Measurement Advance Could Speed Solar Innovation

A new automated measurement system that accurately and quickly measures the electric power output of solar energy devices could soon help researchers and manufacturers to develop next-generation solar energy cells.

Innovative devices that convert sunlight to electric power more efficiently and cost-effectively than the current generation of solar cell technology are the objects of a global pursuit, according to NIST (National Institute of Standards and Technology) researchers, especially in the race to secure pole position in the competition for fast-growing international markets for clean energy resources.

The NIST researchers combined 32 LEDs — each generating light from different segments of the solar spectrum — and other off-the-shelf equipment with their own custom-made technologies to build a system that measures the wavelength-dependent quantum efficiency of solar devices over a relatively large area.

Sections of the new NIST measurement system's LED plate are shown. A water-coolant system on the back (a) keeps the operating temperature constant. Collectively, the different-colored LEDs (b) generate light in wavelengths covering much of the solar spectrum. LEDs in the second row from the bottom emit most of their radiation in the near-infrared region and appear very faint to the human eye. Light from the last row of LEDs is completely invisible. (Image: NIST)

In comparison with current approaches, the new system could offer significant advantages, such as greater speed and ease of operation, more uniform illumination and a service life that is about 10 times longer.

The system for measuring spectral response easily accommodates two unique but complementary methods for determining how much electric current a solar device generates when hit by a standard amount of sunlight. Both methods are straightforward, and they use the same hardware setup. With either method, the automated system produces measurements more rapidly than current instruments used to simulate solar radiation and to characterize how efficiently a device converts light energy to electric energy.

One method, which activates the LED lights sequentially, is less subject to interference than the other technique, yielding a spectral response measurement in about 6 min. The other method activates all 32 LEDs simultaneously, but each LED generates pulses of light at a different rate. The solar response of a photovoltaic device over the entire LED-blended spectrum can be determined in about 4 s.

Although the faster method is more susceptible to interference, it has the potential for in-line manufacturing tests for ensuring quality, the NIST scientists said.

Next, the team plans to push its technology further to achieve certain goals, such as matching or exceeding the energy intensity of the sun, broadening the LED-synthesized spectrum to include the infrared portion of the sun’s output, and consistently achieving measurement results with uncertainties of less than 1 percent.

Their current work, however, has demonstrated that LEDs are now “technologically viable” for use in solar simulators and for characterizing photovoltaics and other photoelectric devices, said NIST physicist Behrang Hamadani.

The findings were reported in Applied Optics.

For more information, visit: www.nist.gov