Graded-Index Fluoropolymer Antireflection Coatings for Invisible Plastic Optics.

Plastic optics are used in an ever-expanding range of applications and yet a durable, high performance antireflection (AR) coating remains elusive for this material class. Here, we introduce a sacrificial porogen approach to produce ultralow refractive index nanoporous fluoropolymer AR coatings via thermal coevaporation of Teflon AF and the small molecule N, N'-bis(3-methylphenyl)- N, N'-diphenylbenzidine (NPD). Using this approach, we demonstrate a five-layer, step-graded AR coating that reduces the solar spectrum-averaged (400 < λ < 2000 nm) reflectance of acrylic plastic to <0.

Hybrid perovskite light emitting diodes under intense electrical excitation.

Hybrid perovskite semiconductors represent a promising platform for color-tunable light emitting diodes (LEDs) and lasers; however, the behavior of these materials under the intense electrical excitation required for electrically-pumped lasing remains unexplored. Here, we investigate methylammonium lead iodide-based perovskite LEDs under short pulsed drive at current densities up to 620 A cm. At low current density (J < 10 A cm), we find that the external quantum efficiency (EQE) depends strongly on the time-averaged history of the pulse train and show that this curiosity is associated with slow ion movement that changes the internal field distribution and trap density in the device.

Fundamental and practical limits of planar tracking solar concentrators.

Planar microtracking provides an alternate paradigm for solar concentration that offers the possibility of realizing high-efficiency embedded concentrating photovoltaic systems in the form factor of standard photovoltaic panels. Here, we investigate the thermodynamic limit of planar tracking optical concentrators and establish that they can, in principal, achieve the sine limit of their orientationally-tracked counterparts provided that the receiver translates a minimum distance set by the field of view half-angle. We develop a phase space methodology to optimize practical planar tracking concentrators and apply it to the design of a two surface, catadioptric system that operates with > 90% optical efficiency over a 140° field of view at geometric gains exceeding 1000×.

Wide-angle planar microtracking for quasi-static microcell concentrating photovoltaics.

Concentrating photovoltaics offer a way to lower the cost of solar power. However, the existing paradigm based on precise orientation of large-area concentrator modules towards the Sun limits their deployment to large, open land areas. Here, we explore an alternate approach using high-efficiency microcell photovoltaics embedded between a pair of plastic lenslet arrays to demonstrate quasi-static concentrating photovoltaic panels <1 cm thick that accomplish full-day tracking with >200x flux concentration ratio through small (<1 cm) lateral translation at fixed latitude tilt.