Catching Some Rays: A Look at the Present Status and Future Promise of Dye Sensitized Solar Cells

Jason B. Baxter

J. Vac. Sci. Technol. A 30, 020801 (2012);
doi:10.1116/1.3676433

Each day the sun bathes the earth with enough energy to power the entire global community many times over, but we currently capture only a tiny fraction of it. The relatively high cost of the electricity produced by traditional solar panels may be partly to blame for solar energy's bit part. "I think your best bet for expanding the use of solar energy is to make it at least as cheap as fossil fuels," says Professor Jason Baxter, a chemical engineering researcher at Drexel University in Philadelphia who studies solar cells. Baxter is the author of a review paper, recently published in the Journal of Vacuum Science and Technology A, that examines possible ways to improve the price/performance ratio of one promising form of solar energy technology: dye sensitized solar cells.

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The Surprising Importance of Photo-Assisted Etching of Silicon in Chlorine-Containing Plasmas

Hyungjoo Shin, Weiye Zhu, Vincent M. Donnelly, and Demetre J. Economou

J. Vac. Sci. Technol. A 30, 021306 (2012);
doi:10.1116/1.3681285

Using a plasma to etch patterns into silicon wafers is an essential step in many manufacturing processes. Now researchers from the University of Houston, in Texas, have demonstrated for the first time that the photons in chlorinecontaining plasma contribute to the etching process. While the effects of photoassisted etching are relatively small for high-energy plasmas, they become more noticeable at the low energies required for etching nanoscale patterns. The role of photons could help explain some defects, such as sloped sidewalls and microtrenches, that are sometimes found in plasma-etched silicon. Plasmas contain ions, electrons, and photons, and, in most etching applications, ions do the majority of the work to zap away silicon. High-energy ions, however, may wreck unintended damage on the patterned silicon. Lowering the energy of the ions can reduce the damage, and is required to etch fine, nanoscale patterns, but as the ion-etching rate slows, any effects from photo-assisted etching gain relative significance. Read more

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Spatial Atomic Layer Deposition's Assembly Line Debut

Paul Poodt, David C. Cameron, Eric Dickey, Steven M. George, Vladimir Kuznetsov, Gregory N. Parsons, Fred Roozeboom, Ganesh Sundaram, and Ad Vermeer

J. Vac. Sci. Technol. A 30, 010802 (2012);
doi:10.1116/1.3670745

A research boom has landed a relatively new manufacturing technique, called spatial atomic layer deposition (or spatial ALD), a spot on the assembly line. Traditional atomic layer deposition allows researchers to put thin coatings of a material onto a substrate's surface with atomic-level control over the thickness of the material layers. "You can follow the topology of a material exactly" with ALD, says Paul Poodt, senior research scientist at TNO (the Netherlands Organization for Applied Scientific Research)and spatial ALD pioneer. The newer technique has the same quality control, but is several times faster, and it can be incorporated more easily into existing manufacturing processes, expanding the technique's usefulness to a wider range of applications.Read more

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High-efficiency and highly stable a-Si:H solar cells deposited at high rate (8 Å/s) with disilane grading process.

Guofu Hou, Qihua Fan, Xianbo Liao, Changyong Chen, Xianbi Xiang, and Xunming Deng

J. Vac. Sci. Technol. A 29, 061201 (2011);
doi:10.1116/1.3630052

This paper presents our recent results on the high-rate deposition of high-efficiency and highly stable hydrogenated amorphous silicon (a-Si:H) solar cells with all layers deposited by 13.56 MHz radio frequency glow discharge. Using a linear disilane (Si2H6) grading process, high initial active-area efficiency of 11.42% has been obtained for the a-Si:H top cells with an effective i-layer deposition rate of 8 Å/s. It is also found that the light-soaking stability of the a-Si:H top cells is much improved by the Si2H6 grading process with the best a-Si:H top cell exhibiting only 11.2% light-induced degradation after 1000 h of light-soaking. Integrating the high-rate deposited a-Si:H top cell in an amorphous silicon/amorphous silicon germanium (a-Si:H/a-SiGe:H) tandem cell, an initial active-area efficiency of 12.57% is achieved. After light soaking for 1008 h, the stable efficiency is still as high as 11.02%, corresponding to only a 12.31% degradation. To the best of our knowledge, this is the best performance for a-Si:H based solar cells at such a high deposition rate by 13.56 MHz RF-PECVD. Possible mechanisms responsible for the superior stability of the a-Si:H solar cells deposited by the Si2H6 grading process are discussed. Read more

