MRS Spring Meeting Research Articles

Hongyou Fan to present Kavli Lecture at 2015 MRS Spring Meeting

Hongyou Fan to present Kavli Lecture at 2015 MRS Spring Meeting

Bower, Minor, Narayan, Szlufarska, and Ueda to chair 2016 MRS Spring Meeting

Bower, Minor, Narayan, Szlufarska, and Ueda to chair 2016 MRS Spring Meeting

Wide Bandgap Copper Chalcopyrite Materials for Photoelectrochemical Hydrogen Production

Photoelectrochemistry (PEC) is one of the most efficient methods to produce alternative fuels, although the efficiency, cost, and durability of lab-scale systems are currently not at the level required to make this technology economically feasible. The chalcopyrite material class, typically identified by its most popular alloy Cu(In,Ga)Se2, provides exceptionally good candidates to meet the requirements identified for cheap, sustainable solar fuels production. As we recently reported[1], co-evaporated 1.6 eV CuGaSe2 offers very high-saturated photocurrent densities (-16 mA.cm- 2 in 0.5M H2SO4 under AM1.5G illumination), long durability (up to 400 hours), and high Faradaic efficiency (>85% for non-catalyzed systems). Although CuGaSe2 has the highest bandgap of the copper chalcopyrite class, its optical characteristics are still too close to that of amorphous silicon (a-Si), a low-cost material our research team has identified as an ideal photovoltaic driverin a monolithic hybrid photoelectrode device. Nevertheless, a solar-to-hydrogen efficiency of 3.7% was achieved using a co-planar integration scheme. In order to improve the water-splitting efficiency further, novel chalcopyrite alloys with bandgap greater than 1.6 eV must be developed.In the present communication, we report on our efforts to synthesize 1.8-2.2 eV band-gap chalcopyrite materials for PEC water splitting. Specifically, we investigated the effect of sulfur on the optical and photoelectrochemical characteristics of the copper chalcopyrite material class. Using co-evaporated 1 μm-thick CuGaSe2 as baseline system, we demonstrate that the substitution of selenium with sulfur is accomplished through a simple annealing step. As a result, a dramatic change in optical properties was observed, with a bandgap increase from 1.6 eV (CuGaSe2) to 2.4 eV (CuGaS2), in good agreement with theoretical predictions[2]. Then, by simply adjusting the indium content in the film during the initial growth process, the bandgap of sulfurized copper chalcopyrite was decreased from 2.4 eV [GGI=Ga/(Ga+In)=1] to 2.2 eV (GGI»0.8) and finally to 2.0 eV (GGI»0.7). X-ray diffraction data indicated successful bulk sulfurization by the shift of the prominent (112), (220), and (312) reflections to higher angles. Preliminary PEC analyses revealed an anodic shift of the flatband potential with increasing bandgap when compared to CuGaSe2. This suggests that the bandgap modification in sulfurized films primarily stems from a downward shift of the valence band, an ideal situation for p-type PEC systems. Saturated photocurrent densities greater than -5 mA/cm2 were achieved with 2.0 eV red CuIn0.3Ga0.7S2 photocathodes in 0.5M H2SO4 under AM1.5G simulated illumination.[1] N. Gaillard, D. Prasher, J. Kaneshiro, S. Mallory, and M. Chong, MRS Spring Meeting, Z2.07 (2013).[2] M. Bär, W. Bohne, J. Rohrich, E. Strub et al., Appl. Phys. Lett. 96, 3857 (2004).

Materials pushing solar

Rapid developments in perovskite solar cells, photocatalysis and transparent conductors were showcased at the 2014 MRS Spring Meeting.

High-Capacity Characteristics of Li-S Rechargeable Battery Using CNT Electrode

Carbon nanotubes (CNTs) are good electronic conductors and have a high chemical stability. We have synthesized vertically aligned CNTs directly on nickel foils and applied them to a cathode of a lithium-sulfur (Li-S) rechargeable battery [1, 2]. The CNTs grown by our thermal CVD process have characteristically a spiral structure. CNT/S composite cathodes were fabricated by impregnating the CNT films with molten S. Figure 1 shows cycle performance and Columbic efficiency of the CNT/S composite cathode containing 8 mg cm-2 with S content of 86 wt% in a 2032 type cell. LiTFSI (0.86 M) dissolved in DME/DOL (9:1 vol %) with LiNO3 (3 wt%) additives was used as electrolyte. The high S loading cell retained a specific capacity of 1000 mAh g-1 even after 50 cycles. This good performance is considered to be attributed by the spiral CNT structure which can hold the electrolyte containing the dissolved polysulfides with a little loss.Reference[1] T. Nozue, presented at the 2012 MRS Spring Meeting, San Francisco, 2012 (unpublished)[2] T. Nozue, presented at The 54th Battery Symposium, Osaka, 2013 (unpublished)

Bandgap Optimization of Copper Indium Gallium Disulfide Chalcopyrites for Solar-Assisted Water Splitting

