August, 2015 | Sun Is The Future

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8 August

Dr. Christopher Case (of Oxford PV) Discusses Game-Changing Future Transformer of Solar Power Generation-Perovskite Based Solar Cell Technology

Dear Friends, Visitors/Viewers/Readers,

(Please click on red links & note magenta)

I saved the most potential game-changing solar technology in the last interview spot, the update of Perovskite-based solar cell technology with the Chief Technology Officer of Oxford PV, Dr. Christopher Case, of this series of Intersolar North America 2015 interviews. Recalling one of our earlier posts, I wrote about Perovskite, a calcium titanium oxide mineral discovered in the Ural Mountains of Russia in 1839. This new old material is generating quite an explosive buzz because scientists have found, in recent years, that it is a great material to be used in solar absorption applications. It can be made simply and inexpensively by using common wet chemistry lab methods and low cost equipments instead of the expensive deposition equipments common in the semiconductor industry. To take a look at how this process is made cheap and accessible, I’m sharing the video below:

These solar (photovoltaic) cells are made in tandem (layer by layer) fashion on a specially coated glass support. In the video above:

the glass is coated with a dense layer of titanium dioxide, by robotic arm, to prevent electrical charge generated by sunlight from leaking out of the cell.
a less dense porous oxide layer covers the dense oxide layer (usually titanium dioxide, other oxides may also be used).
a simple high speed spin coater deposits this layer from solution and spreads this coating evenly across the device.
heating this glass/device in an oven conditions it for solar cell use.
prepare the Perovskite material (which absorbs in the broad range of solar spectrum) by combining 2 precursor materials: PbI2 (lead iodide) & CH6IN (methylammonium iodide)
drip the liquid phase mixture (from 5.) onto the oxide coated device (from 4.)
spin the resulting device in 6 to assure even coating
applying halide solution
heating the device resulting from 8 on a hot plate–>spontaneously crystallizes precursors in freshly deposited liquid
color changes also result from crystallization process resulting from 9.

Such tandem product has the advantage of being able to be introduced into existing infrastructure of current silicon module manufacturing process, boosting its efficiency. With added few steps toward the end of the production line, the coating (equivalent to second solar cell) takes advantage of the blue portion of the solar spectrum and may improve the solar cell efficiency by 20-25% above the underlying silicon. The fact that Perovskite-based solar cell technology is of earth abundant material also insures its availability and low cost. Its high absorption in solar spectrum enables it to have comparable characteristics to that of gallium arsenide. Its ability to change its sensitivity to different band gaps in solar spectrum allows it to make different architectures in tandem solar cells. It can truly be considered as the Custom Solar Absorber! In short term, Perovskite-based solar cell may boost the efficiency level of existing technology and in the long term, it may be a stand-alone technology with closer efficiency level to that of gallium arsenide but at a much lower cost. It may potentially be sprayed, ink-jet printed, dip-coated, etc. It is no wonder that Dr. Case commented, “the perovskite in solar application is the fastest increasing photovoltaic efficiency of any solar photovoltaic thin film material ever! In just a few years, it went from a lab efficiency of about 6% to well over 17%…the material is a very good solar absorber….bringing the material to 25% efficiency in a monolithic layer and 30%+ in a perovskite tandem layer….potentially the future replacement for silicon.”

The perovskite thin-film solar cells, is currently being developed by Oxford PV (a spin-out from the University of Oxford in 2009-2010 to commercialize this technology, which has exclusively licensed the intellectual property developed by Professor Henry Snaith and his team of 20 scientists). Below, Professor Henry Snaith will embellish upon the development of this solar technology:

Oxford PV plans on continuing to optimize this technology’s cell efficiency and accelerate the transfer of the technology into production. Furthermore, it aims to develop the range of substrates to which the cells can be applied. With its promising future, we, the solar enthusiasts and investors alike, should keep our eyes on Oxford PV in the coming years. In the next few years, we anticipate that Dr. Henry Snaith and his team of scientists will continue to tackle challenges in trap densities, doping densities, mobility, mechanisms for free carrier generations, etc., to further improve device performance. You will find that many in the solar industry share the optimism of Professor Henry Snaith and Dr. Christopher Case.

For those of you interested in more details about Perovskite-based solar cell technology, please refer to the two videos below:

1. Introducing Perovskite Solar Cells to Undergraduates: