Omnidirectional, Polarization-Independent, All-Dielectric Light Trapping Scheme

Technology #33979

Novel biomimetic design approach enables manufacturers to cost-effectively produce ultrathin, flexible, durable solar cells that capture the most energy from daylight as it strikes from multiple directions.

UCF researchers have developed a novel architecture and process for producing low-cost, ultrathin, flexible and durable solar cells that can be easily fabricated using roll-to-roll processing. UCF’s new light trapping scheme uses nanoparticles to mimic the essential light trapping mechanisms found in a leaf: focusing, wave guiding and light scattering. Unlike conventional solar cell architectures, the invention incorporates the use of lightweight, pliable 2D semiconductor materials and an all-dielectric approach which is lossless in the visible spectrum of light. It also offers broadband polarization-independent reflection features, so that solar cells can capture sunlight from almost any angle.

Technical Details

The invention is a biomimetic light trapping scheme that can be applied to create ultrathin, lightweight, flexible and durable Schottky junction, P-N junction, or any other type of solar cells. By using two optically tuned layers, the light trapping scheme does not employ any nano-structuring of the active silicon substrate, thereby ensuring that the optical gain is not offset due to recombination losses. As well, complete decoupling of the optical and electrical systems enables independent optimization of the light trapping scheme. The scheme accommodates the use of a variety of materials for the two optical layers, with the ratio of the nanoparticle diameters playing a crucial role in achieving light trapping that is omnidirectional, polarization-independent, and more pronounced in the high wavelength regime.

In an example use of the invention, a graphene (Gr)/silicon (Si) heterojunction Schottky type solar cell was fabricated with a substrate thickness of 20 µm. As shown in Figure 1, the light trapping scheme consisted of a bilayer configuration of densely packed hexagonal arrays of titania nanoparticles and silica nanoparticles. The top silica layer played a composite role of focusing and funneling the light as that provided by the upper epidermis and palisade mesophyll of a leaf. The light was confined within the particles by total internal reflection and was trapped by the surface itself until it found a strong leakage channel provided by the bottom layer. The bottom layer enabled scattering—like the spongy mesophyll layer in a leaf. It scattered light in the forward direction into the underlying high indexed silicon substrate through the transparent graphene film. As a result, the ultrathin solar cell achieved a power conversion efficiency of ~9 percent. Its characteristics remained unaltered after 1000 bending and straightening cycles using a bend radius as low as 3 mm, demonstrating the stability, durability and reliability of the fabricated device.

Benefits

  • Produces ultrathin, flexible, lightweight, durable and reliable solar cells
  • Omnidirectional features enable solar cells to efficiently capture light at different angles
  • Cost-efficient, providing for the highest watt/gram silicon use
  • Enables mass-fabrication via roll-to-roll processing

Applications

  • Solar cell manufacturing and production
  • Wearable, flexible electronics