PacSurf2014 Session EH-TuP: Energy Harvesting & Storage Poster Session

The brilliant color reflected from nature stems from a photonic crystal morphology. There are many examples in biology of the manipulation of sunlight by nanoscale features including such diverse applications as temperature control, mate attraction, antireflection, and the efficient collection of low light levels. In particular, the striking “structural black” —an absence of reflected visible light—of butterfly scales suggests that biomimicry might be a viable route to enhanced optolectronic devices. Here we describe a materials-agnostic, 2-D, photonic crystal morphology that enhances the efficiency of optoelectronic devices. The morphology is developed by patterning the organic photoactive material via fluorine chemistry, a method that lends itself to large area fabrication of photonic crystal nanostructures. The photonic crystal cell morphology increases photocurrents generally, and particularly through the excitation of resonant modes near the band edge of the organic photovoltaic material. The device performance of the photonic crystal cell showed a nearly doubled increase in efficiency relative to conventional planar cell designs. Photonic crystals can also enhance performance of other optoelectronic devices including organic laser.

Beryllium intermetallic compounds have shown a variety of excellent properties, such as neutron multiplier, refractory function, hydrogen storage, superconductivity and so on. Be₁₂M compounds (M=Ti, V and Zr) have been investigated as neutron multiplier in fields of fusion reactor while Be₁₇M₂ compounds have been focused on refractory materials. In addition, Be₂M have been known as a Laves phase which is characterized by an A₂B type compound performing higher H₂ gas storage potential. Although great interest on hydrogen properties of Be₂M owing to its lower density has been aroused from viewpoints of reactivity with H₂O, trap site of hydrogen and amount of H₂ gas in this compound, few studies on the Be₂M found and its data base is still unsatisfactory.

In this study, we report on preliminary synthesis of Be₂Ti compound and its properties, such as hydrogen generation due to reaction with H₂O and hydrogen storage. Additionally, first principles calculation of hydrogen trap site in this compound was carried out in order to compare to empirical data.

X-ray diffraction profiles and electron probe micro-analysis results clarify that the preliminary synthesis of Be₂Ti was successful by homogenization treatment and plasma sintering. Hydrogen generation rate of the Be₂Ti by a reaction with 1 % H₂O increased as test temperature increased. High temperature exposure with H₂O leads to formation of TiO₂ on the surface. In addition, hydrogen storage result of Be₂Ti evaluated by pressure-concentration-temperature curve depicts that Be₂Ti indicated H₂ gas storage concentration with 1.6 w.t. % at 323 K when the H₂ pressure increases up to 10 MPa. According to the first principle calculation, there were two hydrogen trap sites, tetrahedron and center of triangle with solidus energies of -0.52 and -0.05 eV, respectively, indicating maximum trap site with 5.4 w.t. %.

In this study, we characterized the cyclic performance of an air electrode employing a carbon nanotube (CNT)/Co₃O₄ nanocomposite. The lithium anode and electrolyte were replaced every 50 cycles in order to exclude the effect of a corrupted anode and electrolyte and to determine the “real” cyclic performance of the electrode. The overpotential of the cells increased during the first 50 cycles; however, it almost vanished when the lithium anode and electrolyte were replaced. This result indicates that the increased overpotential of the cells during cycling is highly attributed to the corrupted lithium anode and electrolyte [1, 2]. The cycle life of the cell also significantly increased upon replacement of the lithium anode and electrolyte. This confirms that air electrodes have the ability to maintain their designated capacity (such as 1000 mAh·g_electrode⁻¹) for much longer cycles if the lithium anode and electrolyte can be made more stable. A polydopamine-coated electrode and a LiI-containing electrolyte were introduced and characterized in order to obtain enhanced cyclic performance of the air electrode.

