FEATURE SOLAR
The race for renewables
New solar harnessing materials along with novel production techniques are improving the efficiency of solar power. Rachel Berkowitz looks at the latest advances in photovoltaics
T
he 2015 United Nations Conference on Climate Change (COP21) held in Paris last December initiated noteworthy steps toward a clean energy future. Among these was the launch of the Global Solar Council. The principal members of the organisation, whose aim is to unify the solar power sector at an international level, are solar associations from established and emerging markets. As noted by SolarCity founder Elon Musk at the 2015 American Geophysical Union meeting, ‘you could take basically a corner of Utah and Nevada and power the whole United States with solar power’. But while the international community acknowledges the value of solar power and the
16 ELECTRO OPTICS l MARCH 2016
sun offers sufficient energy, the photovoltaics industry has a way to go before it can sustain our society’s demand for energy. Part of the challenge lies in storage technology; but equally important is the efficiency of solar cells themselves. Silicon dominates the solar market, but modern panels can only harness a single wavelength of light. This means that only a fraction of the sun’s available energy is actually captured. Developing materials that can not only harness multiple wavelengths but also do so efficiently and affordably is critical for the photovoltaics industry. Along with specialised materials comes the need for specialised devices to characterise their properties and bring the industry to the same level as other key energy sources.
Silicon records There are two ways of structuring silicon solar cells. Both-sides-contacted devices have metal current-carrying contacts on front and back, while back-contacted devices have contacts only on the rear. The record efficiency for back-contacted cells is 25.6 per cent, and in principle can be higher than both-sides-contacted cells. However, back- contacted devices require extensive structuring processes, making production costly.
‘The market share of both-sides-contacted cells is over 99 per cent and there are a lot of improvements in... technologies that help to boost [their] efficiency,’ explained Martin Hermle, head of the high efficiency solar cells department at Germany’s Fraunhofer Institute for Solar Energy Systems (ISE).
Last autumn, Fraunhofer ISE set a new
efficiency record of 25.1 per cent for both- sides-contacted silicon solar cells. Hermle led the development of the record-setting Tunnel Oxide Passivated Contact ‘TOPCon’ technology, which features a novel full-area passivated back contact. The selective passivated contact enables electrons to tunnel through, while preventing recombination. A silicon coating completes the combination of layers that allows electrical current to flow from the cell with nearly zero loss. Most solar cells have an aluminium-alloy contact covering the entire back surface. But the contact’s high recombination and low internal reflection limits efficiency. Therefore, the industry retrofits production to incorporate Passivated Emitter Rear Cell (PERC) technology. PERC increases efficiency by adding a dielectric passivation layer in small areas, to reduce surface recombination. However, it requires additional
@electrooptics |
www.electrooptics.com
Sandro/
Shutterstock.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44