Browsing by Author "Sun, X."
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Item Open Access Anisotropic stimulated emission from aligned CdSe/CdS dot-in-rods(IEEE, 2014-10) Gao, Y.; Ta, V. D.; Zhao, X.; Wang, Y.; Chen, R.; Zhao, Y.; Dang, C.; Sun, X.; Sun, H.; Demir, Hilmi VolkanAnisotropic optical properties of CdSe/CdS dot-in-rods loaded in a capillary tube are demonstrated, suggesting nanorods' alignment with a microfluidic approach. Polarized emissions from photoluminescence and whispering gallery mode lasing show promising applications for lighting and displays. © 2014 IEEE.Item Open Access Decompositional analysis of Kronecker structured Markov chains(Kent State University, 2008) Bao, Y.; Bozkur, I. N.; Dayar, T.; Sun, X.; Trivedi, K. S.This contribution proposes a decompositional iterative method with low memory requirements for the steadystate analysis ofKronecker structured Markov chains. The Markovian system is formed by a composition of subsystems using the Kronecker sum operator for local transitions and the Kronecker product operator for synchronized transitions. Even though the interactions among subsystems, which are captured by synchronized transitions, need not be weak, numerical experiments indicate that the solver benefits considerably from weak interactions among subsystems, and is to be recommended specifically in this case. © 2008, Kent State University.Item Open Access Demonstration of the portability of porous microstructure architecture to indium-doped ZnO electron selective layer for enhanced light scattering in inverted organic photovoltaics(Springer New York LLC, 2016) Nirmal A.; Kyaw A.K.K.; Sun, X.; Demir, Hilmi VolkanWe propose and demonstrate the incorporation of porous microstructures on indium-doped zinc oxide (IZO) electron selective layer in inverted organic photovoltaics (OPV). Porosity was induced in the IZO layer with the addition of polyethylene glycol (PEG) organic template at the optimal IZO/PEG ratio of 4:1. When compared to the OPV device with non-porous IZO, the device employing porous IZO showed a 16 % improvement in current density and a 13 % improvement in efficiency. This is primarily due to the increased light scattering as substantiated by the haze factor studies. This PEG assisted method of introducing microporous structure is therefore shown to be compatible with the doped interlayer and is thus a portable method of enhancing light scattering in OPV devices.Item Open Access Escaping local optima in a class of multi-agent distributed optimization problems: a boosting function approach(IEEE, 2014) Sun, X.; Cassandras, C. G.; Gökbayrak, KaanWe address the problem of multiple local optima commonly arising in optimization problems for multi-agent systems, where objective functions are nonlinear and nonconvex. For the class of coverage control problems, we propose a systematic approach for escaping a local optimum, rather than randomly perturbing controllable variables away from it. We show that the objective function for these problems can be decomposed to facilitate the evaluation of the local partial derivative of each node in the system and to provide insights into its structure. This structure is exploited by defining 'boosting functions' applied to the aforementioned local partial derivative at an equilibrium point where its value is zero so as to transform it in a way that induces nodes to explore poorly covered areas of the mission space until a new equilibrium point is reached. The proposed boosting process ensures that, at its conclusion, the objective function is no worse than its pre-boosting value. However, the global optima cannot be guaranteed. We define three families of boosting functions with different properties and provide simulation results illustrating how this approach improves the solutions obtained for this class of distributed optimization problems.Item Open Access High-efficiency light-emitting diodes of organometal halide perovskite amorphous nanoparticles(American Chemical Society, 2016) Xing, J.; Yan, F.; Zhao Y.; Chen, S.; Yu, H.; Zhang, Q.; Zeng, R.; Demir, Hilmi Volkan; Sun, X.; Huan, A.; Xiong, Q.Organometal halide perovskite has recently emerged as a very promising family of materials with augmented performance in electronic and optoelectronic applications including photovoltaic devices, photodetectors, and light-emitting diodes. Herein, we propose and demonstrate facile solution synthesis of a series of colloidal organometal halide perovskite CH3NH3PbX3 (X = halides) nanoparticles with amorphous structure, which exhibit high quantum yield and tunable emission from ultraviolet to near-infrared. The growth mechanism and photoluminescence properties of the perovskite amorphous nanoparticles were studied in detail. A high-efficiency green-light-emitting diode based on amorphous CH3NH3PbBr3 nanoparticles was demonstrated. The perovskite amorphous nanoparticle-based light-emitting diode shows a maximum luminous efficiency of 11.49 cd/A, a power efficiency of 7.84 lm/W, and an external quantum efficiency of 3.8%, which is 3.5 times higher than that of the best colloidal perovskite quantum-dot-based light-emitting diodes previously reported. Our findings indicate the great potential of colloidal perovskite amorphous nanoparticles in light-emitting devices. © 2016 American Chemical Society.Item Open Access Light trapping in inverted organic photovoltaics with nanoimprinted ZnO photonic crystals(IEEE Electron Devices Society, 2017) Nirmal A.; Kyaw A.K.K.; Jianxiong, W.; Dev K.; Sun, X.; Demir, Hilmi VolkanZinc oxide photonic crystal (ZnO PC) formed via facile nanoimprinting was employed on the ZnO electron selective layer of inverted organic photovoltaics (OPV). Optimized inverted OPV fabricated with these highly ordered periodic structures provided effective light trapping, which resulted in increased incident light absorption in the active layer. Consequently, OPVs with the ZnO PC layers show a 23% current density improvement compared with OPVs with planar ZnO layer. Finite-difference time-domain simulation studies show that the electric field intensity is significantly higher in the active layer for devices with ZnO PC structures in comparison with reference devices with planar ZnO electron selective layer. Nanoimprinted ZnO PC is, thus, a viable method for light absorption and efficiency enhancement in OPVs. � 2011-2012 IEEE.