Solar cell mystery solved, expected to greatly increase efficiency

spiro-OMeTAD
(Left) The set-up used to grow single crystals of spiro-OMeTAD, based on antisolvent vapor-assisted crystallization. (Right) Single crystal structure of spiro-OMeTAD. Credit: Shi, et al. ©2016 AAAS

(Phys.org)—For the past 17 years, spiro-OMeTAD, has been keeping a secret. Despite intense research efforts, its performance as the most commonly used hole-transporting material in perovskite and dye-sensitized solar cells has remained stagnant, creating a major bottleneck for improving solar cell efficiency. Thinking that the material has given all it has to offer, many researchers have begun investigating alternative materials to replace spiro-OMeTAD in future solar cells.

But in a new study published in Science Advances, Dong Shi et al. have taken a closer look at spiro-OMeTAD and found that it still has a great deal of untapped potential. For the first time, they have grown single crystals of the pure material, and in doing so, they have made the surprising discovery that spiro-OMeTAD's single-crystal structure has a hole mobility that is three orders of magnitude greater than that of its thin-film form (which is currently used in solar cells).

"This paper reports a major breakthrough for the fields of perovskite and solid-state by finally clarifying the potential performance of the material and showing that improving the crystallinity of the hole transport layer is the key strategy for further breakthroughs in device engineering of these solar cells," Osman Bakr, a professor of engineering at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia and leader of the study, told Phys.org.

The findings suggest that, at least in the short term, the time-consuming process of designing and synthesizing radically new organic hole conductors as replacements to spiro-OMeTAD may not be necessary.

In general, and dye-sensitized solar cells are made of three critical layers. Two of these layers—the electron-transporting layer and the light-absorbing layer—are well-understood structurally. However, the mesoscale packing structure of the hole-transporting layer, which is usually spiro-OMeTAD, has so far eluded researchers, and consequently its charge transport mechanisms have remained a mystery.

In the new study, the researchers figured out a way to grow pure single crystals of spiro-OMeTAD by dissolving the spiro-OMeTAD in a carefully chosen solvent. They then placed this vial inside a larger vial containing an antisolvent, in which spiro-OMeTAD does not dissolve as well, and allowed the antisolvent vapor to slowly diffuse into the inner vial. Eventually the solution in the inner vial becomes supersaturated, so that not all of the spiro-OMeTAD can stay dissolved, causing the spiro-OMeTAD to crystallize. The researchers then performed a variety of measurements on the crystals to investigate their charge transport mechanisms and other properties.

The results are much more encouraging than expected, in many ways running contrary to the conventional wisdom based on the material's large-scale structure, which suggested that the material had reached its limits.

Although the method used here to grow single crystals cannot be performed at a large scale, the researchers predict that similar methods that use an antisolvent to trigger crystallization could be used to enhance the crystallinity of the thin-layer spiro-OMeTAD, improving its hole mobility in order to make more efficient solar cells.

"These astonishing findings open a new direction for the development of perovskite solar cells and dye-sensitized by showing the still untapped potential of spiro-OMeTAD," Bakr said. "They unravel a key mystery that has confounded the photovoltaic community for the last 17 years."


Explore further

Pinholes be gone

More information: Dong Shi, et al. "Spiro-OMeTAD single crystals: Remarkably enhanced charge-carrier transport via mesoscale ordering." Science Advances. DOI: 10.1126/sciadv.1501491

Abstract
We report the crystal structure and hole-transport mechanism in spiro-OMeTAD [2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenyl-amine)9,9′-spirobifluorene], the dominant hole-transporting material in perovskite and solid-state dye-sensitized solar cells. Despite spiro-OMeTAD's paramount role in such devices, its crystal structure was unknown because of highly disordered solution-processed films; the hole-transport pathways remained ill-defined and the charge carrier mobilities were low, posing a major bottleneck for advancing cell efficiencies. We devised an antisolvent crystallization strategy to grow single crystals of spiro-OMeTAD, which allowed us to experimentally elucidate its molecular packing and transport properties. Electronic structure calculations enabled us to map spiro-OMeTAD's intermolecular charge-hopping pathways. Promisingly, single-crystal mobilities were found to exceed their thin-film counterparts by three orders of magnitude. Our findings underscore mesoscale ordering as a key strategy to achieving breakthroughs in hole-transport material engineering of solar cells.

Journal information: Science Advances

© 2016 Phys.org

Citation: Solar cell mystery solved, expected to greatly increase efficiency (2016, April 24) retrieved 21 September 2019 from https://phys.org/news/2016-04-solar-cell-mystery-greatly-efficiency.html
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Apr 24, 2016
When studying Mechanical Engineering in the late 90's, I learned that growing an entire jet engine turbine blade from a single, microscopic crystal led to an extremely high performance blade. It would be interesting to know what other problems have been solved by creating a macroscopic structure composed of only one crystal.

