Supercell Diffractive Optics

About

About Thin film solar cells are an emerging technology that can enable low-cost and highly efficient solar cells. However, thin film solar cells require light trapping to compensate for the otherwise poor absorption in the active thin film. Our supercell design concept for light trapping can provide optimized performance that is compatible with low-cost and mass production techniques. Light absorption in thin films can be strongly enhanced when guided modes supported by the thin film are excited. This occurs when the diffraction angle of the light coupled by the grating matches the characteristic angle of the guided modes. Our invention – a novel design concept for diffraction gratings – explores large period gratings because these can excite more modes than typical light-wavelength scale gratings. To benefit from the larger period, we employ a supercell, i.e., a unit-cell consisting of fine features used to control the diffraction efficiency of the grating. The supercell is designed to shift the energy from the low diffraction orders, which cannot excite guided modes, to the higher diffraction orders, which are capable of exciting these modes. Key Benefits Simple design concept that can be implemented in any kind of solar cell Compatible with low-cost mass production technologies such as nano-imprint lithography Light trapping is substantially improved at no additional fabrication cost Absorption enhancement is stable against variation of light's angle of incidence Concept can be implemented in all types of gratings and combined with techniques such as randomized structures Applications Solar panels Solar cells Renewable energy IP Status The International patent application PCT/GB2012/052550 covering this technology is published as WO2013/061028. National phase patent applications are being pursued in the USA and EU.