Power/Performance Bits: July 23

Thinnest light absorber
Expected to potentially reduce the cost and improve the efficiency of solar cells, Stanford University scientists report they have created the thinnest, most efficient absorber of visible light on record. The nanoscale structure is thousands of times thinner than an ordinary sheet of paper.

The researchers said achieving complete absorption of visible light with a minimal amount of material is highly desirable for many applications, including solar energy conversion to fuel and electricity. The results show that it is possible for an extremely thin layer of material to absorb almost 100% of incident light of a specific wavelength. Thinner solar cells require less material and therefore cost less. The challenge for researchers is to reduce the thickness of the cell without compromising its ability to absorb and convert sunlight into clean energy.

For the study, the Stanford team created thin wafers dotted with trillions of round particles of gold. Each gold nanodot was about 14nm tall and 17nm wide.

These four wafers contain the thinnest light-absorber ever built. The absorber layer consists of billions of gold nanodots. Each round dot has a volume equivalent to a flat particle of gold 1.6-nanometers thick. (Source: Stanford University)

An ideal solar cell would be able to absorb the entire visible light spectrum, from violet light waves 400nm long to red waves 700nm in length as well as invisible ultraviolet and infrared light. In the experiment, the researchers were able to tune the gold nanodots to absorb one light from one spot on the spectrum: reddish-orange light waves about 600nm long.

Much like a guitar string, which has a resonance frequency that changes when you tune it, metal particles have a resonance frequency that can be fine-tuned to absorb a particular wavelength of light. The researchers tuned the optical properties of the system to maximize the light absorption.

The next step for the Stanford team is to demonstrate that the technology can be used in actual solar cells.

E-skin responds to touch
A research team at UC Berkeley has created the first user-interactive sensor network on flexible plastic. The new electronic skin, or e-skin, responds to touch by instantly lighting up. The more intense the pressure, the brighter the light it emits.

With the interactive e-skin, the researchers said they have demonstrated an elegant system on plastic that can be wrapped around different objects to enable a new form of human-machine interfacing.

Shown is a 16-by-16 pixel interactive e-skin created by UC Berkeley engineers. Organic LEDs light up when touched. (Source: UC Berkeley)

In addition to giving robots a finer sense of touch, the engineers believe the new e-skin technology could also be used to create things like wallpapers that double as touchscreen displays and dashboard laminates that allow drivers to adjust electronic controls with the wave of a hand.

The experimental samples of the latest e-skin measure 16-by-16 pixels. Within each pixel sits a transistor, an organic LED and a pressure sensor.

Integrating sensors into a network is not new, but converting the data obtained into something interactive is the breakthrough and unlike the stiff touchscreens on iPhones, computer monitors and ATMs, the e-skin is flexible and can be easily laminated on any surface.

~Ann Steffora Mutschler