Apr 24, 2016
We need to stick with oil and releasing carbon to increase global warming so that progressives can use the global warming political issue to create a progressive world government that will replace inefficient free capitalist markets and democracy with bureaucratic dictatorship of the world economy. Methane is the revolution that gives power to the people while solar power is the chain capitalist fat cats use to enslave the proletariat.

Apr 25, 2016
It will be interesting to see how this plays out in the marketplace, when it gets there.

Apr 25, 2016
Interesting that this research is coming out of Saudi Arabia, apparently even they see the need to move their economy past oil.

Apr 25, 2016
Interesting that this research is coming out of Saudi Arabia, apparently even they see the need to move their economy past oil.

You might find this interesting.

http://www.theatl.../395315/

Apr 25, 2016
This comment has been removed by a moderator.

Apr 25, 2016
Grow dem crystalz in space, cuz in space dey' got noooo gravity fields to muck up da' process. Nice to have three orders of magnitude better collectors. Den' me 250 watt panel produces 250,000 watts....etc...etc. Nawwww, cuz' now if'n ya' believe dat'! Den I gots' sum b-a-a-a-d reeel esstate down in Florida, where dey' blow da' heads of'n minorities with high voltage electricity with "Ole Sparky".

Apr 25, 2016
Russia has announced the success of a perovskite flexible solar cell of high efficiency. Co-incidence huh?
This global warming--could it be because the US has long promoted gas engine cars which produce 20000 ppm of CABON MONOXIDE WHICH GRABS AN OXYGEN TO BECOME CARBON DIOXIDE. Might this explain the rise in autism, LD, and other classifications from the DSM?
The obvious solution is solar yet corps are not willing to bypass profit thru cars as compressed natural gas requires consumption as a new profit stream. Intelligence be damned.

Apr 25, 2016
We need to stick with oil and releasing carbon to increase global warming so that progressives can use the global warming political issue to create a progressive world government that will replace inefficient free capitalist markets and democracy with bureaucratic dictatorship of the world economy. Methane is the revolution that gives power to the people while solar power is the chain capitalist fat cats use to enslave the proletariat.


another antigoracle sockpuppet, (i r baboon style) he has a bout 27, now monkey, i know yo like your hollow tree stump to be full of carbon, but real people don't, living in lala land won't make you grow a few more braincells however.

Apr 25, 2016
Interesting that this research is coming out of Saudi Arabia, apparently even they see the need to move their economy past oil.

You might find this interesting.

No antisciengorilla sock, not interesting at all, they could cre less for the health of the planet:

"Now, Saudi rulers say, things must change. Their motivation isn't concern about global warming; the last thing they want is an end to the fossil-fuel era. Quite the contrary: they see investing in solar energy as a way to remain a global oil power."

Apr 25, 2016
Interesting that this research is coming out of Saudi Arabia, apparently even they see the need to move their economy past oil.


Furthermore interesting, they announced the other day that they are capitalizing 5% of ARAMCO (the national Saudi Arabia petrol company) and thereby creating the world's largest : 2 trillion USD. Now that's a real deal. We all know that a substantial amount of money (in absolute terms) can bring the change we need to happen, now hopefully they are indeed going to push the Earth towards Earth 2.0 (by 2020 they say).

Hopefully they end up selling the other 95% to cash-in 40 trillion (is this even possible actually?) and invest worldwide for a green economy.

http://www.bloomb...-off-oil

May 23, 2016
to the point, i read the most backward short sighted and narrow minded comment just now. for philstacy9 the flawed and dismal suggestion makes me truly weep for our species and our longevity, the reason that we are stuck fighting and scrapping just to live is exactly the ideas you want to perpetuate as if at some point everything will stop and people will all start making a better world...... after they push it beyond any hope of revitalization. thats the worst idea that i can remember in a long time, you need to think about the fact that if we started to work as a collective species and endeavor to make the necessary steps at this point then soon we will be far beyond the limits of most imaginations. use science to help not hinder us please.

May 23, 2016
just a brief addition, im a quantum theoretical scientist with additional quantum mechanics experience so im a realist, but for us to be a viable and growing species we are going to have to start out doing hard things that pay the top levels of the worlds rulers and governments. but the fruit we reap from a constant push against the oil companies , chemical pollutants, and the fat cats that back the money will lead the world into a era of combined efforts instead of clashing armies and by working together as many we stand a greater chance for a quicker and less painful transition into our next evolutionary state. i think thats a really ideal solution but its the correct one so maybe if more people looked at the broader picture and not just 1 lifetime then they too may change quickly.

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