‘Quantum dots’ technology to make solar cells more efficient, cheaper

Monday, February 21, 2011

WASHINGTON - Stanford researchers have developed a new technology that would increase the efficiency of solar cells three-fold and could lead to cheaper, more efficient solar panels.

The researchers stated that by adding a single layer of organic molecules such efficiency could be attained.

These solar cells used tiny particles of semiconductors called ‘quantum dots.’ Quantum dot solar cells are cheaper to produce than traditional ones, as they can be made using simple chemical reactions.

Solar cells work by using energy from the sun to excite electrons. The excited electrons jump from a lower energy level to a higher one, leaving behind a ‘hole’ where the electron used to be. Solar cells use a semiconductor to pull an electron in one direction, and another material to pull the hole in the other direction. This flow of electron and hole in different directions leads to an electric current.

But it takes a certain minimum energy to fully separate the electron and the hole. However, quantum dot solar cells do not share this limitation and can in theory be far more efficient.

For the new study, the researchers coated a titanium dioxide semiconductor in their quantum dot solar cell with a very thin single layer of organic molecules. These molecules were self-assembling, meaning that their interactions caused them to pack together in an ordered way.

The quantum dots were present at the interface of this organic layer and the semiconductor. The researchers tried several different organic molecules in an attempt to learn which ones would most increase the efficiency of the solar cells.

But she found that the exact molecule didn’t matter - just having a single organic layer less than a nanometer thick was enough to triple the efficiency of the solar cells.

But she said the result made sense in hindsight, and the researchers came up with a new model - it’s the length of the molecule, and not its exact nature, that matters. Molecules that are too long don’t allow the quantum dots to interact well with the semiconductor.

Bent’s theory is that once the sun’s energy creates an electron and a hole, the thin organic layer helps keep them apart, preventing them from recombining and being wasted. The group has yet to optimize the solar cells, and they have currently achieved an efficiency of, at most, 0.4 percent.

But the group can tune several aspects of the cell, and once they do, the three-fold increase caused by the organic layer would be even more significant.

The findings have been published in the journal ACS Nano. (ANI)

Filed under: Science and Technology

will not be displayed