Photoelectrochemistry (PEC) is an attractive method for producing hydrogen as an alternative fuel to oil. Limitations arising from device efficiencies, cost, and durability demonstrated in laboratories prevent the implementation of this technology on a larger scale. The chalcopyrite material class, exemplified by its most popular alloy Cu(In,Ga)Se2, encompasses some of the most promising candidates to meet the criteria for cheap, sustainable solar fuel production. As we recently reported[i], co-evaporated 1.6 eV CuGaSe2 offers very high-saturated photocurrent densities (20 mA.cm- 2 in pH 0 under AM1.5G illumination), long durability (up to 400 hours), and relatively high Faradaic efficiency (>85% for non-catalyzed systems). Although CuGaSe2 has the highest bandgap of the copper chalcopyrite class, its optical characteristics are still too close to that of amorphous silicon (a-Si), a low-cost material our research team has identified as an ideal photovoltaic driver in a monolithic hybrid photoelectrode device. Nevertheless, a solar-to-hydrogen efficiency of 3.7% was achieved using a co-planar integration scheme, where CuGaSe2 was connected in series with three a-Si solar cells. In order to increase the water-splitting efficiency, novel chalcopyrite alloys with bandgaps greater than 1.6 eV must be developed.In the present communication, we report on our efforts to synthesize 1.8-2.2 eV band-gap chalcopyrite materials for PEC water splitting. Specifically, we investigated the effect of sulfur on the optical and photoelectrochemical characteristics of the copper chalcopyrite material class. Using co-evaporated 1 μm-thick CuGaSe2 as baseline system, we demonstrate that the substitution of selenium with sulfur is accomplished through a simple annealing step. As a result, a dramatic change in optical properties was observed, with a bandgap increase from 1.6 eV (CuGaSe2) to 2.4 eV (CuGaS2), in good agreement with theoretical predictions[ii]. Then, by simply adjusting the indium content in the film during the initial growth process, the bandgap of sulfurized copper chalcopyrite was decreased from 2.4 eV [GGI=Ga/(Ga+In)=1] to 2.2 eV (GGI»0.8) and finally to 2.0 eV (GGI»0.7), as presented in Fig. 1. X-ray diffraction data (Fig. 2) indicated successful bulk sulfurization by the shift of the prominent (112), (220), and (312) reflections to higher angles. Preliminary PEC analyses revealed an anodic shift of the flatband potential with increasing bandgap, when compared to CuGaSe2. This suggests that the bandgap modification in sulfurized films primarily stems from a downward shift of the valence band, an ideal situation for p-type PEC systems. Saturated photocurrent densities greater than -5 mA/cm2 were achieved with 2.0 eV red CuIn0.3Ga0.7S2 photocathodes in 0.5M H2SO4 under AM1.5G simulated illumination.[i] N. Gaillard, D. Prasher, J. Kaneshiro, S. Mallory, and M. Chong, MRS Spring Meeting, Z2.07 (2013).[ii] M. Bär, W. Bohne, J. Rohrich, E. Strub et al., Appl. Phys. Lett. 96, 3857 (2004).

Yury Gogotsi to present Kavli Lecture on nanoscience at 2014 MRS Spring Meeting

Yury Gogotsi to present Kavli Lecture on nanoscience at 2014 MRS Spring Meeting

John J. Tracy of Boeing to give plenary address at 2014 MRS Spring Meeting

John J. Tracy of Boeing to give plenary address at 2014 MRS Spring Meeting

Arun Majumdar of Google to give plenary address on sustainable energy at 2013 MRS Spring Meeting

Arun Majumdar of Google to give plenary address on sustainable energy at 2013 MRS Spring Meeting

Younan Xia to present Kavli Lecture on nanoscience at 2013 MRS Spring Meeting

Younan Xia to present Kavli Lecture on nanoscience at 2013 MRS Spring Meeting

Brongersma, Matias, Segalman, Shea, and Watanabe to chair 2013 MRS Spring Meeting

Brongersma, Matias, Segalman, Shea, and Watanabe to chair 2013 MRS Spring Meeting

John Pendry to give plenary address on metamaterials at 2012 MRS Spring Meeting

John Pendry to give plenary address on metamaterials at 2012 MRS Spring Meeting

Thomas P. Russell to present Kavli lecture on nanoscience at 2012 MRS Spring Meeting

Thomas P. Russell to present Kavli lecture on nanoscience at 2012 MRS Spring Meeting

Characterization and nanopatterning of organically functionalized graphene with ultrahigh vacuum scanning tunneling microscopy

Abstract

Estroff, Liu, Nielsch, and Wada to chair 2012 MRS Spring Meeting

Estroff, Liu, Nielsch, and Wada to chair 2012 MRS Spring Meeting

Yet-Ming Chiang to give plenary address at 2011 MRS Spring Meeting

Yet-Ming Chiang to give plenary address at 2011 MRS Spring Meeting

Xiang Zhang to present Kavli Lecture at 2011 MRS Spring Meeting

Xiang Zhang to present Kavli Lecture at 2011 MRS Spring Meeting

2010 MRS Spring Meeting Reveals Integration of Various Materials Developments

2010 MRS Spring Meeting Reveals Integration of Various Materials Developments

Chen, Eom, Mao, and O'Hayre to Chair 2011 MRS Spring Meeting

Chen, Eom, Mao, and O'Hayre to Chair 2011 MRS Spring Meeting

A fully integrated optical detector with a‐Si:H based color photodiodes

AbstractThe fabrication of an electrophoresis separation microchip with monolithic integrated excitation light source and variospectral photodiodes for absorption detection is presented in this paper. Microchip based separation techniques are essential elements in the development of fully integrated micro‐total analysis systems (µ‐TAS). An integrated microfluidic device, like an application specific lab‐on‐microchip (ALM) (Seibel et al., in: MRS Spring Meeting, San Francisco, USA, 2005 1), includes all components, necessary to perform a chemical analysis on chip and it can be used as a stand‐alone unit directly at the point of sampling. Variospectral diodes based on hydrogenated amorphous silicon (a‐Si:H) technology allow for advanced optical detection schemes, because the spectral sensitivity of the devices can be tailored to fit the emission of specific fluorescent markers. Important features of a‐Si:H variospectral photodiodes are a high dynamic range, a bias‐tunable spectral sensitivity and a very good linearity for the separation of mixed color signals.magnified image Principle of ALM device