Stanford R. Ovshinsky Sustainable Energy Fellowship Talk: Photonic structures for solar concentrators and photovoltaic modules

The solar spectrum is a broad and diffuse light source, but solar panels operate most efficiently at wavelengths near the semiconductor bandgap and over a limited range of incident angles. This talk will discuss the use of spectrally selective, photonic surfaces to harvest sunlight for photovoltaics. The first part will discuss the implementation of selective mirrors into luminescent solar concentrators (LSCs), which shift the inefficiently converted, high energy sunlight into a spectrally narrow, focused light source at wavelengths that are more efficiently utilized by the solar cell. The second part will discuss the integration of photonic mirrors into photovoltaic modules to reflect the infrared portion of the spectrum that contributes to solar cell heating.

This talk will discuss luminescent concentrators made from both Si nanocrystals and from CdSe/CdS core/shell nanocrystals. We will first discuss the fabrication and characterization of nanocrystal – polymer composites with low light scattering, and then the design of spectrally-selective mirrors on the top surface that transmit blue light and trap the luminescent light inside the concentrator. We will show how the design of the spectrally-selective mirror changes for different luminophore properties, as well as the design of back mirrors based on gradient metasurfaces to steer light toward the edges.

The second part of the talk will discuss spectrally-selective structures used for light management in photovoltaic modules. These structures are designed to enhance transmission of sunlight above the bandgap of Si to improve photocurrent, and enhance reflection of light below the bandgap to reduce module operating temperature. We will show how the structures change at different interfaces within the module, the importance of designing mirrors that operate under diffuse illumination, and the effect of geographical location on mirror performance.