One of the tours offered to community members this month at Los Alamos National Laboratory took them behind the security fence to the Center for Advanced Photophysics. There, bent over spectroscopes, reaching into glove boxes and turning on high-powered lasers in darkened rooms, free of dust and ambient vibrations, a team of about 30 people are working to realize a more perfect solar cell.
At the time, the project was up for renewal, along with 46 other national Energy Frontier Research Centers funded by the Department of Energy. Not much was said about that, but the question hung in the air. The LANL project had built a team, published papers, increased efficiencies and found a way forward. But was that enough in an era ruled by policy uncertainties and shrinking budgets in Washington, D.C.?
LANL is a national security science laboratory that specializes in “all things nuclear,” as LANL Director Charles McMillan described it earlier that day. In that environment, solar cell research is one of the few projects outside the circle of nuclear weapons, nuclear energy, nuclear threat reduction, nonproliferation and nuclear waste management and related scientific activities that make up about 90 percent of lab operations.
The Center for Advanced Photophysics is in its fifth year working on what are known as third generation solar cells. The first solar cells were expensive and inefficient; second generation cells were even less efficient, but quite a bit cheaper. The goal for the third generation is to maximize efficiency and minimize cost.
“The question is how to harness solar light efficiently,” said Victor Klimov, the project director. “The focus was photovoltaic devices. We’re still going to have those, but now with some new elements and new directions.”
In April, the laboratory announced development of a house window in collaboration with scientists from the University of Milano-Bicocca, Italy, that serves as a solar panel. Called a luminescent solar concentrator, the fabricated device makes use of quantum dots, specialized bits of semiconductor material developed by researchers at the Los Alamos to harvest photons from the sun and channel them into a solar cell.
Quantum dots have been around since the early 1980s, but science did not come up with a role for them until 2002. According to the journal Nature, that was when cell biologists began to use them to give bio-molecules like proteins a fluorescent identifier.
“They are very small, 2 to 10 nanometers in diameter – about the size of 50 atoms,” said Istvan Robel, a staff scientist, introducing the tour. “In about the time it takes you to say ‘one Mississippi,’ your fingernail grows about one nanometer.”
The small size and relative simplicity of the components means that nano-engineered dots can be made in mass quantities at a fraction of the cost of current devices.
“The goal is solar paint,” said Robel. “You put it on the roof and there you go.”
The project is of particular interest to New Mexico, he pointed out, because the state happens to be one of the “richest solar patches” in the country. “Seven percent of New Mexico (land area) could power the U.S.,” he said.
Quantum dots are artificial atoms that can be fine tuned to express subtle mixtures of solid state and quantum properties. By exploiting qualities of quantum containment, selective absorption and deflection, they can make solar energy production more efficient. A LANL announcement this week claimed almost four times the yield of what is called “carrier multiplication,” the ability of a single photon to excite several electrons. By altering their dimensions, for example, quantum dots can be correlated with great precision to any given color, which gives them advantages in filtering and processing the full spectrum of light, including the blue and ultraviolent rays that are now wasted in producing heat rather than producing charge. In another dimension they can multiply the effect of each photon they take in, while minimizing energy wasted in heat.
On Wednesday, the Department of Energy announced the new round of awards. Out of the original 46 centers, only 22 – fewer than half — were renewed. But that did include the Center for Advanced Photophysics at Los Alamos, the only one of three Energy Frontier Research Center in New Mexico to be sustained. Ten new centers were started, but as expected the funding was reduced from five years to four and from an average of about $4 million a year to an average of $3 million a year, Klimov said.
“We survived very tough competition,” he added, obviously relieved and gratified, but at the same time faced with the next set of challenges.