Quantum Dot Enhanced Rugate Filtering and Light Trapping

S. Shepard, J. Copeland
Louisiana Tech University, US

Keywords: light-trapping, photovoltaics


Rugate filters use an exponential sinusoidal index profile, which is also multiplied by a window function to further reduce side lobes in comparison to other (discrete index) interference filters. These also have negligible harmonics and typically utilize low index materials resulting in greater angle sensitivity. This results in improved light-trapping for concentrated photovoltaic applications. A limitation of the standard implementations however is that they all require thicker structures to provide more complex filters and this can diminish the transmission of the desired wavelengths. We explore the possibility of circumventing these limitations by utilizing a transverse array (instead of several layers) of nanoparticles of various size and shape – deposited on (and/or etched into) a glass cover on top of a PV in just a few very thin (submicron) layers. Although discrete (conducting or non-conducting) circles or squares etc., these quantum dots are small with respect to the incident wavelength – thus they produce a continuous (rather than discrete) variation of the effective index of refraction. This continuous variation; in conjunction with their ease of controlled deposition and their small size; make them ideal candidates for the fabrication of next generation Rugate filters. We demonstrate useful light trapping examples.