Waveguiding properties of surface states in photonic crystals

We propose and analyze novel surface-state-based waveguides in bandgap photonic crystals. We discuss surface mode band structure, field localization and effect of imperfections on the waveguiding properties of the surface modes. We demonstrate that surface-state-based waveguides can be used to achieve directional emission out of the waveguide. We also discuss the application of the surface-state waveguides as efficient light couplers for conventional photonic crystal waveguides.Comment: 4 pages 5 figure

A General Design Rule to Manipulate Photocarrier Transport Path in Solar Cells and Its Realization by the Plasmonic-Electrical Effect

It is well known that transport paths of photocarriers (electrons and holes) before collected by electrodes strongly affect bulk recombination and thus electrical properties of solar cells, including open-circuit voltage and fill factor. For boosting device performance, a general design rule, tailored to arbitrary electron to hole mobility ratio, is proposed to decide the transport paths of photocarriers. Due to a unique ability to localize and concentrate light, plasmonics is explored to manipulate photocarrier transport through spatially redistributing light absorption at the active layer of devices. Without changing the active materials, we conceive a plasmonic-electrical concept, which tunes electrical properties of solar cells via the plasmon-modified optical field distribution, to realize the design rule. Incorporating spectrally and spatially configurable metallic nanostructures, thin-film solar cells are theoretically modelled and experimentally fabricated to validate the design rule and verify the plasmonic-tunable electrical properties. The general design rule, together with the plasmonic-electrical effect, contributes to the evolution of emerging photovoltaics.published_or_final_versio

New concept to break the intrinsic properties of organic semiconductors for optical sensing applications

Invited paper - Session 9: Radiation-to-Current Transducers: Engineering Materials to Increase Current Generation - no. 9608-44The space charge limit (SCL) effect is a universal phenomenon in semiconductor devices involving light emitting diodes, solar cells, and photodetectors. Typically, the SCL will exist in the condition of (1) unbalanced hole and electron mobility; (2) thick active layer; (3) high light intensity or dense photocarriers (electrons and holes) generation; and (4) moderate reverse bias. Through the study of plasmonic organic solar cells, we will show metallic nanostructures go beyond their optical functions to control recombination, transport, and collection of photocarriers generated from active organic materials. Through spatially redistributing light absorption at the active layer, the proposed plasmonic-electrical concept is fundamentally different from the hot carrier effect where photocarriers are generated from metallic nanostructures. The new plasmonic-electrical effect not only lays a physical foundation but also upgrades electrical properties for semiconductor devices [1]. We will also design different device structures to investigate and demonstrated how plasmonic-electrical [2] and plasmonic-optical [3] effects can be used to enhance device performances such as improving the light absorption of solar cells, increasing emission efficiency of light emitting devices, reducing dark current and enhancing sensitivity of photodetector as well as intensifying the surface enhanced Raman scattering for biosensor applications. Besides the optical (plasmonic) resonances from metal nanostructure, we will also use metal nanostructures to demonstrate electrical resonance which can be used for bistable and memory devices [4]. Consequently, exploiting both plasmonic-optical and plasmonic-electrical effects via metallic nanostructures will open up a more flexible and integrated way to design high-performance optoelectronic nanodevices. [1] W.E.I. Sha, X. Li, W.C.H. Choy, Scientific Reports, vol. 4, p. 6236 (10pp), 2014. [2] F.X. Xie, W.C.H. Choy, W.E.I. Sha, D. Zhang, S. Zhang, X. Li, C.W. Leung, J. Hou, Energy Environ. Sci., vol. 6, pp.3372 – 3379, 2013; D. Zhang, W.C.H. Choy, F. Xie, W.E.I. Sha, X. Li, B. Ding, K. Zhang, F. Huang, and Y. Cao, Adv. Funct. Mat., vol. 23, pp.4255–4261, 2013; D.D.S. Fung, L. Qiao, W.C.H. Choy, C.C.D. Wang, W.E.I. Sha, F. Xie, and S. He, J. Mater. Chem., vol. 21, pp. 16349 – 16356, 2011. [3] X.H. Li, W.C. H. Choy, X. Ren, D. Zhang, H.F. Lu, Adv. Funct. Mat. DOI: 10.1002/adfm.201303384; X.H.Li, W.C.H.Choy, H.F. Lu, W.E.I. Sha, and H. P. Ho, Adv. Funct. Mat., vol.23, pp.2728–2735, 2013; X.H. Li, W. C.H. Choy, L Huo, F.X. Xie, W.E.I. Sha, B. Ding, X. Guo, Y. Li, J. Hou, J. You, Y. Yang, Adv. Mater. vol. 24, pp.3046-3052, 2012; X.H. Li, W. E.I. Sha, W.C.H. Choy, D.D.S. Fung, F. X. Xie, J. of Phys. Chem. C, vol. 116, pp.7200-7206, 2012; C.C.D. Wang, W. C. H. Choy, C. Duan, D.D.S. Fung, W.E.I. Sha, F.X. Xie, F. Huang, and Y. Cao, J. Mater. Chem., vol. 22, pp.1206–1211, 2012. [4] T.H. Zheng, W.C.H. Choy, and Y.X. Sun, vol. 19, pp.2648-2653, 2009; T.H. Zheng, W.C.H. Choy, and Y.X. Sun, Appl. Phys. Lett, vol. 94, 123303 (pp.3), 2009.published_or_final_versio