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Plasma-surface reactions and the spinning-wall method

V. M. Donnelly, J. Guha, and L. Stafford

J. Vac. Sci. Technol. A 29, 010801 (2011);
doi:10.1116/1.3517478

Plasma processes enable a wide range of products from integrated circuits that are at the heart of many electronic devices to bags that keep potato chips fresh for many months. Plasmas are even used for healing wounds.  All these applications involve interactions of plasmas with surfaces. Figuring out what happens on a surface exposed to plasma is an intellectually challenging problem, not only because plasma-surface interactions are complex but also our tool kit for studying these interactions is very limited. The standard tools of surface science work only in ultra high vacuum (UHV) and cannot be used in the plasma environment. A major addition was made to the arsenal of plasma and surface scientists a few years ago when Vincent Donnelly and coworkers at the University of Houston invented “the spinning-wall method.” In this method, the surface of interest is shuttled between a plasma chamber and a UHV analysis chamber using high-speed rotation.   In the Jan/Feb issue of JVST A, Donnelly and coworkers review the tools for studying plasma-surface interactions and describe the progress in understanding plasma-surface interaction in various material systems relevant to plasma processing: V. M. Donnelly, J. Guha and L. Stafford, “Critical review: Plasma-surface reactions and the spinning wall method,” J. Vac. Sci. Technol. A 29, 010801 (2011).

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Interfacial organic layers: Tailored surface chemistry for nucleation and growth

Kevin J. Hughes and James R. Engstrom

J. Vac. Sci. Technol. A 28, 1033 (2010);
doi:10.1116/1.3480920

The use of interfacial organic layers to promote nucleation and growth of inorganic thin films is reviewed.  The focus is on the fundamental aspects of inorganic-organic interface formation using transition metal coordination complexes and atomic layer deposition.  Three factors are identified as important in terms of promoting both chemisorption and subsequent smooth thin film growth and these are the identity, density, and dimensionality or spatial distribution of the functional groups in the organic layer.  Correlations are sought between phenomena occurring in the monolayer regime and that occurring in both the nucleation and the steady-state stages of thin film growth.  

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Interface-mediated ultrafast carrier conduction in oxide thin films and superlattices for energy

Shriram Ramanathan

 J. Vac. Sci. Technol. A  27, 1126 (2009); doi:10.1116/1.3186616

The role of interfaces in influencing high temperature carrier transport is a fascinating problem in solid state ionics. Understanding how internal interfaces or surfaces influence kinetics and thermodynamics of charge and mass transport can lead to design and discovery of novel energy materials. Chemical stability studies and electrolytic domain boundary identification in interface-controlled oxides can provide insights into the nature of carriers that are responsive under electrochemical potentials. The ability to design and synthesize ultra-fast ion conductors that are thermally and chemically stable in a range of temperatures and oxygen pressures could potentially impact electrochemical energy conversion and storage technologies including but not limited to solid oxide fuel cells.

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Mechanics of stretchable inorganic electronic materials

J. Song, H. Jiang, Y. Huang, J. A. Rogers

J. Vac. Sci. Technol. A  27, 1107 (2009); doi:10.1116/1.3168555

Brittle inorganic electronic materials can be deposited onto compliant substrates to develop stretchable electronics through the nonlinear buckling process. This paper reviews the mechanics of these materials, which reveals the fundamental physics and provides practical strategies for the construction of stretchable electronics.

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