Like it today to.

Be hosting the.

Birth I believe altering hope.

In material.

And we are live today that
we could be joined by

representatives from state
Walter to have a chance to he

writes Nelson is here as well
as a couple of our local.

People and today here our signal
all creatures lecturer is his name.

Is University of Oxford and
people may know of his work

recently in the area or off site so
it's still going to get it Ph D..

At Cambridge with their friends working on
their get a photo voltaic materials and

then he did a stint over
it he goal of my record.

In the area was so so that he returned
to Cambridge for a period of time

before settling it Oxford where he is now.

Every head is in the period of
two years I believe gotten both.

Going.

To the Royal Society.

In English which is he's a fellow
corrupt society which is a remarkable

accomplishment of itself and
you get tell us today about

some advances in prostate so cells and.

Leaflets all welcome here and
here we have to say.

Thank you thank you very much for
that I'm very nice introduction for

inviting me here it's my
first time to Georgia Tech so

it's been very enjoyable so far I hope
this collection isn't a disappointment for

you and you enjoy this to
have otherwise when people.

And invited again.

So I'm going to talk to you about her off
Skype kind of thing which way to look

a look at it maybe i'm before I do
that I'm just going to talk about P.V.

in general that is probably quite
a few of you in the audience who.

Are very much motivated towards P.V.
research so

I won't be don't spend too long on this
part but some of you might not be maybe

you'll be more motivated off to
the next few slides I don't know.

All these areas represent sort of resume
says you will know this to a certain

extent there's various amounts of coal
we could last for nine hundred terawatt

he has so probably about two
hundred years of electricity supply

all these other things and of course what
do them by quite a long way his solar and

that area represents the amount of
sunlight landing on the Earth every year

compared to the total resources of all
the other things so we've got plenty of

results I'm to try to put that in terms
of a sort of area of land required for

producing electricity from P.V.
this is a map of the world with the solar

radiance shown here where the sunniest
places have on average three hundred fifty

watts per square meter I think you're
probably pretty sunny summer down here

about two hundred maybe one hundred fifty
to two hundred watts per square meter

well less sunny in the U.K.
So we just got to live with that I suppose

not as bad as Scotland there's
always someone resident here.

But basically the point is we don't need
to cover very much area of the earth now

these but black dots from space they look
small but obviously that's quite a large

area but I'm going to put into perspective
compared to farming this is the Mount

of area that we need factually feeding
ourselves about half the planet and

over about half of the planet about
sixty percent of it's used for

producing life stocks are basically for
making producing meat and

milk we use a quarter of the planet so
compared to that this.

To produce or are saying the power of

even relatively inefficient cells we
need a fairy small fraction of that so

we're not going to displace any food by
producing electricity from satellite even

if we use prime farming land
which we don't need to.

This is not so relevant to you because
it's about the U.K. but you can maybe

multiply it by two half the areas required
just to put into real perspective how

much area do we need for P.V. compared
to other things we've got so in the U.K.

the amount of area used for buildings per
person is about forty eight square meters

it's about sixty three and again farmland
about two thousand square meters the U.K.

is about four thousand square
meters per person on average and

if we produce twenty percent
efficient solar cells on the U.K.

That's really dull place we'd still
generate fifty eight gigawatts of

electrical power averaged over the year so
that's already more than our current

electricity demand now there's a big
problem that it's not produced around

it's only produced mainly in the middle
of the day and I'm not going to come on

to that so there's clearly a storage issue
that needs to be solved with this but

it shows that even just by covering all
our buildings with P.V. we could produce

ALL UP OUR So it's very feasible to
power the world in principle with P.V.

if we gave them farming and
just produce P.V.

electricity we could also power a large
fraction of the world even in the U.K..

So the dominant technology that's been
deployed today is silicon solar cells.

Relatively familiar with them this is
a cross-section of the silicon South Pole

cell it was developed in the one nine
hundred ninety S. And in two thousand and

one which is when the lot of research
sort of spurned on emerging P.V.

and new technologies
the cost of producing P.V.

electricity from silicon
was about twenty times that

the cost of producing electricity
from say burning coal gas I'm going

to come back to the cost of silicon pv
it's obviously reduced a lot since then.

Later on but that's the context of
which I'm a lot of research and

development sort of grown up with
the aim to find new materials that

are fundamentally cheaper and better than
silicon for producing electricity so

I'm amongst these I'm going to
come on to the main topic I think.

Unless the we get to know some there
which is proof sky solar cells so

I'm going to now to sort of talk you
through some of the early steps we've made

with perf Skite.

Seems like something someone playing
around I might try to I'll try to not get

it will just keep the kid if they seem
to not buy fuel for the same type.

So for those of you don't know what
approach skite is it's a crystal structure

that forms a B X three structure and
it's not just any old A B X three it's one

the site forms the saying structure
is calcium Titanite So there are.

Three structures as well but the ones
that form this calcium tightly structure

are typically temper off skite and
they form they look a bit like

this if this was the materials we use for
the semiconductors we use today that black

blob the I can't find is an organic
cat on such as method ammonia moral or

ammonia or form I made any I'm a little
don't here's a metal Cateye and

such as lead or ten and these white X.
and ions are highlights.

Bromine or chlorine.

Just to sort of go through
the history very briefly the first

cesium lead highlight the rough sky

discovered in one thousand nine hundred
two by well sorry eight hundred ninety two

a little while before nine hundred eighty
two you put some time in the past.