A simulation assessment of the height of light shelves to enhance daylighting quality in tropical office buildings under overcast sky conditions in Dhaka, Bangladesh

The objective of this paper is to highlight the effectiveness of light shelves in tropical office buildings to enhance interior daylighting quality. Daylight simulation was performed for custom light shelves for a typical office floor of Dhaka City in Bangladesh, to determine the best possible location under overcast sky conditions. Six alternative models of a 3m high study space were created with varying heights of light shelves. The 3D models were first generated in the Ecotect to study the distribution and uniformity of daylight in the interior space with split- flux method. These models were then exported to a physically-based backward raytracer, Radiance Synthetic Imaging software to generate realistic lighting levels for validating and crosschecking the Ecotect results. The results showed that for achieving light levels closest to specified standards, light shelves at a height of 2m above floor level perform better among the seven alternatives studied including the alternative where no light shelves are present. Finally, the decisions were verified with DAYSIM simulation program to ensure the compliance of the decisions with dynamic annual climate-based daylight performance metrics

Nearby Supernova Factory Observations of SN 2007if: First Total Mass Measurement of a Super-Chandrasekhar-Mass Progenitor

We present photometric and spectroscopic observations of SN 2007if, an overluminous (M_V = -20.4), red (B-V = 0.16 at B-band maximum), slow-rising (t_rise = 24 days) type Ia supernova in a very faint (M_g = -14.10) host galaxy. A spectrum at 5 days past B-band maximum light is a direct match to the super-Chandrasekhar-mass candidate SN Ia 2003fg, showing Si II and C II at ~9000 km/s. A high signal-to-noise co-addition of the SN spectral time series reveals no Na I D absorption, suggesting negligible reddening in the host galaxy, and the late-time color evolution has the same slope as the Lira relation for normal SNe Ia. The ejecta appear to be well mixed, with no strong maximum in I-band and a diversity of iron-peak lines appearing in near-maximum-light spectra. SN2007 if also displays a plateau in the Si II velocity extending as late as +10 days, which we interpret as evidence for an overdense shell in the SN ejecta. We calculate the bolometric light curve of the SN and use it and the \ion{Si}{2} velocity evolution to constrain the mass of the shell and the underlying SN ejecta, and demonstrate that SN2007 if is strongly inconsistent with a Chandrasekhar-mass scenario. Within the context of a "tamped detonation" model appropriate for double-degenerate mergers, and assuming no host extinction, we estimate the total mass of the system to be 2.4 +/- 0.2 solar masses, with 1.6 +/- 0.1 solar masses of nickel-56 and with 0.3-0.5 solar masses in the form of an envelope of unburned carbon/oxygen. Our modeling demonstrates that the kinematics of shell entrainment provide a more efficient mechanism than incomplete nuclear burning for producing the low velocities typical of super-Chandrasekhar-mass SNeIa.Comment: 23 pages, 13 figures, 4 tables, emulateapj format; v2 fixed some typos and added a reference; v3 included minor copy-editing changes + fixed typos in Figure 9, Table 4; accepted to Ap

Analysis of wavefront data obtained with a pyramidal sensor in pseudophakic eyes implanted with diffractive intraocular lenses

Purpose: To investigate the clinical validity of using wavefront measurements obtained with a recently available pyramidal aberrometer to assess the optical quality of eyes implanted with diffractive intraocular lenses (IOLs). Methods: Individual biometric data were used to create models of pseudophakic eyes implanted with two diffractive IOLs. Their synthetic wavefronts were calculated by ray-tracing with near infrared wavelength (0.85 μm). Comparisons of the through-focus visual acuity of 12 pseudophakic eyes were obtained with three different methods: clinical defocus curves; simulated defocus curves calculated from ray-tracing in the customized model eyes; and through-focus simulated defocus curves calculated from the wavefront data measured with a pyramidal aberrometer. Results: Image quality calculated from wavefront data obtained by ray-tracing with 0.85 μm wavelength, without scaling the phase to 0.55 μm, resulted in a significantly different through-focus curve compared to the reference values. Even so, after scaling of the wavefront data to 0.55 μm, the defocus curves calculated from the wavefronts measured with the pyramidal aberrometer did not match the shape and the depth of field of the clinical defocus curves or the theoretical expected values. Conclusions: Correcting for the longitudinal chromatic aberration of the eye when measuring the wavefront of eyes implanted with diffractive IOLs under near infrared light only accounts for the best focus shift due to the longitudinal chromatic aberration, but not for the wavelength dependence of the diffractive element. The pyramidal sensor does not seem to properly sample the slopes of a wavefront measured from a pseudophakic eye implanted with a presbyopia-correcting diffractive IOL to a clinically acceptable level.Acknowledgments: The authors thank CSO for providing the Osiris-T during the study and Pete Kollbaum and Matt Jaskulski from Indiana University for sharing the Matlab code used to parse the Osiris .wfm files

Breaking the Space Charge Limit in Organic Solar Cells by a Novel Plasmonic-Electrical Concept

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