Novel 3D solar cells to undergo testing in space

A novel 3D solar cell that was launched to the International Space Station (ISS) will be installed on the exterior of the station to study the cells' performance and their ability to withstand the rigours of space, scientists said.
An experimental module containing 18 test cells, developed by researchers at Georgia Institute of Technology (Georgia Tech), was launched to the ISS yesterday aboard SpaceX's Falcon 9 rocket from Cape Canaveral Air Force Station in Florida.
In addition to testing the 3D format, the module will also study a low-cost copper-zinc-tin-sulfide (CZTS) solar cell formulation.
"We want to see both the light-trapping performance of our 3D solar cells and how they are going to respond to the harshness of space," said Jud Ready, a principal research engineer at the Georgia Tech Research Institute (GTRI).

"We will also measure performance against temperature, because temperature has an influence on the performance of a solar cell," said Ready.
Built by coating miniature carbon nanotube "towers" with a photo-absorber that captures sunlight from all angles, the 3D cells could boost the amount of power obtained from the small surface areas many spacecraft have.

The cells would absorb light from any direction, eliminating the need for the devices to aim photovoltaics (PV) modules toward the Sun.
The PV cell experiment will be installed on the NanoRacks External Platform (NREP), where robustness of the solar cells will be studied under harsh space conditions for six months.

"The CZTS photovoltaic arrays were built using the readily available elements copper, zinc, tin and sulphur to replace rarer CIGS - copper, indium, gallium and selenium - which are used in similar thin-film solar cells," said Ready.
"The CZTS approach produces an efficient photo-absorber using earth-abundant materials that cost around a thousand times less than rare-earth elements like indium, gallium and selenium," he said.
The 3D capability could prove especially valuable on the ISS, which is exposed daily to 15-16 sunrises and sunsets as it orbits Earth every 92 minutes at 27,600 km per hour.
The 3D towers can exploit the Sun's rays for longer periods than conventional 2D planar - or flat - designs, which work most efficiently only when the sun is directly overhead.

"With our 3D design, as the Sun's angle increases more surface is exposed and there's a growing chance that photons will enter," Ready said.
"Also, 3D technology provides more opportunity for photons to bounce around between the towers, increasing the likelihood they will be converted to electron hole pairs and produce mobile charge carriers," he said.
As the ISS orbits, the 3D arrays' performance will be compared to a high quality commercial 2D planar cell array installed nearby.
If things go as expected, GTRI's cells will provide relatively better performance than the other cells as they move away from high noon.