Researchers Discover New Way to Split and Sum Photons with Silicon – UT News

A team of researchers at The University of Texas at Austin and the University of California, Riverside have found a way to produce a long-hypothesized phenomenonthe transfer of energy between silicon andorganic, carbon-based moleculesin a breakthrough that has implications for information storage in quantum computing, solar energy conversion and medical imaging. The research is described in a paper out today in the journalNature Chemistry.

Silicon is one of the planets most abundant materials and a critical component in everything from the semiconductors that power our computers to the cells used in nearly all solar energy panels.For all of its abilities, however, siliconhas some problems when it comes to converting light into electricity.Different colors of light are comprised of photons,particles that carry lights energy. Silicon can efficiently convert red photons into electricity, but withblue photons, whichcarry twice the energy of red photons, siliconloses most oftheenergy as heat.

The new discoveryprovides scientists with a way to boost silicons efficiency by pairing it with a carbon-based material that converts blue photons intopairs of red photons that can be more efficiently used by silicon.This hybrid material can also be tweaked to operate in reverse, taking in red lightand converting it into blue light, which has implications formedical treatmentsand quantum computing.

The organic molecule weve paired silicon with is a type of carbon ash calledanthracene. Its basically soot, saidSean Roberts, a UT Austin assistant professor of chemistry. The paper describesamethod for chemically connecting silicon to anthracene, creating a molecular power line thatallowsenergy to transfer between the silicon and ash-like substance. We now can finely tune this material to react to different wavelengths of light. Imagine, for quantum computing, being able to tweak and optimize a material to turn one blue photon into two red photons or two red photons into one blue. Its perfect for information storage.

For four decades, scientists have hypothesized that pairing silicon with a type of organic material that better absorbs blue and green light efficiently could be the key to improving siliconsability to convert light into electricity. But simply layering the two materials never brought about the anticipatedspintriplet exciton transfer,a particular type of energy transfer fromthe carbon-based material to silicon,needed to realize this goal. Roberts and materials scientists at UC Riverside describe howthey broke through the impasse with tiny chemical wires that connect silicon nanocrystals toanthracene, producing the predicted energy transfer between them for the first-time.

The challenge has been getting pairs of excited electrons out of these organic materials and into silicon. It cant be done just by depositing one on top of the other, Roberts said. It takesbuilding a new type of chemical interface between the silicon and this material to allow them to electronically communicate.

Roberts and his graduate student EmilyRaulersonmeasured the effect in a specially designed molecule that attaches to a silicon nanocrystal, the innovation of collaborators Ming Lee Tang, LorenzoMangoliniand Pan Xia of UC Riverside. Using an ultrafast laser, Roberts andRaulersonfound that the new molecular wire between the two materials was not only fast, resilient and efficient, itcould effectivelytransfer about 90% of the energy from the nanocrystal to the molecule.

We canuse this chemistrytocreate materials thatabsorb and emit anycolorof light, saidRaulerson, who says that, with further fine tuning, similar silicon nanocrystals tethered to a molecule could generate a variety of applications, from battery-less night-vision goggles to new miniature electronics.

Other highly efficient processes of this sort, called photon up-conversion, previously relied on toxic materials. As the new approach uses exclusively nontoxic materials, it opens the door for applications in human medicine, bioimaging and environmentally sustainable technologies, something thatRoberts and fellow UT Austin chemist Michael Rose are working towards.

At UC Riverside, Tangs lab pioneered how to attach the organic molecules to the silicon nanoparticles, andMangolinisgroup engineered the silicon nanocrystals.

The novelty is really how to get the two parts of this structurethe organic molecules and the quantum confined silicon nanocrystalsto work together, saidMangolini, an associate professor of mechanical engineering. We are the first group to really put the two together.

The papers other authors include Devin Colemanand CarterGerkeof UC Riverside.

Funding for the research was provided by the National Science Foundation, the Robert A. Welch Foundation, the Research Corporation for Science Advancement, the Air Force Office of Scientific Research and the Department of Energy. Additionally,Raulersonholds the Leon O. Morgan Graduate Fellowship at UT Austin.