And then the structure so that there
wasn't a sudden explosion yes these

are going to be really good for electronic
devices took about sixty years or

seventy years so someone actually
wrote out the crystal structure and

it turned out there are proscribed
cesium lead does make a profit.

Temperature but

it's actually not a perfect Skype
temperature and this is quite interesting

the cesium Catalans a little bit small to
form across guide at low temperature so

there was this some development in one
thousand nine hundred seventy eight.

Which was.

Very interesting where hybrid lead
highlighted Prof Skype's who made using

meth of ammonium and this is methane Money
Lead highlighter methane money I'm ten

highlights and interesting only metal
ammonia I'm is bigger than cesium So

it's bigger than possible with the
periodic table if you want to make this

lead trial I'd perf skite with stuff in
the periodic table you actually couldn't

make a stable crystal at room temperature
that's the three deeper off sky so

I think that's probably where
the importance of the hybrid for

us guys come in it's coming by
enabling us to make a stable three D.

Prof Scott crystal with that iodide that
turns out to be electronically quite good.

A little restive not much activity
till the mid ninety's when MIT seeing

has such a doing.

Measurements on these profs kites and
led to.

This is just one example of a paper they
published where they saw a semi conducting

to conduct a transition changing the
Cateye in in the tin hate tin triad for

off sky from a small caps
onto a large cast iron.

And then the first solar cells with these
materials were reported in two thousand

and nine by Tommy a sucker and
his post took care Okajima

they basically were working on Dyson style
solar cells they took opposed to electrode

and usually this material is going to high
surface area it's usually observed and

has diodes up to the surface
it absorbs the sunlight and

they replace the dye with perf sky
not I crystals by mixing now and

let iodide dimethyl ammonia Myatt I
don't lead bromide a method of money and

probably might in a servant then spin
coded on top of this porous film not for

a middleman I crystals
they integrated this into.

Satisfied by filling it with a redux
active electrolyte a managed to get

working solar cells at about three and
a half percent efficiency but

they were very unstable I lasted
literally a matter of minutes so

no one really followed this work very
much so I did I did Japanese U.K.

ground I'm with with a not
actually with Tommy a sack of.

A commie who is one of Tommy's ACARS
colleagues so I sent a student out back so

I thought to be quite interesting to try
these profs kites in solid state dye cells

are replacing the electrolyte with a solid
state peach I poked conductor so I sent

Mike Lee My student out there and by the
time he got there could Jima had left and

there was no activity in proof Scott's
before she they managed to track him down

in a bar in Tokyo and this is the starting
point for the press cards and

this is the recipe written on the back
of a big amount Luckily Mike had

had had the intelligence to take a photo
of it because I think the subsidy

got lost somewhere later on in the evening
but basically this is does tell you how to

make festival mixing metal I mean with
hydro metal a metal a man with hydro

make acid to make metal
ammonium hydro bromide and

then mixing the lead bromide with
the method ammonium hydro bromide Dymo

ratio of one to one into
a solution of D.M.F.

to Spin Co You can apparently
get a yellow film so

this was our starting point and

somehow quite miraculously within
a matter it actually took about a year or

so in two thousand and ten they these
things really work well in solar cells so

what we found was the brunt of
the current voltage curve for

Skype from the new LED try I died
infiltrated into poorest T.I.

to use in a solid P. type or conductor and

the efficiencies we got up to around
seventy percent efficiency and at the time

this was much better than the efficiencies
we've ever had with dice with this.

Structures that worked very well but
what we found was we could replace

T.-I two thirds and then type charge
conductor with alum in your mock side

that's just an insulator and we found
the sound improved we were just doing it

at first to probe whether we had transport
through the proscribed phase and

actually the notable difference is
the open circuit voltage the voltage your

which would generate hundred zero
current increased quite considerably by

a few hundred many votes sometimes
three hundred eighty volts and

this men are fundamental messes in
the solar cell just got a lot better so

this was a big step up and briefly explain

if we're looking at fundamental losses in
the solar cell for solar absorber we've

got a certain band gap the vantage we can
generate in the solar cell always has

to be a little bit less than the bandgap
because early photons we observe excited

electrons the energies above the bang they
families down to the bandgap and then you

lose a little bit of energy you got to
extract the charge as well so in the best

solar cells you could possibly make you
lose around three hundred million volts

in Silicon Valley's about three hundred
mill evolves and in this relatively

rudimentary cell we're only losing about
four hundred fifty million volts so

it's getting very close to crystalline
silicon whereas previously we're losing

about six hundred many volts or more so
it's sort of a measure of improvement.

The next steps we made for would.

Notice that is we think
Lumina Lab This is a slab

in fact I'll just step back on
the structure we thought we had at

the time was a film that's made of
pearl asylum and you mock side and

it's good proof skite presumed we still
need to needed prosody and we thought we

needed the whole transported to Filin so
we'd end up with what's basically a bank

Tetra junction between the proscribed
in the P. type home transporter.

In optimizing the devices we tried fitting
the alumina to see how to improve it.

And went right down to number Lumina and
what we found was actually as we

thin the illuminate this is
a cross-section the device

the photo current increased considerably
so this was rather perplexing at first and

actually required us to reconsider
how we think the cells was working

because in the cross-section like this
we can see there's a solid proof Skylab

the observing light and generating
charge and the charge is getting out so

what that means is we do not need a
bulkhead for junction in this instance and

in fact it seems to be operating very much
like a thin film conventional thin film

semiconductor even though it's relatively
easily processed at low temperature and

we took that one step further and
made a genuine thin film device

with physical vapor
deposition starting with.

Peter I forgot to call conductor and a
metal electrode and these over the course

of about six months of optimization we
managed to get these ones up to around

fifteen percent efficiency Reidy
pointed out very clearly this material

operates as a thin film absorber so this
was really the transition we made from

what started off a small man I crystals
in a sort of a bulkhead junction approach

right through to the thin film technology
and of course now the important

parameters are how do we get is nice
electronic perf sky is possible and

get it well crystalized what do we contact
with contact with on the end type side and

the side to assure we get good
charge extraction no leakage and

maximize our voltage at those
interfaces and minimize losses.

So this is the basic structure we have
which is the F.T. conducting oxide and

then type of charge conduction led pull
selectively pull out electrons and

block calls the proscribed absorber the P.
type conducting lead to pull out holes and

block electrodes electrons and then
the electrode so before I move on to now

going some sort of details in some more
recent work I'm going to just going to.

Briefly talk about history sis
improve sky solar cells it's a piece

peculiarity but it's a period we've
had to address which is when we scan

from from furrowed bias to short circuit
to measure the current trace and

then scan back from short circuit
to forward bias we don't often get

the same cab and this history says
it's there but it's not simply

if we slow down the scan right we
often still have the history says.

Now if we sit at a fixed voltage we find
the current rises over time like this and

it gets to the point on
the reverse can J.V. But

the point it stabilizes can also move
about quite a bit so there's some weird

phenomenon going on here that we need to
understand we've done quite a lot of work

on it in terms of understanding it and
I'm We recently developed a.

Numerical model adrift a fusion model to
try to explain it I'm going to just now

try to explain the results of this if you
want to ask more questions on the details

it's probably best actually afterwards
that he even after the Question Time.

Maybe after I fly back to England
because it's quite complicated.

But I'll just tell you that results so if
we look at the left what we find out that

we need we need traps we need electronic
traps and we need money by lions

if we run histories as we don't want
history says but let's say we do for

this purpose of arguments so
we go with the conduction band and

the valence boundary got holes and
we've got to electrons if we apply

a negative bias to the sound
what will find is that and

just leave it there will find
the negative ions will move towards

this left hand side and this is the side
you want to extract electrons and

the positive ions will move towards this
this side when the negative ions move to

this side they will be stabilized with
the accumulation of positive space

charge in the valence band so now when
the electrons come towards the interface.

And trapped in the sub gap states that are
very quickly depopulate because there's

a large density of positive charge here
and then we'll get very rapid trap

persisted recombination Now if we apply
the bias in the other way this is forward

biased towards open circuit what we do is
we push the positive ions towards the end

type side these that if there are positive
Onyx pc's negative ions towards a P.

type side and these positive ions
stabilize a large density of negative

space charge and
they repel positive space charge so

what happens is the electrons will
trap into the traps that are there but

these traps run depopulate because there's
not a very high density of positive charge

near this interface and
then there are once these traps of full

the material doesn't see any traps anymore
so operate as if it's got no traps so

by this mechanism we can explain the fact
that the semiconductor seems to be in

a good state when we first biased it and
in a bad state when we reverse bias it so

to sort of summarize with diagrams to
get history says we need to have both

my by lions and traps and what we found
was if we had if we had just traps or

just money by lions we couldn't replicate
history says the J.V. Cubs so so

if we get rid of the most bronze all
the traps we can get history says for us.

So the next things I'm going to talk
about is the means by which we can limit

the defects or limit the traps in the
solar cells now we Chris lies these probes

guy films typically from solution but also
from vapor on top of the substrate and

the substrate influences how the films
crystallize we believe well we don't have

that much evidence for it very much
influences the defects in that in that

material at any type collection there and
this is some results where we've taken

compact E.I.O. two that we usually use and
we functionalized it with a firm or

in self assemble monitor with a car
bookseller cast it on and see.

Well the difference is we find in the J.V.

curves that compact here two has very
bad history says was the ones with

the following a much reduced and then on
the right I show the stabilized efficiency

is a function of time where the fully
modified surface is very much more stable

than the one with the bad two So what
this shows is just by small changes well

quite dramatic radio going from
a parallel oxide to a number.

You can have a big improvement in this
history says and it also asks the question

as to whether crystallizing the proscribed
on a normal surface is potentially

very good if you think about the T.I.A.
to where you've got to take an oxygen ions

and highly polished surface they're going
to interact with the proscribed ons

as they're crystallizing So they're
very likely to in juice some defects and

some disorder that interface wears on the
organic planet and again this is simply

hypothetical we have no direct evidence
we believe the material crystallise.

Perfectly and would be less
into food because it's just got

these in essence a non
interacting surface.

We can go slightly further and make
cells this is an inverted architecture

with P.S.S. and other conducting
polymers the P. type and P.C.B.

M. is the N. type and these cells
exhibit very very little history sess so

it might in part be due to the traps that
are generated being electron traps and

if we make the cell where the electron
collection layers at the top

may be preferential for
not having defects of that interface but

again it's also that we're crystallizing
the proscribed on an organic

material that seems to be preferential
to an inorganic material and

the cells around seventeen of
percent measured efficiency and

they stabilize it to this one
seventeen point four percent so

very similar stabilize efficiency
to the measured efficiency.

I'm now going to talk about
some deposition methods and

how they influence the south Foreman's
on this crime interesting method for

making proscribed films.

First introduced by sea off from
Korea where you deserve the souls

in this instance I think it's method money
mind I didn't let on that I'd been D.M.F.

and spin kind of the film while spin
coating you drop some tar you mean on

at a ninety seven very quickly and
it causes the poor sky ions to

sense the ions in the solution to
crush out a solution very quickly and

you get a film for I mean that hasn't yet
crystallized but rather a sense of

crashed out on the suit on to
the substrate to make a solid film and

then on the nailing it crystallizes
into a nice relatively uniform film.

We looked at this route with different
compositions of the starting material so

here was starting from a stroke a metric
ratio of methadone I knew my dad to lead I

had I'd like C. O. Ked it and without
the telling dripping you get the sort of

needle right structure is that all very
uniform and there's lots of holes between

them with the totally rain dropping you
get much smaller crystals but they're very

very much more uniform without pinholes
if we go to an excess organic cattle and

put three tons of metal money Miah died
this slows down the crystallization

we get bigger grains that are a bit rough
without the tolling dripping with Tony and

dripping we get a film that looks better
but it's still got some pin holes in it

and we can go to another room where
we start with lead clear right and

three times method of money Maya died and
this basically gives quite a lot of nice

of films what happens here is we basically
produce methane a monument I'd try and

died and lose tomorrow as of method
money and chloride on heating and

crystallization but

this just to illustrate the differences
with the different composition and

the different dripping the different
methods for producing it and these

are some sort of I wouldn't say color very
I don't ever use the word colored folks

they're brown brown and right for us I'm
black and white images but this is just a.

Well you what actually happens during
crystallization because it's relatively

interesting if we take this three times I
may I to lead clear eyed route where we

find is when we first start crystallizing
when you create clear crystals so we could

with some precursor compound it is there's
a next hour deep out into it and then

this slowly turns into the brown paper
off sky if we do the totally rain drop

didn't drenching with this we find that
we instantly form the clay crystals but

at the same time the brown profs crystals
and what appears to happen is the brown

proscribed crystals a crystallizing within
the the precursor Crystal as it grows it's

more homogeneous and
gives much nicer films.

As a nother root by Kunin
the composition of the solution

by mixing in different some
ounce of lead iodide and

lead chloride in and few different
tweaks we can actually get a system

where straight away after spin coaching
we've basically got perf skite crystals

nucleated instantly on the substrate and
then when we heat these they coalesce and

form very nice compact films with very few
pin holes and you see now they're starting

to have real Crystal facets and
structure to the films and these devices

are actually getting up to around nineteen
percent efficiency on a standard T.I.A.

to layer with M.P.T. with a tad on
the back and stabilizing it around

seventeen and a half percent efficiency so
let me a little bit of the way that but

understanding what we can see here is that
we need to nucleate sites that grows these

new creations of two spots then
is like is the crystal grows and

eats out the remaining ions in the in
the image first material let's say

then before they impinge on each
other then we'll have pin holes

if they're too dense dense then we
just have very small crystals and

lots of grain boundaries so it's a balance
where we want them homogeneous and

separated enough so they just me.

In the latter stages of crystallization.

I'm now going to talk about a few a few
other things related to heterogeneity of

the system so if we do some piano
mapping of these films they're not for

a uniform so we like fed him
an essence is a measure for

the quality of the semiconductor
because what it means is electrons and

holes a recombining radiatively is the
recombining radiatively we don't want it

to operate as an early Di but a very
combatting radiatively it obviously means

that not recombine in normal radiatively
and the norm radiative channels for

instance trap persisted re combination or
other recombination mechanisms mechanisms

that we don't want so in principle we
want the film to be completely and

homogeneously bright and that's not what
we see we see some grains that are very

bright some grains that it darker in the
grain boundaries they're very doubt and

if we look at the time resolve P.-L.
decays in these different regions

we see we get a nice long lived slow
recommendation on some grains of fast part

and really fast of the grain boundaries so
clearly there's a heterogeneity we need

to sort out we need to find
out what's its origin and

how can we resolve it.

This is an example of some of the some
of the work we've been doing.

Things very interesting about the profs
guides but a peculiarity as well and

the challenge is the realm of impurities
in the material sometimes we find the best

devices made with very impure material for
instance our lead chloride is ninety eight

percent pure and we don't know what the
other two percent of the material is but

if we don't have it the sounds
don't work so well.

Thing we noticed imperfectly was that when
we take metal ammonium iodide if we re

crystallize it that's a standard
purification method the film's run is good

and the SARS runs is good and we were
looking into what impurity could be that

and what we discovered was that high
powered phosphoric acid H.P.'s.

Is used to a stabilizer N.H.I. and if we
take the rechristened allies there may I.

Rushed out if we just
take the dried M.A.O.I.

there's still some H.P.A.
left in the solution.

So what we can see in the absorption
is they look similar to

the control film of the one with H.P.A..

And this is the absorbance on a log scale
you still can't see much by eye but if you

fit the slope of this scale what we find
is that gets a bit steeper with the H.P.A.

treatment which means
the back energies less and

that's a level of electronic disorder so
the H.P.A.

seems to have improved the electronic or
reduced the electronic disorder and what's

very noticeable is the photo luminescence
of the films increase in intensity and

the lifetimes go a lot longer there's
still a fast component so looks like this

still ahead Trojan eighty but it's
better than the film without a G.P.S..

And if we look at the P.R. mapping it we
can see it's got a lot brighter there's

still dark regions it's probably only
fifty percent homogeneous let's say but

at least it's on the way and
the solar cells are a little bit better.

We took improved proscribe solution and
put it into a back into the inverted

structure which is a whole
transport of metal monument.

Here we've used B.C.P.

and so on for the tend to give quite good
contact that's a cross-section of it and

here again in this structure that controls
about seventeen percent efficiency and

we managed to get up to around nineteen
percent with the H.P.A. treatment and

again the stabilized power output pretty
pretty nice actually a little bit

lower than the measured J.V. curve so
we're trying to work out right the sort of

between eighteen to nineteen
percent efficiency.

So we just take a step back and look
what's happened over the last few years

and the fish and see the prostate
cells is sort of rocketed up there

some people reporting over
twenty percent sounds.

He keeps reporting twenty four percent
sounds but that hasn't been published for

yes I read.

About the legitimacy if you put
it I should say that this is.

He gets very very.

He gets very high open circuit voltages
which suggest no losses which will be

fantastic so I'm sure we'll get and
maybe some people have got there already

very soon we're going
to touch on silicon and

maybe even push past
towards gallium arsenide.

So can we take on silicon.

Do we do we just take on this.

Becoming a juggernaut of an industry
with a much better technology that's

challenging if we look at the production
of silicon we might think it's possible

I'm not going to go through it but
basically there's a lot you start with

sand definitely abundant and cheap but the
problem is you've got to process it a heck

of a lot not a temperature lots of
chemicals do a lot of manual stuff car to

get well shit and that with a rifle
then after you've got the wife or

you've now got to turn this into a cell
which is a hell of a series of events.

If you look at the proscribed solar
cells in principle they should be much

much simpler simpler we
start with the yellow powder

mix it with the right powder in
a solvent that's like all right.

We then basically go down five or

seven layers for the simplest means as we
possibly can and then up with a finished

pan a little bit of laser interconnect so
the cost of this should probably be about

half the cost of a silicon module in terms
of cost per square meter simply because

first solar modules are about half the
cost of the thin film technology it could

even get down to allow us of the fission
Cs high that should be a winner but

of course Silicon has got a distinct
advantage it's been around a long time and

there's been a massive scaling in
the industry so in two thousand and

one I was saying the cost of silicon P.V.
was about twenty times that of

a conventional electricity
the dollars per peak.

And eight dollars per watt peak
now the cheapest price for

silicon something like thirty cents per
peak for a module so it's come down and

down in price and there's nothing really
stopping that getting lower the efficiency

of the cheapest modules is around fifteen
to sixteen percent efficiency but

there's new technology silicon
technologies coming through

that approaching that up to twenty
percent twenty two percent the cost per

square meter will probably even get
lower as the new technologies come in so

the dollars per watt might get down
to fifteen cents but will be so

how do we compete with that
with the growing scale.

And just to sort of illustrate that
before on a sort of timeline going back

to one nine hundred fifty S. which isn't
actually that long this is the cost of

electricity from different sources and
you can see solar P.V. just plummeting and

in fact is probably going to get cheaper
than power from any other source

in many locations very soon this
is a sort of predict projection

not mine it just took
this off the Internet.

Story with no permission probably.

Thank you.

Some some installations I think a first
solar installation someone New Mexico is

six cents per peak That's right there's
been some silicon installations in the USA

for four and a half cents per kilowatt
hour which is significantly less expensive

than the cost of producing electricity
from gas ready so even in the U.K.

We could even in store for close to
close to ten cents per kilowatt hour and

there's this scales it's going to come
down if it just keeps losing sixteen

percent in cost for every doubling in
scale then if we start to produce more of

the world's power by P.V.
it's going to become more cost effective

now the big caveat here this looks great
maybe we should just go home and stop.

P.V. it's done the caviar is that this is
the cost of producing electricity from

sunlight and the sun doesn't shine twenty
four hours a day you can't turn it on and

off as the demand changes so

clearly what this has to do is also
accommodate the cost of storage and

redistribution which is basically going
to be filling in the six to bit but

if we can get down to two to three
cents per kilowatt hour for generating

electricity then in principle that will
be able to accommodate the storage and

that the storage costs are coming down as
well so it's almost inevitable that P.V.

will work so what do we do with
the new technology Well the good

news is Peavey's probably going to be a
big market so there's plenty of space but

can we actually you know a neighbor
list to happen happen faster and

what we think we can do is basically boost
the silicon so not try to compete it but

try to make it better by putting Pearl sky
cells on top in the first instance and

this is an illustration
of a tandem solar cell so

silicon solar cell will produce about
point seven volts open circuit voltage

under full sunlight and it would generate
close to forty million current so

that gets you sort of twenty
five percent efficiency.

As we can generate up to around one point
two valves and we can chew in the bank

precisely half the sunlight was
going into the silicon cell so

if we simply say we had a twenty
percent silicon cell at the back and

a seventeen percent per cell on
the top we get an extra ten percent

efficiency from the silicon half of what
was the silicon was generating on the full

side sunlight so that would give us a
twenty seven percent efficiency cell where

is the silicon on it's own as I said is
only twenty percent efficiency said gives

you the prospect there for a massive boost
even with just a seventeen percent of

that can be manufactured at scale at that
efficiency this will make a big difference

so where are we I should just say there
are a lot of groups now working on.

The some nice papers from Christoph
Ballard from for me P F L and C S C M N

might McGee here in the papers being
published all the time on this we've

been working on it ourselves this is some
work that we've done in my research group

in town in Oxford and we've basically been
working on Spotty coaching Nike on our

profs guys how to get good semitransparent
see this with method of money and

lead try and died and
what we find is if we put our complete.

That's not an ideal choice it does absorb
quite a bit in the I.R. spot acknowledge

it right here in the total sound we
can we can get a residual efficiency

of seven point three percent from the
silicon Soule It was a nineteen percent so

and if we take the trend semitransparent
efficiency of the proscribed sell at

fourteen point four we're up to twenty one
point six percent so it's a bit of a boost

Unfortunately this has got quite
bad history since we got Perth.

So it's only stabilizing at eleven and
a half percent so

that gives us about eighteen point
seven percent so about breakeven so

even with this relatively rudimentary
design already breakeven on the silicon so

we're using with good
prospects to move well beyond.

This is some startup company also P.V.
this is a genuinely integrated

to terminal device where the process
is being processed directly on top of

the silicon sound silicon so it was
about seventeen percent efficiency and

we've managed to boost that up to just
over twenty one percent so it's not

the twenty five or twenty seven percent
of this clearly some work to be done but

it's quite nice in a solar cell with one
point I've also been circuit voltage

current around sixteen million so this
could basically be pushed up to around

nine hundred twenty million if we can
get the voltage up towards one point two

votes in the factor up to point eight and
that's a thirty percent so so

that is feasible and
clearly requires some work.

Before I.

Move on from town themselves I just
want to talk about shooting the bandgap.

What is the time I'm good so

in terms of the proscribed fairly flexible
so we can choose the ions we can tune

the lead from lead to ten we can chew
in the countdown for my Medea method

ammonium cesium very interesting we can
choose between iodine umbrella I mean and

this gives us a really good flexibility
on the band got from the absorption

you can see here we go from something
that's about two point three right out to

something close to one point four Evie and
what this means is we can chew the bang

up to try to match it perfectly to
absorb half the light in silicon and

this is a bit of a sort of a sneak preview
of some stuff that we've only just

submitted but
I've managed to get a point seven three.

Are working pretty well where we generate
hundred nineteen million current out of it

and if we put a semi transparent
electrode on this and

stick it over silicon so we get about
seven and a half percent efficiency so

this gives us a terminal equivalent for
the I.T.O.E. cell that's fifteen

percent efficiency for term of
the quibbling over twenty two percent.

We got a bit of a loss involved going
from silver to right here so the hope

is will be able to recuperate that in very
soon actually have four terminal cells

over twenty five percent efficiency the
still somewhat the same engineering but

the material seem to be able to do it and
then if we can integrate this new

composite into a full terminal to terminal
sell then we could potentially move up

towards that elusive sort of breaking
twenty five percent up to twenty seven.

So the last few things if I have time
I want to talk about a related to

stay billet.

So when we first found this
material worked really well

I was extremely excited.

Simon with this as to whether it was
radio acting like a solar cell is a some

chemistry going on is the material
degrading Is it correct.

It's really photo countermeasure And so
when the first things I got my student to

do was to take a film of proscribed
laminated between two sheets of grass

put a proxy around the outside and
stick it in the solar simulator and

leave it there for as long as he
could keep measuring the observed and

just checked as the material totally
disintegrated was there and I was actually

surprised to see the absorption barely
changed it told over a thousand hour

time period so that was that gave us quite
good confidence I thought maybe this

really is something that can work but
of course going from a film lasting for

a thousand dollars on the simulated
sunlight to a stable solar cell is another

matter and in fact the things we need to
worry about for some results they've got

to be able to operate up to eighty five
degrees down to minus forty they have to

be a significant exposure they have to
cope with eighty five percent humidity it

id five degrees and a whole series
of tests and be stable so I'm

going to talk you through some things that
could potentially be instabilities and

some of the things we've solved.

The first thing this is a phase diagram
for methyl ammonia lead try I died.

Is a function of pressure if we just look
at the left hand axis because we generally

are atmospheric pressure a low pressure.

We've got a tetrad know it's a cubic phase
transition that should occur around three

hundred thirty Kelvin which is about
buying you know operating window sixty

degrees seal there about if this happens
there's some theoretical calculations that

suggest the bangup should drop by about
three hundred million that could be

critical for the solar cell into race when
we suddenly go from A to right to get

material that could stop it working
secondly if there's a volume change then

that could be catastrophic it could cause
stress in the crystal and it could die.

So what we did was we looked at the piano
a Mission Peak as a function of increasing

temperature and reducing temperature and
what we found was actually it just shifts

to higher energy and back again we
don't see any obvious sign for a big.

Engine the phase transition if we if we
just take the peak position as a function

of temperature we see some
change in gradient of change and

around the temperature we expect the phase
transition to occur but it's not abrupt.

And there's certainly not a big change
in Bangor we expected go to lower energy

that illustrates a change in volume so
that looks OK and in fact this paper

the rubric we did for with Philippe Daniel
is comes up with a theoretical explanation

to this whereby if you freeze
the proscribed in the cubic structure and

calculate the bandgap you get a bang up of
about one point three electron volts but

if you let it also light through thermal
vibrations what you find is that

the band got Spacey governed by this till
time go between the lead in the eye again

bones if you've got a heightened tilt
town girl you go to a wider bangup and

in the calculations what they found was
that three hundred twenty Calvin This is

the average till time goal of the lead
I had in bond is that the average is

in the cubic face but actually if you take
a snapshot at any point it's very rarely

this very low probability of finding
the tilt angle of zero so what it

means is that actually the crystal is also
lighting on either side of the cubic and

it might in principle
on average be cubic but

in reality none of the Bangles
correspond to the cubic So

that sort of explains why we don't see a
change in banged up and also explains why

there's not much volumetric change
the other and other issue for stable it

is thermal stable ity if you take a film
of methane ammonia Maya died and heat it

at eighty five degrees in air it turns
yellow so that doesn't seem very good what

happens is it turns to lead iodide which
is one of the starting components and

basically we've degraded and driven
out the method ammonium iodide excess.

Fortunately there is one of
the cast iron that seems to.

Kids confirm I'm a did him and
I mean slightly larger and less volatile

the metal ammonia and this is much more
family stable so these films for instance

are heated one hundred fifty degrees on
a hot plate in there the method of money

might I do with an alligator is yeah
like this stuff stays stays Baikal stays

dark and we've done a lot more extensive
tests this is visualize it quite well so

this stuff one firmly degrade till it's
about one hundred fifty degrees whereas

even in nitrogen this stuff will start
degrading at eighty five degrees.

So firm I did Me I'm appears to be a
solution but it's got its own problems as

well I'm a firm I didn't is
slightly too large to form a stable

would let iodide room temperature and
it tends to want to make a transition into

the more thermodynamically stable number
of sky structure that's basically one D.

chains call an edge sharing lead I
had I don't and that's yellow and

not very good semiconductor But
again but just by tuning the ions and

tweaking around a little bit we can get
the material to stay stable at room

temperature and these are this is an
example of a film that's been cycled fifty

four times from plus eighty five to minus
forty and the absorption hasn't changed.

Just come back to the hydration issue a
moisture sensitivity the mechanism this is

a paper that's nothing to do my work but
it's a nice illustration of this is this

is this is Crystal when it becomes
hydrated you can you crystal structure and

then you can hydrate it further to
get a third crystal structure and

when it's in this model hydrate or die are
dry firm you basically can firmly degrade

it very easily it is reversible but if you
put any heat in in this case then you can

degrade it and that's the process that's
occurring that needs to be stopped so

the solution are for instance you take
your whole transporter usually you

spot them a tad and you something that's
much less hygroscopic a much more dense.

With you opinion polls this is an example
which is P three h t rap single

carbon nanotubes in the P.M.A. Matrix
it's bit a bit of overkill I don't think

it's necessary but this is stopping
the thermal degradation even from F.

ammonia like triad I'd.

The other route is to encapsulate it this
is somewhat from Oxford P.V. on films with

different laminates we've been through
laminates that are used in the P.V.

industry and selected ones that
are good enough to stop our sort of

visible degradation occur in eighty five
degrees eighty five percent humidity so

without an edge sealant as
well they're pretty good so

they seem to be resilient enough.

And.

The next issue we have to worry about is
U.V. light if we take a means of porous

to so I'm with filled with white
light on it which is generated from

the thing seems quite stable but as soon
as you put U.V. light in that you find

that the Fed of current drops off
very quickly within a few hours.

If you put a U.V. filter on it's
slower but it still degrades.

Firstly by swapping the poorest
T I O two with with a solution and

we found we could stabilize the photo
current quite a bit this is on the U.V. So

this is lasting for hundreds to thousands
of hours versus just a few hours but

it still degrades a bit and then
finally replacing the compact here too

with an organic C sixty basically
stabilizes the photo current SO

choice of electrodes very important not
just found it crystallizes the Prescott

but also fits the resultant
impact upon stabile ity.

And this is just some
results from Oxford P.V.

on some of their cells this is
actually a few generations ago but

here they are lost in for a few thousand
hours sixty degrees under full sunlight

and I'm delighted another thing we noticed
and IT people in the existing P.V.

industry and know this already for
a less hours if you write.

Under load it basically will degrade
it much faster than if you aged it open

circuit or short circuit so
we need some of the issue.

Under open circuit then we found when
we went to light we were still getting

degradation so important thing
is that we've got to basically

make the stable on the light
these cells are on the light.

So.

I think I'll probably more or less finish
that I just put up a few slides on

ten Prof Skype so we are interested
in replacing lead I think that is

probably perfectly fine for the solar
cells of this good recycling policy and

that encapsulated Well I don't
think there is really a risk of.

Leakage and the toxicology risk
of that dealt with properly but

other metals could be very interesting and
specifically ten if we look at the P.R.

position here for the lead has shifted to
much lower energy with the temper of sky

so what we think this will give
us the opportunity to do is make.

Themselves and these solar cells work
they're not very good so far the best

efficiencies around six percent efficiency
so long way off the lead devices but

what's really quite surprising
even in these pretty so

I say the best is six the average is zero.

There's quite a spread even in the cells
that are pretty poorly distributed

advantages quite remarkable that eight
hundred eighty million volts the bank

gets one point two either Evie so they
could give us a voltage loss of only three

hundred fifty million so actually the
voltage loss in the ten cells is even less

than in the red cells so we've now
increased our effort quite a bit.

Over the next six months or so we actually
start to make probably efficient ten cells

and they may even get better than the per
the lead ones if we're if we're lucky

there is a critical state billet issue
with the ten the ten to dispute takes

into to infer plus very readily and
understanding if it is going to be.

Feasible to stabilize that and how to
control that is a critical challenge.

OK So with that I will find my research
group I'm out of find funding sources and

collaborators who some of the work I
presented was in collaboration with them

and thank you very much for
your time and place to.

Thank.

Yeah.

Well we showed by putting the C
sixty which is an electronic scepter

at the interface so we can get the same
results every process a layer of C sixty

as well as this self assemble Manoa so.

Yeah yeah.

Yeah.

Yeah so me.

I mean that that specifically why
we're stressing under load and

for long periods of time the cell seem to
be stable now it doesn't mean the ions

the will have been so my own motion
observations so far as if you take for

instance in plain electrodes and
bias the film and

you have that in there and under light you
can start to degrade it to one side so we

think you drive the iodine away and then
you starting to lose method ammonium and

you start to degrade
the material if it's in June or

an inert environment it doesn't seem to
degrade under the measurements we've done.

That I can't think of the prime of his
off my head but it's not testing for

thousands of hours you know it's tens
of hours maybe we've looked at it so

it appears that if they think capsulated
well so if you keep the moisture out

you're much less likely to generate new
defects but of course as we generate if we

do generate more defects because the ions
have migrated then we start to get some

degradation then that's going
to create more mobile lions and

there's also likely to be a relationship
and we haven't managed to measure it and

we don't know how to measure yet there's
likely to be a relationship between

the amount of my Brians and the defects
and maybe that it's the defects that

are mobile it might be that there's
interstitials iodine in stations for

instance that might be mobile it could be
a whole host of species we don't really

think it's iodine that's the mobile
species the highlight but we don't really

like.

Yeah so it's a reducing agent so

we can noticeably see that if we have any.

Iodide in the fill in the solution
that gives a slight red absorption

then with iodine sorry we can
reduce that back to iodide and

the solution was clear again so we know
it does that and we think that what's

happening is when we crystallize in
the film we're generating iodine and

then this is basically
the balance is being kept kept

in favor of iodide by
the presence of the H.P.A.

so.

Potentially yeah potentially it's
interesting the impact it has.

Yeah.

Yeah.

Yeah.

Well there's two things that are different
with pinholes a definitely an issue so

if this pin or with any basics posing
your film where the pin holes is moisture

you can get in and degraded that So
we think probably the primary reason for

degradation rapid degradation
is pinholes in the film and

it's likely that with
the with the it's P.M.A.

which isn't actually that hydrophobic
it's I mean some people think of

it as being argued scopic actually is just
better than the spire I'm a tad which is

the other issue is the spam a tad
we don't do with lithium T.F.S.

I that is hygroscopic and
it's that presence the lithium T.F.

aside that makes it much worse so
if we process a film aspirant out

it's very difficult fire solution not
to get pinhole So even without dope and

we see slow degradation boys still
see Gratian but in principle

if you do physical vapor deposition of
a really nice homogeneous organic P.

type I also expect that to protect
it as well and then in the actual

deployed solar cell on top of the P.
type you then got whatever your contact is

it might be if that's deposited without
pinholes that would be a very good barrier

and then you've got
the lamination foil and

then you've got glass so really the only
risk of stuff getting in is going inside

ways along through the lamination foil and
then down but you've got all these layers

that are protecting it which
which at the same time is key.

The moisture out they also help
keep the organic hay light in so

one of the problems is
that salt can decompose so

in fact methane ammonia lead trial died
decomposes much much more slowly when

it's kept with a good whole conductor and
that's how we can get you know one week's

eighteen at eighty five degrees without
degradation and in fact we've got some

cells that are lost in sort of close to a
thousand hours and eighty five degrees in

air with the complete cell with a slightly
different configuration simply because it

can you can basically keep start the film
from degrading by keeping moisture out and

holding the highlight cells in so
it's got two functions

things.

I don't think I mean people have been very
interested in there's been quite a bit of

work of looking at electricity in these
materials and whether it's important and

of course when we first observed history
says there are a lot of people thought

there was a life photo Fairey voltaic or
some some strange

concept by that is that if we think
at the moment sort of polarized

ability is masked by these mobile ions
we've done some quite careful measurements

looking at the polarization so
it may become important so

this still some people think in
the certainly the dielectric

nature of the material is important for
having a lot of extra binding energy but

what we find for instance going from from
methyl ammonium to form an opinion and

from my medium the dipole moment of that
is about a tenth that of methyl ammonium

then we don't actually see it we in fact
the binding energy is almost the same.

We're looking we're going to we
haven't done measurements yet

of looking at the extreme
binding energy with the cesium

inorganic one which will be
interesting to see whether this.

A significant difference and
I don't expect there will be so

I don't think it's central to the.

Operation but
the diet the dielectric is so

if maybe the displacement of
the lead in the hay like might be

important.

Thank you very much I really appreciate

the talk.

Thank you very much.

For.

Giving.

A free copy.

To look him in the back.

OK thank you very much OK OK.

Thank you Mary.