We have deposited textured ZnO:Al films over large areas using a reactive-environment hollow cathode sputtering (RE-HCS) system developed in house, and have achieved excellent carrier mobilities (up to 49.5 cm 2 /Vs at a carrier concentration of 4.42 x 10 20 /cm 3 ). Both the electrical properties and optical properties (total transmission and haze) are superior to those exhibited by commercially available SnO 2 :F. Using these textured ZnO:Al films, we have achieved an a-Si:H solar cell efficiency boost of 8% relative to commercial SnO 2 :F superstrates which resulted from improvements in all three PV parameters, namely V oc , J sc , and FF. We have also determined the dependence of cell performance on the degree of haze in the ZnO:Al films. Electrical, physical, and optical properties of ZnO:Al and SnO 2 :F, as determined by four-point probe, Hall effect, SEM, AFM, ICP, transmission (total and diffuse), and work function measurements are presented and correlated to the observed differences in a-Si solar cell performance. We have also developed a refractive index matching layer that, when inserted between the TCO and the a-Si:H layers, resulted in an increase in J sc of 3%. Finally, we present some experiments on the effect of TCO type on nc-Si:H solar cell performance. From these experiments, we confirmed that SnO 2 :F by itself is not a suitable TCO for nc-Si:H cells, but found that SnO 2 :F overcoated with TiO 2 followed by ZnO was the most effective superstrate for this type of cell.

The ability to control the light-matter interaction with an external stimulus is a very active area of research since it creates exciting new opportunities for designing optoelectronic devices. Recently, plasmonic metasurfaces have proven to be suitable candidates for achieving a strong light-matter interaction with various types of optical transitions, including intersubband transitions (ISTs) in semiconductor quantum wells (QWs). For voltage modulation of the light-matter interaction, plasmonic metasurfaces coupled to ISTs offer unique advantages since the parameters determining the strength of the interaction can be independently engineered. In this work, we report a proof-of-concept demonstration of a new approach to voltage-tune the coupling between ISTs in QWs and a plasmonic metasurface. In contrast to previous approaches, the IST strength is here modified via control of the electron populations in QWs located in the near field of the metasurface. By turning on and off the ISTs in the semiconductor QWs, we observe a modulation of the optical response of the IST coupled metasurface due to modulation of the coupled light-matter states. Because of the electrostatic design, our device exhibits an extremely low leakage current of ∼6 pA at a maximum operating bias of +1 V and therefore very low power dissipation. Our approach provides a new direction for designing voltage-tunable metasurface-based optical modulators.

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Carbon capture and sequestration (CCS) may play a key role in our energy future. However, the widespread sequestration of CO 2 into storage reservoirs is inhibited by safety and leakage concerns. Effective leakage monitoring at the surface is recently made possible by the development of quantum cascade (QC) laser-based sensors, which are capable of tracking fluxes in CO 2 isotope concentrations. In this paper, we initially discuss the status of this technology, including recent results from distributed feedback QC lasers for use in sensing CO 2 isotopic ratios. These lasers show single-mode emission at 4.32 µm, overlapping strong absorption resonances of 12 CO 2 , 13 CO 2 , and 18 OCO. We then consider the value of such devices for quantifying CO 2 leakage using a climate-economy integrated-assessment model that is modified to include CCS. The sensitivity of model outcomes to reservoir leakage is studied, showing that an average reservoir storage half-life on the order of 1000 years or longer can limit atmospheric temperature increases to 2°C or less over the next 150 years for economically optimal emissions scenarios. The present day economic value of CCS is established versus reservoir half-life, showing a significant return on investment (∼2 trillion U.S.$, or ∼4% of gross world product) when the average reservoir half-life is 250 years, with a sharp drop in the value of CCS technology for half-life values below 250 years. Quantifying CO 2 leakage rates via QC laser-based sensing will contribute greatly toward accurately assessing CCS technology and its efficacy as part of CO 2 limitation strategies.Index Terms-Environmental economics, laser applications, quantum cascade lasers, trace gas sensing.