ABSTRACT
The challenge in solar energy today is not the cost of photovoltaic (PV) electricity generation, already competing with fossil fuel prices, but rather utility-scale energy storage and flexibility in supply. Low-cost thermal energy storage (TES) exists but relies on expensive heat engines. Here, we introduce the concept of luminescent solar power (LSP), where sunlight is absorbed in a photoluminescent (PL) absorber, followed by red-shifted PL emission matched to an adjacent PV cell's band edge. This way the PV cell operates nearly as efficiently as under direct illumination but with minimal excessive heat. The PL absorber temperature rises because of thermalization, allowing it to store the excessive heat, which can later be converted into electricity. Tailored luminescent materials that support an additional 1.5 kW h PV electricity for every 1 kW h of (virtual) heat engine electricity with a dynamic shift between the two sources are experimentally demonstrated. Such an ideal hybrid system may lead to a potential reduction in the cost of electricity for a base-load solution.
ABSTRACT
The maximal Shockley-Queisser efficiency limit of 41% for single-junction photovoltaics is primarily caused by heat dissipation following energetic-photon absorption. Solar-thermophotovoltaics concepts attempt to harvest this heat loss, but the required high temperatures (T>2,000 K) hinder device realization. Conversely, we have recently demonstrated how thermally enhanced photoluminescence is an efficient optical heat-pump that operates in comparably low temperatures. Here we theoretically and experimentally demonstrate such a thermally enhanced photoluminescence based solar-energy converter. Here heat is harvested by a low bandgap photoluminescent absorber that emits thermally enhanced photoluminescence towards a higher bandgap photovoltaic cell, resulting in a maximum theoretical efficiency of 70% at a temperature of 1,140 K. We experimentally demonstrate the key feature of sub-bandgap photon thermal upconversion with an efficiency of 1.4% at only 600 K. Experiments on white light excitation of a tailored Cr:Nd:Yb glass absorber suggest that conversion efficiencies as high as 48% at 1,500 K are in reach.
ABSTRACT
Line illumination geometries have advantageous properties for temporal focusing nonlinear microscopy. The characteristics of line temporal focusing (LITEF) in transparent and scattering media are studied here both experimentally and using numerical model simulations. We introduce an approximate analytical formula for the dependence of axial sectioning on the laser and microscope's parameters. Furthermore, we show that LITEF is more robust to tissue scattering than wide-field temporal focusing, and can penetrate much deeper into scattering tissue while maintaining good sectioning capabilities. Based on these observations, we propose a new design for LITEF-based tissue imaging at depths that could potentially exceed the out-of-focus physical excitation limit.
