ERC Researchers Demonstrate Silicon-Based Device as First Step toward Capturing Sun's Full Spectrum

Achievement date: 
2014
Outcome/accomplishment: 

Researchers affiliated with the NSF-funded Engineering Research Center (ERC) for Quantum Energy and Sustainable Solar Technologies (QESST), which is headquartered at Arizona State University, have demonstrated an all-silicon-based device that generates current in response to currently uncaptured portions of the sun’s spectrum.

Impact/benefits: 

Silicon is today's workhorse photovoltaic (PV) technology, but it can only absorb approximately one-third of the solar spectrum because much falls below what is called the bandgap energy. By demonstrating an all silicon-based device able to generate current in response to sub-bandgap light, the QESST researchers achieved a significant advance over traditional approaches and a major first step toward devices that can capture the full spectrum of the sun. 

Explanation/Background: 

Researchers in the past have attempted to capture and utilize this sub-bandgap light by introducing impurity states within the bandgap. Traditional methods of impurity incorporation, namely thermal annealing, result in relatively low amounts of impurities over very large sample volumes, thus limiting the potential benefit of this effect. Recently, researchers at MIT and four collaborating institutions used a technique known as pulsed-laser recrystallization to create a ~100 nm- thick film with up to ~1% gold impurity concentration, confining a very high impurity concentration to the near-surface region of a silicon wafer. The resulting single-crystalline material contained over three orders of magnitude higher gold concentration than the maximum equilibrium solid solubility—greatly exceeding the capabilities of thermal annealing. Photodiode devices fabricated from this gold-hyperdoped material exhibited photocurrent in response to 1,550 nm light under low-bias conditions (see figure).