Theromophotovoltaic Enhancement: 2D Photonic Crystals to Increase TPV Efficiencies
- PDF / 385,869 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 115 Downloads / 198 Views
1208-O16-06
Theromophotovoltaic Enhancement: 2D Photonic Crystals to Increase TPV Efficiencies Corey M. Shemelya and Thomas E. Vandervelde Tufts University, Department of Electrical and Computer Engineering, Medford, MA, 02155, U.S.A. ABSTRACT Here, we report on the enhancement of photon conversion by integration of photonic crystal (PhC) and surface plasmon (SP) structures into thermophotovoltaic (TPV) cells. PhCs consisting of rods of air are incorporated into the base of semiconductor TPV cells to increase the duration of thermal photon absorption, thus significantly enhancing quantum and conversion efficiencies (QE and CE, respectively). The potential of PhCs to augment the CE of TPV cells for most IR wavelengths makes it a widely useful technology. The ability to turn waste heat into usable energy will improve efficiency in a variety of electrical and electromechanical systems. INTRODUCTION For many years researchers have attempted to efficiently harvest waste heat and transform it into usable energy using TPVs. TPV devices harvest infrared photons, converting their energy into electricity in a manner similar to that of photovoltaic devices (PVs), but utilizing lower energy photons.1 Incident photons create electron-hole pairs, which are then separated by the natural potential of the depletion region. The resulting charge carrier is subsequently removed from the material by the top or bottom contact, thus creating a current. Low QE (the probability that a photon will be absorbed) in most TPV cells is the biggest stumbling-block to achieving an economically viable device, and directly affects the CE (the probability that a photon will be converted into a carrier that is collected). TPV cells may CEs just above 20%.2 By increasing the CE, a TPV cell can operate at lower temperatures, with fewer incident photons, to produce the same current. Recent advances in micro-/nano-fabrication techniques have enabled the creation of novel structures to enhance the absorption and, therefore, the conversion of the incident thermal photons. In particular, PhC and SP enhancements at the interface of air and the semiconductor have been shown to increase the efficiency of photon-to-current conversions for GaAs dots-in-awell and dots-in-a-double-well infrared photodetectors.3 Here, we propose a simulated enhancement of GaSb TPV efficiency by integration of PhCs. EXPERIMENT Periodic arrays of either air or dielectric rods within a highly-contrasting index material, such as gold, can form a photonic band gap. Within this photonic band gap, photons are no longer allowed to propagate.4 When a photonic band crosses the gamma point (center) of the photonic band diagram the electric field forms a standing wave within the PhC that slowly loses energy to the rest of the structure. The wavelength at which this occurs can be tuned by altering the hole radius, r, and the lattice constant, a (shown in Figure 1).
Figure 1. top view of photonic crystal pattern showing the lattice constant (a) and hole radius (r).
A SP is a standing electroma
Data Loading...
