Full Spectrum Quantum Dot PV: Indium Nitride

Indium nitride is being studied to determine whether it can be made into a high efficiency photovoltaic material yielding a near full spectrum response under very harsh environmental conditions. NASA has awarded a contract to Magnolia Optical Technologies for this purpose.

"The goal of this STTR program is to develop high-efficiency solar cells that are resistant to extreme conditions while achieving high solar electric power conversion efficiency," said Dr. Roger Welser, Kopin's Director of Technology and New Product Development.

"The advanced solar cell structure incorporating InN-based nanostructures can harness a very large fraction of the solar spectrum while minimizing the effects of high temperatures and high-energy radiation. This technology will enable photovoltaic power systems of future NASA space exploration missions." __EnergyDaily

A full spectrum PV cell incorporating Indium would likely also include gallium, in a double layered, multi-spectrum cell.

The maximum efficiency a solar cell made from a single material can achieve in converting light to electrical power is about 30 percent; the best efficiency actually achieved is about 25 percent. To do better, researchers and manufacturers stack different band gap materials in multijunction cells.

Dozens of different layers could be stacked to catch photons at all energies, reaching efficiencies better than 70 percent, but too many problems intervene. When crystal lattices differ too much, for example, strain damages the crystals. The most efficient multijunction solar cell yet made -- 30 percent, out of a possible 50 percent efficiency -- has just two layers.

Indium gallium nitride's advantages are many. It has tremendous heat capacity and, like other group III nitrides, is extremely resist to radiation. These properties are ideal for the solar arrays that power communications satellites and other spacecraft. But what about cost?

"If it works, the cost should be on the same order of magnitude as traffic lights," Walukiewicz says. "Maybe less." Solar cells so efficient and so relatively cheap could revolutionize the use of solar power not just in space but on Earth. __Source

The race is on to capture the most solar spectrum at the highest electrical efficiency and lowest cost. Durability under extreme conditions is a must. Given the move to concentrating PV, resistance to heating and cooling stresses are extremely important.