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SPIE Professional July 2013

Recommended: Journal of Photonics for Energy

Logo for SPIE Professional R&D Highlights

The foundations of transformation optics, non-imaging optics, and advanced dynamics can be found in a celebrated memoir on optics presented to the Royal Irish Academy by Sir William R. Hamilton in 1824.

By introducing the time of travel in terms of initial and final point (now called the point eikonal), Hamilton was able to produce all the well-known results of Hamiltonian optics and mechanics.

Starting with a prescribed wave front, and by judicious application of Huygens principle, the future wave fronts follow. SPIE member Vladimir Oliker’s seminal papers carry this work forward and show how the intensity distribution of a beam can be shaped and manipulated.

His recent paper in the Journal of Photonics for Energy,Ray mapping and illumination control,” provides an excellent example of beam shaping/manipulation.

Oliker and Jacob Rubinstein of Emory University (USA), with coauthor Gershon Wolansky of Technion-Israel Institute of Technology (Israel), present two classes of non-imaging design problems and show how ray mapping can be calculated independently of lens design, greatly simplifying the design task.

The mathematics is powerful and elegant, and the applications are of practical importance in illumination and energy conservation.

Designers of illumination optics such as automotive headlights and luminaires that light indoor and outdoor spaces will benefit from studying and implementing the methods described in this paper.

Source: Journal of Photonics for Energy 3(1), 035599 (2013) doi:10.1117/1.JPE.3.035599

–Roland Winston

SPIE member Roland Winston of University of California, Merced (USA), will present an invited talk at SPIE Optics + Photonics 25 August on how William R. Hamilton’s memoir to the Royal Irish Academy led to transformation theory and non-imaging optics.

Promising new design for up-conversion in PVs

PV production in Europe seems to be going down the drain. Is there hope for a revival through revolutionary new designs?

Martin Green, the Australian researcher and godfather of third-generation photovoltaics (PVs), has promoted novel performance-enhancing strategies for several decades. Among these approaches is up-conversion (UC) of photons with energy below the bandgap of the light-harvesting material by intermediate electronic bands or spectral conversion.

Up-converting materials, which are highly efficient under incoherent, low-intensity illumination, are in great demand. Lanthanide-based phosphors have been employed as UC materials to improve the performance of crystalline silicon (Si) solar cells, but they are weak absorbers, giving rise to low quantum yields.

In a recent paper in the Journal of Photonics for Energy, an Australian-German collaboration led by Timothy Schmidt at University of Sydney and Klaus Lips from Helmholtz-Zentrum Berlin presents a new approach based on triplet-triplet annihilation up-conversion (TTA-UC) in multi-component organic systems, which is promising for PV and water-splitting applications.

It offers greater efficiency under non-coherent and low-light illumination conditions, as well as spectral versatility. Higher quantum yields (QY) were achieved using TTA-UC when compared to PVs using inorganic lanthanide-based phosphors.

Still, the photocurrent enhancement by UC has to be increased by about two orders of magnitude and new device integration strategies have to be developed for widespread adoption of this approach in PVs.

The journal article, “Micro-optical design of photochemical up-converters for thin-film solar cells,” reports on the application of a focusing micro-structured back reflector fabricated by a simple indentation process, in combination with a TTA up-converter behind a thin-film Si PV cell.

It not only demonstrates an improvement of solar-cell photocurrent in the presence of the up-converter, but also highlights a pathway for a feasible device-integrated optical enhancement scheme, exploiting the inherent nonlinearity of the UC process.

By employing a reflecting focusing device, the QY of the up-converter can be increased, while the spectral regions outside the absorption of the UC unit are reflected, thus increasing light harvesting across the solar spectrum. While the presently reached photocurrent improvements are still minute, the general approach of such optically enhanced UC layers is sound and offers a good option for efficient solar-energy conversion.

Silke Christiansen 

Silke Christiansen of the Max Planck Institute for the Science of Light (Germany) is a member of the Journal of Photonics for Energy Editorial Board.


Special sections for Journal of Photonics for Energy 

The Journal of Photonics for Energy (JPE) is an e-journal that covers fundamental and applied research areas focused on the applications of photonics for renewable energy harvesting, conversion, storage, distribution, monitoring, consumption, and efficient usage.

Recent special sections of the journal were on high and low concentrator systems for solar electric applications, guest edited by Kaitlyn VanSant of the National Renewable Energy Laboratory (NREL) (USA), and on reliability of photovoltaic cells, modules, components, and systems.

The latter special section was guest edited by SPIE member Neelkanth G. Dhere of the University of Central Florida (USA), John H. Wohlgemuth of NREL, and Kevin Lynn of the U.S. Department of Energy.

Special sections scheduled for 2014 will cover:

  • Smart photonic systems
  • Solid-state lighting
  • Nanophotonics and cell technologies for solar energy conversion

SPIE Fellow Zakya Kafafi is editor-in-chief.

—Have a question or comment about this article? Write to us at spieprofessional@spie.org.

—To receive a print copy of SPIE Professional, the SPIE member magazine, become an SPIE member.

DOI: 10.1117/2.4201307.28

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