Near-Unity Absorption in Van der Waals Semiconductors for Ultrathin Photovoltaics, Deep Jariwala, Artur R. Davoyan, Giulia Tagliabue, Michelle C. Sherrott, Joeson Wong and Harry A. Atwater (13 May 2016)
Key criteria for high efficiency photovoltaics include achieving high radiative efficiency, maximizing above-bandgap semiconductor absorption, and enabling carrier-selective charge collection at the cell operating point that exploits the full quasi-Fermi level separation for the carriers. High efficiency inorganic photovoltaic materials (e.g., Si, GaAs and GaInP) can achieve these criteria, but thin film photovoltaic absorbers have lacked the ability to fulfill one or more of these criteria, often due to surface and interface recombination effects. In contrast, Van der Waals semiconductors have naturally passivated surfaces with electronically active edges that allows retention of high electronic quality down-to the atomically thin limit and recent reports suggest that Van der Waals semiconductors can achieve the first criterion of high radiative efficiency. Here, we report that the second criteria for high efficiency of near-unity light absorption is possible in extremely thin (< 15 nm) Van der Waals semiconductor structures by coupling to strongly damped optical modes of semiconductor/metal heterostructures. We demonstrate near unity, broadband absorbing photovoltaic devices using sub-15 nm thick transition metal dichalcogenides (TMDCs) as van der Waals semiconductor active layers. Our TMDC devices show a short circuit current density > 10 mA/cm2 at ~ 20 Suns and exhibits spectral response that parallels the spectral absorption over the above bandgap region. Our work addresses one of the key criteria to enable TMDCs to achieve high photovoltaic efficiency.
See also: http://arxiv.org/abs/1605.04255
Engineering and Manipulating Structured Excitons, Xiaoning Zang, Simone Montangero, Lincoln D. Carr and Mark T. Lusk (13 May 2016)
When a semiconductor absorbs light, the resulting electron-hole superposition amounts to a uncontrolled quantum ripple that eventually degenerates into diffusion (Frenkel 1931, Wannier 1937, Lanzani 2012). If the conformation of these excitonic superpositions could be engineered, though, they would constitute a new means of transporting information and energy. We show that properly designed laser pulses can be used to create such structured excitons. They can be formed with a prescribed speed, direction and spectral make-up that allows them to be selectively passed, rejected or even dissociated using superlattices. Their coherence also provides a handle for manipulation using active, external controls. Energy and information can be conveniently processed and subsequently removed at a distant site by reversing the original procedure to produce a stimulated emission. The ability to create, manage and remove structured excitons comprises the foundation for opto-excitonic circuits with application to a wide range of quantum information, energy and light-flow technologies. The paradigm is demonstrated using both tight-binding and Time-Domain Density Functional Theory simulations.
I don’t quite understand what the hold up with this could be.
Commercial capital, or government funding?