References

[1] P. G. Bruce, M. M. Ottakam Thotiyl, J. Am. Chem. Soc. 135(2013) 494-500

[2] Jun Lu, Yu Lei, Nature Communications DOI:10.1038/ncomms3383

Since the commercialization of lithium ion battery, development of cathode materials with high capacity has been one of the important factors for enhancing the performance of that. Lithium rich compounds are promising cathode materials due to their high capacity for satisfying demand of high-capacity batteries. However, they have several disadvantages to overcome for commercialization such as poor rate capability, low cyclic performance, and low stability. In this study, we prepared nano-sized Li[Li_0.2Ni_0.16Mn_0.56Co_0.08]O₂/carbon composite for enhanced electrochemical performance such as rate capability. A general method to improve the surface electronic conductivity and enhance the rate capability of cathode is carbon coating. The carbon coating by in-situ carbonization from organic precursors has been successfully applied to LiFePO₄. However, it is difficult to apply to Li-rich compounds because they will lose oxygen during carbonization. That is why we introduced composite between cathode and carbon, instead of carbon coating. In this work, super P, a commercial carbon, was composed with nano-sized Li[Li_0.2Ni_0.16Mn_0.56Co_0.08]O₂. Nano-sized powders were synthesized by combustion method using surfactants (HPC and Gelatin) to disperse the granule particles [1-3]. The polydopamine pre-coating layer was used as a binding agent between cathode powder and super P [4-8]. Nano-sized Li[Li_0.2Ni_0.16Mn_0.56Co_0.08]O₂/Super P composite is expected to exhibit improved rate capability because of dispersed nano-sized lithium rich particles and good electronic conductivity attributed to Super P.

References

[1] D. Desai, F. Rinaldi, S. Kothari, S. Paruchuri, D. Li,M. Lai, S. Fung, D. Both, Int. J. Pharm. 308, 40 (2006) [2] M.Y. Mo, C.C. Ye, K. Lai, Z. Huang, L. Zhu, G. Ma, H. Chen, K.S. Hui, Appl. Surf. Sci. 276, 635 (2013)

[3] A.D. Spong, G. Vitins, J.R. Owen, J. Electrochem. Soc. 152, A2376 (2005)

[4] H. Lee, B.P. Lee, P.B. Messersmith, Nature 448 (2007) 338.

In organic photovoltaics (OPVs), there is a competition between the reduction of absorber thickness and the improvement of the probability of carrier collection. To overcome the competition a highly structured interface is highly desirable. However, a solution-based soft-lithography processing resulted in non-uniform structured surfaces. In this report, we proposed and demonstrated a silica-templated soft-lithographical approach for structuring well-defined and controllable transparent ITO layer for enhancing power conversion efficiency (PCE). Also, we focused on the morphological effects of the patterned ITO on optical properties and PCE.

The brief experimental scheme is as follow. First, close-packed PS nanospheres were formed on a cleaned ITO glass substrate by using gas-liquid-solid interfacial self-assembly method and drying for 3days in vacuum desiccator. After that, PS covered ITO glass was etched at 65℃ with TIN etching solution. Finally, PEDOT:PSS, P3HT:PCBM, and Al electrode were gradually deposited.

The morphology, optical, electric, and cell properties are investigated by FE-SEM, AFM, UV-VIS spectrophotometer, Haze measurement, and solar simulator.

In photovoltaic solar cell, CdS thin films are mostly used buffer layer due to their wide direct band gap(~2.42 eV). The CdS buffer layers which form a p-n junction with absorber layer are deposited by using a variety of deposition methods such as chemical bath deposition (CBD), spray pyrolysis, vacuum-evaporation and sputtering. Among these techniques, chemical bath deposition is widely used method due to its advantage such as easy and inexpensive process. However, CBD technique also has some disadvantages including production of toxic liquid waste containing Cd and ammonia and difficulty in application to mass production scale. In addition, CBD method should be done in liquid phase, so that it can oxidize the absorber layer.

To overcome these disadvantages of CBD method and to apply for large scale deposition, sputtering of Zn(O,S) thin films was proposed. Sputtering method of Zn(O,S) films can reduce the liquid wastes and save the deposition time for fast deposition. It enables all processes for solar cells to be carried out by vacuum processes without exposure to air. In addition, Zn(O,S) thin films can replace the CdS which contains a toxic Cd. Generally, Zn(O,S) thin films can be deposited by sputtering with pure ZnS target by adding oxygen or by co-sputtering using ZnO and ZnS targets. ZnS itself has very high band gap about 3.6 eV, so that oxygen should be added to control the band gap. Currently, their electrical and optical properties of the sputtered Zn(O,S) films have not been fully studied yet.