New quantum dot nanomaterials to boost solar energy harvesting

Abstract

Fossil fuels are the most highly used sources for energy generation. But as energy needs increase day by day, and fossil fuels are consumed at ever faster rates, there is a great need for alternative energy sources. Renewable sources such as wind and solar can be exploited in a wide range of geographical areas and could effectively replace fossil fuels. For example, the Earth receives over 8 million quads of BTU (British thermal units) annually, meaning that there is enough solar energy available to fulfill all the energy requirements of the human race. However, due to the low efficiencies with which current solar cell technologies convert light into electricity, only a small fraction of the available solar energy can be harnessed. Deployment of solar cells will increase if their efficiency can be improved without increasing their cost. A novel concept known as the intermediate band solar cell (IBSC) paves the way for increasing solar cell efficiency.1 In an IBSC, sub-bandgap photons that would be wasted in a conventional solar cell can be harvested effectively to create a higher photocurrent. Semiconductor quantum dots (QDs) are perhaps the best choice to create an intermediate band in a single-junction solar cell due to the inherent tunability of their shape, size, and quantum confinement properties. For an IBSC to work, the QD system being used must satisfy certain conditions in terms of bandgaps and band alignments. For maximum efficiency, the QD and host material bandgaps should be 0.7 and 1.93eV, respectively. There have been numerous attempts to use established QD systems for IBSCs, including indium gallium arsenide/gallium arsenide—In(Ga)As:GaAs)—gallium antimonide/gallium arsenide (GaSb:GaAs), and indium arsenide/gallium arsenide Figure 1. Schematic of our aluminum arsenide/antimonide (AlAsSb, with the composition AlAs0:56Sb0:44) p-i-n intermediate band solar cell (IBSC). This cell contains 10 layers of indium arsenide (InAs) quantum dots (QDs). Gallium arsenide (GaAs) and gallium arsenide/ antimonide (GaAs0:95Sb0:05) cladding layers are used below and above the QDs, respectively, for better morphology and to tune the photoluminescence spectra.