Transcriber: Denise RQ Reviewer: Ariana Bleau Lugo
It's sunny somehwere in the world just not in Toronto today.
But the average person watching this online
is sitting somewhere
where the sun is beaming down on them.
It's an incredibly abundant and clean resource.
Another way to look at its abundance it's to say
that if we were to cover a quarter of the area of the state of Nevada
with resonably efficient solar cells, the kind that we can make today,
then that would be sufficient
to power the Earth's energy needs for overall time in a steady state.
So the sun is clean, it's abundant, and most importantly it's free.
So, why on earth are we relying on
these legacy fossil fuels to the extent that we are?
Well, the answer actually does come down to cost.
Not the cost to the sun's free energy.
It comes down to the cost of the harvesting technologies
that we have at our disposal today.
Let me illustrate how important the cost of the technologies is.
If we don't do anything different from what we're doing now,
we just extrapolate the rate of which solar cell technologies
are getting a little bit cheaper every year, just incrementally cheaper,
then, on the left is the case for 2030, for the year 2030.
By that time, it will make purely rational economic sense
to put solar pannels at a kind of modest level.
We would've revolutionized or transformed
the way in which we harness energy.
And that's 20 years up.
On the right is the case, if we have a breakthrough
in the cost of harvesting solar energy.
It's all about the technology, it's not about a basic physical limit.
It's not that we can't do this, it's that we'd have to work hard
and invest and work in teams in order to solve this practical problem.
So that's what my group at the University of Toronto does.
We're trying to re-think, re-design, re-imagine the solar cell.
Today, the solar cell is made out often of silicon, a beautiful semiconductor material.
It's the semiconductor material
that's revolutionized information technology.
It transformed our lives.
But it's an approach that relies on perfection, on purity,
on heating the silicon to 1,000 degree Celsius,
on making a perfect crystal,
a crystal that's kind of thick, a crystal that's rigid.
And you can translate that rigidity and that thickness and that cost
and that thermal budget into a financial cost.
Not just the cost of the cell, but the cost of installing the cell as well.
And so our view is that we could transform, we could revolutionize this field
if we could print solar cells the way we print newspapers,
if we can make a semiconductor ink
that we could print onto a flexible backing like the one showing here.
And then, not only would we've made a very manufacturable approach
making solar cells feel like printing newspapers,
we would also have the ability to deploy them so much more easily.
We have these light weight carpets that we'd roll out on a rooftop.
So it's a really exciting challenge, it's a really important possibility.
Here's a picture of some of
the semiconductor inks that we make.
This is on the small scale.
We're just dropping a droplet of this dark stuff.
It absorbs all of the light
and we actually just rotate this little transparent substrate,
the droplet of ink spreads out,
covers the substrate very uniformly, which it needs to do.
Here's one of the finished cells.
This is just a square inch kind of illustration.
So it's a small prototype, a bunch of different electrical contexts.
That's part of the game here, as well as absorbing the sun's energy.
As well as turning it into electrons that can flow in the form of current,
we need to extract that current and we need to put these electrons
on one side that are opaque, and transparent on the other side.
Now the inks that we work with are called quantum dots or nano crystals.
Here's a real super close-up picture of them.
This is actually taken using a transmission electron microscope.
So these are configured on a scale of few nanometers,
a few billionths of a meter, incredibly small,
and their smallness, combined with
these little molecule-based wrappers that we wrap around them
allow us to make what's called a colloid, which is like paint.
In a solvent, you can disperse the solid material, if it's small enough,
and it it's wrapped up in something, that will cause it to want to stay in solution.
So that paint that you saw on the previous page
it worked, it was a dispersion
because of the way we engineered the surface
at the scale of the nanometer, the scale of molecules and atoms.
Now there's another aspect to the way these solar cells work
that's got me really excited and that's the fact that,
as well as making them sprayable or paintable,
we also make them tunable.
So, you know, the sun, obviously, is a rainbow of colours
as we can see when the rainbows come out --
hopefully one will today --
and we mirror that rainbow in our materials.
We make a mirror of colors, a rainbow of colors
across the visible spectrum but also in the infrared.
We were able to engineer our materials such that
they're very strong absorbers of the half of the sun's power
that resides in the infrared wavelengths as well as in the visible.
And just recently we've figured out how to shrink the wrappers --
that wrap the semiconductor particles up and protect them --
smaller and smaller, so they are now just an atom thick.
And so these particles can be rendered
really closely packed together, really tightly knit.
We've kind of made a nano cement
in which these particles are made into a solid material once they dry.
It's very, very dense and very, very well protected.
So what is this all leading to?
What could it mean?
If we can make, if we can fully realize
the potential of this amazing resource, which is so vast, so abundant
and with the resource itself, the fuel --
you know, the sun's power is free to us --
if we can harvest it in this cost effective way,
what could it mean, where could it go?
Well, of course we'll start
with the roofs of homes and the roofs of factories
in Mississauga and in Shenzhen and around the world.
But why, why stop there?
Once we have this flexible light capturing material
why not on our backpacks or on our tablet PCs?
Why not the cell of a sail boat?
Why not integrated into the materials that make up your electric vehicle?
Why not conform these light harvesting, energy harvesting materials into your EV?
And that's just in this geography. Let's think globally.
What about making one of these materials so cost effective
that we can use it during the day
to charge the battery of a home, perhaps somewhere in Sub-Saharian Africa.
And then, in the evening, use that energy,
play it back to power a light bulb
so that somebody can read or study in the evening
or to power a laptop.
The implications of the democratization of energy
through low cost solar technologies are tremendous,
they're global and they're human.
Thank you!
(Applause)