Case 12087

Solar cell efficiencies through periodicity


Solar cells, photovoltaics, energy conversion efficiency, periodicity, photonic crystals, near-infrared


Significantly enhances thin-film silicon solar cell efficiencies (up to 35%)


    One of the most widely used materials for solar photovoltaic (PV) cells is crystalline silicon (Si). However, its absorption is weak in the red and near-infrared (comprising 36.2% of solar photons above the Si bandgap). This problem is particularly acute for thin-film micromorph or microcrystalline thin-film silicon solar cells. It would be very desirable to improve their design so that they use less Si while effectively absorbing and converting as many photons as possible into current in order to boost the power conversion efficiency.


This invention is a novel method of using photonic crystals in solar cell design to enhance the absorption of solar photons, particularly for the red and near-infrared. The redesigned solar cell includes a planar PV material region covered by a uniform anti-reflection coating. A photonic crystal structure is positioned below the PV material region and reflects light at targeted wavelengths into totally internally-reflected modes, which bounce back and forth within the PV cell until fully absorbed.


Offers up to 35% relative enhancement of thin-film silicon solar efficiencies (micromorph or microcrystalline)

Can be made at low cost through self-assembly (targeted at $5/m2 or $0.05/W for large-scale production)

  • Professor John D. Joannopoulos (Director of ISN and Department of Physics, MIT)
  • Dr. Peter Bermel (Research Laboratory of Electronics, MIT)
  • Dr. Chiyan Luo (Vice President, Bank of America)

Intellectual Property:
  • U.S. Published Application Serial Number 11/400911, filed April 10, 2006
  • European Patent Office Application Number 07759997.5, filed October 10, 2008
  • Japanese Patent Office Application (based on PCT/US2007/065830), filed October 10, 2008


Peter Bermel, Chiyan Luo, Lirong Zeng, Lionel C. Kimerling, and John D. Joannopoulos, "Improving thin-film crystalline silicon solar cell efficiencies with photonic crystals", Optics Express 15, 16986 (2007).

Related Cases:

13573: Global optimization of silicon photovoltaic cell front coatings

Last revised: January 20, 2012

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