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welcome to the section on like being induced :colon mapping of organic solar cells my name is me Johnson and I come from the
sort group at the Department of Energy Conversion storage at the Technical University of
Denmark His an outline of
what what I'm going to talk about today on 1st briefly touch
about how we measure characterized the organic solar cells and ways of detecting electrical defects on telling them about the standard the big all like used current technique which is used to map the solar cells and they're not
going to Our improved designed for the instrumentation which is much faster than we have the capability of using multiple wavelengths and we have different mapping types of the organic solar cells and perhaps most importantly we can do what is called contactless measurements that is we do not need to create direct electrical contact to the solar cells in while and we do the measurement and that has altered opt for the possibility of doing rose who rolled their like being induced current met and finally on to round off with an experiment that you can do yourself that holding the do
it Yourself big which only requires that your computer 7 a simple instrumentation on your own ingenuity so the way that
we characterize solar cells normally is by to an mission so we the measure current output of the solar cell while we step through a voltage range and then we get a curved like the 1 that you see From this curve we can estimate
of measure the efficiency of the solar cell the highest voltage you can get out of the cell and the highest character if there are some electrical defects in the solar cells this will be manifested in in the form of this curve but it is only a global information doesn't tell us where in the solar cells the defects are for this we need some kind of mapping techniques and the 1 that we use here In the light beam induced
current technique it is also called the Supreme induced current technique or even an external quantum efficiency man then you get a picture that like the 1 over there and where can see how well the solar cell functions at a given point there is a
3rd and technique which is caught the filmography which measures the heat output of the solar cell and this is now the subject of a separate lecturer in this series but I'll briefly touch upon how the 2 methods are connect
so the standard of big principle is shown here so
we will have a light source typically these the positioned over the solar cell which is connected to a source mission unit so we moved the place sources around to scan the solar cell while we measured the output at
each position from the solar cells so we set the voltage to Surin measure current and the computer then converts the current values at each point and assigns :colon too so if you want to
maps say a 10 by 10 centimeters solar cell at 100 micrograms solution you get about a million .period and if each .period takes about 25 milliseconds to measure if you have time for moving the laser and time for they're getting extracting the current this will take about 7 hours we're a scanner the old solar cell and then the computer then generates and that
like the 1 shown on the right it's a very slow that but useful technique of course and we
initially built an apparatus of that kind of and used it for the from different measurements on the solar cells that we prepared here is an example and where we had some rather small solar cells about a square centimeter and we tested different types of silver inks used for
creating the electoral context to the solar cells the cheap treat different silver Inc's Inkster
1 of which is he and 1 which is usually cured and finding in water based in and what we saw in these images is that the future curating destroyed the solar cell action immediately there where it was in contact With the solar cell while the Uri and cured Inc and worked or so of course based on the images here we could
select the you know curable think and the best ones with this
showed that and it was a valuable tool for extracting information like this here is
another example of the same here we have the same 3 different types of silver ink and In this case the silver electrode has been made someone laughter and so you see the effect of how
the she'd curing think destroys the solar cell function much more readily
To because this technique will show slow but but obviously very useful we tried to find other ways of and to improve this technique would make it much faster than and we have made a new and improved version of the that is much faster than that if you are interested in the no details about this
refer the into this article that we published in advanced optical materials in 2014
the set of a shown here and we still have a place this time it's fixed and the way that we move around the EU that being the light beam is using the mirror that is controlled by 2 motors a fast the rotation in the X
direction scans in that direction then we have a slower rotation in the wider region so we create a sort of rest pattern and the signal is picked up by some
custom electronics that amplifies the signals censored into an oscilloscope what we get
ahold aches skin in a very short time and transfer them to a computer so scanning in
the x-direction is some 2 thousand 500 data points and this takes about 0 . 0 1 seconds which means that the 1 million data points can be there taking out in about 4 seconds to the increase in speed for 10 by 10 per square
centimeter solar cell is 7 hours for the standard they'll be taking in about 4 seconds for the new improved progression or about 6 thousand 300 times here is the
result for a single 1 by late since solar cell and you can see the
photograph of the sale and the top part of the image 2 great electrodes and then you have the Albuquerque image and bottom so Parsifal solar solo works fine it's in yellow the and the bill performing their parts of the solar sail on him you immediately see that that too large areas in the
source so that has some defects in the sun on visible in the photograph and you also see a lot of small at defect .period find
defects along the create Electric which in the resolution the pictures about 100 microns His another exam
assuring that volcanic solar cells are flexible but up to a point 1 all former students crumpled a solar cell then
stretched it out again and performed the ill image of the device and as you can see it is still a solar cell but where it was
creased violently intensity laminated and you can see the way doesn't work anymore so you can see mechanical defects in solar cells would have picked technical you
