  We design a multi-layered solar spectral splitting planar concentrator for
near infrared (NIR) light energy harvesting application. Each layer includes a
silicon nitride based subwavelength diffraction grating on top of a glass
substrate that is optimized to diffract the incoming solar radiation in a
specific band from a broad spectral band (700-1400 nm in the NIR region) into
guided modes propagating inside the glass substrate. The steep diffraction
angle due to subwavelength grating results in concentrated light at the edge of
each layer where it is then converted to electricity using a photovoltaic cell.
The spectral splitting planar concentrator shows an overall NIR guiding
efficiency of ~18%, and power conversion efficiency of ~11%. The design can be
potentially used for building integrated photovoltaics application.
