are presented and discussed. The solar spectral condenser proved to amplify the seed laser at the expected wavelength when exposed to concentrated solar illumination. Chapter 7 summarizes the dissertation and outlines some future work. The goal of this research is to break new ground in solar cell research by studying a new structure, the IQW, for photovoltaic cells, and inventing a new device, the solar spectral condenser. The calculations and simulations were done based on principles in optoelectronics, which focused on photodetectors and lasers, but are applied to solar cells. The measurement setup for the solar spectral condenser is a completely new and original idea