TECHNOLOGY SPOTLIGHT

—by Stephanie Gooch

Chemists at UC Berkeley have developed plastic solar cells that may prove to be a cheaper, more versatile alternative to delicate silicon cells. By dispersing tiny nanorods 7nm in dia. by 60nm long in an organic semiconducting polymer, these researchers can capture specific wavelengths of light to generate electrical current. Instead of requiring clean-room facilities (as used in conventional polycrystalline silicone or crystalline gallium arsenide photovoltaics), cadmium selenide nanocrystals are grown in relatively dirty conditions in a beaker solution. The crystals are then mixed with P3HT plastic and coated onto a transparent electrode at 200nm thickness. An aluminum coating acts as a back electrode. The nanorods absorb light of a particular wavelength and generate an electron plus an electron hole. The electron travels the length of the nanorod and is collected by the aluminum electrode. The hole transfers to the hole-carrier plastic and thereby to the electrode, creating the current. At present, efficiency levels run around 1.7% (compared to 10% efficiency of conventional commercial solar cells, and 35% efficiency cap for top-of-the-line models). However, the research team is confident that by aligning the nanorods in a perpendicular fashion and packing them tightly, they can achieve target efficiencies. UC Berkeley or connect at www.rsleads.com/205df-152

In February we covered optical guitar pickups; now we turn to sound-induced light—sonoluminescence, produced by bombarding liquids with sound. During the negative pressure phase of the sound wave, pressure drops below vapor pressure and tiny bubbles can grow in volume by a factor of 1,000. During the subsequent positive phase, these bubbles collapse and the energy accumulated by the bubble growth is released. This acoustic cavitation can produce intra-bubble temperatures approaching 10,000°C. The internal gases can be heated to incan-descence and emit light. Increasing the energy within the collapsing bubbles (by increasing the volume of the growing bubbles) by a factor of one million can create the temperatures re-quired for nuclear reactions (tabletop-fusion?). Experiments conducted with chilled deuterated acetone used a pulsed neutron generator to shoot 14 million electron volt (MeV) neutrons into the liquid, with the intention of fusing two deuterium nuclei. The reaction had two statistically equal possibilities: either helium and a 2.5-MeV neutron would be produced, or tritium and protons would be released. Investigators sought the 2.5-MeV neutron and tritium as signatures for the reaction. Small amounts of tritium statistically above ambient levels were detected during this experiment, whereas tritium was not observed during cavitation of non-deuterated acetone. This “bubble fusion” is currently under confirmatory experimentation. Oak Ridge National Laboratory, or connect at www.rsleads.com/205df-153