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Broad-Spectrum Photosensor

Polymer plus fullerene yields photodetector that covers ultraviolet to near infrared

by Elizabeth K. Wilson
August 17, 2009 | A version of this story appeared in Volume 87, Issue 33

Credit: Courtesy of Alan Heeger
A mixture of the organic polymer PDDTT and the fullerene derivative shown yields a photodetector with a broad response.
Credit: Courtesy of Alan Heeger
A mixture of the organic polymer PDDTT and the fullerene derivative shown yields a photodetector with a broad response.

A promising new polymer photodetector material shows an unprecedented ability to detect photons throughout the full range of UV-Vis to near-IR wavelengths. Photosensors are ubiquitous tools in today’s technologies, used for remote sensing, surveillance, and environmental monitoring.

The new material, fabricated by a group that includes University of California, Santa Barbara, physics professor Alan J. Heeger, Cbrite Inc. senior scientist Xiong Gong, and their colleagues there and at South China University of Technology (SCUT), in Guangzhou, could be used to make a single device that would replace the three devices—typically based on GaN, Si, and InGaAs—currently required to cover this spectral range.

Scientists have been exploring the combination of polymers and fullerenes as photodetectors since the early 1990s. Heeger won the Nobel Prize in Chemistry in 2000 for his work on conductive polymers.

The advantages of polymer photodetectors are many. For example, whereas today’s inorganic IR silicon-based photodetectors require cooling to about 4 K, polymer photodetectors can operate at room temperature. The thin, light polymer materials can also be fabricated into different shapes.

Numerous researchers have developed detectors with sensitivities at wavelengths ranging from 400 to 900 nm, but this new material is the first to detect the full UV-Vis to near-IR spectrum, ranging from 300 to 1,450 nm.

“The work is very exciting,” says Yang Yang, a UCLA materials science professor whose group focuses on organic electronic materials and devices. The paper will “open a new direction for polymer electronics,” he adds.

Yang also notes that this particular polymer—known as PDDTT and developed by SCUT chemistry professor Yong Cao—has an unusually small bandgap. “Often when a bandgap becomes this small, it could become a conductor,” he says.

The group spin-cast the polymer with a fullerene derivative into thin films. It is now fabricating arrays of the detectors, as well as examining ways to expand the spectral response of this class of photodetectors, Gong says.



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