can have variations in the printing of the solar cells
here an example where we have printed the active layer in the solar cells with a technique called rolled through screen printing then and that gives a rather on leaving the field actively layer film and that is also manifest in in this picture where you can see that there is a great variation in how well the solar cell performance over the
area of the 16 stripes of the initial themselves as I said we
can also image the
solar cells using different wavelengths of the laser and this comes in handy for instance in a situation like the 1 that would have here on a tandem solar cells from 2 different
solar cells 1 on top of the other 1 takes part of the solar spectrum and the other solar cell takes the other part of the show patients refused and places with different
wavelengths you can address the 2 different sets of cells and you can see that there are defects all areas and that not function very well in 1 subset and other parts of India the soap also can use this technique to differentiate between defects in different parts
of tandem solar cells
another very important failure mode in the solar cells is if you have particles electrically conducting particles that penetrate all the layers from 1 electrode to the other this can be very serious and large installations will have high power in Houston an example
of a aberrant through between 2 electrodes to have such an electrical short that has burned part of the solar cell this conference is
also being missed her family like likened in these images he awakens signal from these short just before they burned through the solar cells
here we contrast the firm will be technique with
the doctor locking tomography or thermal graphic images of the same type of solar cell and you can see In the El big that
some of the cells are not working and all 1 of the reasons that this is so is that we have some very serious shorts that create heat signatures in the doctor democracy and you can see the 1 with the images here that this the
shortest occurs directly where the great electrodes cross each other
In this new improved L became a technique that gives us some opportunities for making different types of measurements and aside from the normal big Prince is 1 thing that you can do is called composites and snapping if you look at the
solar cell then we have to electrodes to metal electrodes ,comma on each
side of an active which is a dielectric material this is the way that a capacity is spilled up so we could in principle nationally
capacity the resistance's associated with this and using this the big technique here this is an
example here we have taken in the single pixel in the
solar cell and we then turned on and off the laser rapidly and we passed the ladies and then we'll look at how fast they signal intensity builds up in a single
pixel and how fast and dies hard In this exponential increase and decrease of the signal is related to how large capacity and there is each .period and by having an external variable resistance heroes with the solar cell we
can change the the time constant for this the process you and here's an
example of that a solar cell where we haven't defects it is visible in the photograph but not
visible in the big image directly below it but then we had these comparisons mapping images and you can see by varying the externally sister value we can bring out this defect that we have this
is an alternative measurement methods and that we can use with this Bourassa this leads us to
the next point which is contactless helping In order to stand up to and techniques that we have seen until now we have put direct electrical contacts on the solar cell to make sure that all put officials but you can also imagine another way of
extracting the signal from the solar cells and if it is a time depends signal if we have any
external electrodes and that are situated directly above and below the solar cell they will act as a capacitor and if the signal from the solar
various greatly then this capacitor will
pick up a time dependent this is going by the equations that show here here can see how such
a contactless designed is realized we have a sketch of the 3 solar cells placed in December will we have the capacity plates above and below the middle cell and if we then have a time-varying signal that occurs when we shine the ladies on the solar cell then there the external electrodes will pick up signals from the solar cells if we look
at a single trace across
the solar cell then in the standard mold will we have direct context the signal will change from a 0 value when the leases not situated on the solar to a higher level when it enters the solar cell and then it would disappear again when delays in the use of solar cells in the contactless
mold capacity bold then there would be a very rapid changes as soon as the laser hits the solar cell then this signal would die out again because there is no change in the output of solar cell and then when we leave the
solar silicon that will again PA and rapid change so a quite different way of thinking
given the the image and here's how it looks like like we have again at a photo of the so Rosalind top we have the normal Olympic image in the middle and we have the contactless image and video that and you can see that we can actually extract the same type of
information the 2 types of of Olympic we still conceived the union large defects and actually this moral pinpoint defects highlighted by some kind of shadows so this
new contactless technique has actually opened up some new possibilities so we can use it as a characterization techniques for organic solar cells which are produced rolled to roll
and it would immediately give us some information about the the coaching all printing process that we used to to make themselves and perhaps correct for this to
happen and we need to be able to measure the speed comparable to the speed that would choose the cells that is
about 10 meters per minute so the main problems that we have had them onto knowledge to make electrical contacts to the following this we have now eliminated in this context miss the version here
here we have shown the instrumentation that we use in the rule to roll the
instrument with the aerobic installed on top of it and we have the 1st version that we use with dialect direct electrical contacts and you can see the
4 of them moving inside the other artists here then we moved
to the contact list assigned to see a small picture offered here and we have a 30 meter stretch of solar cell fall with about 100 16 modules that we have an image with this conquer contactless helping mold here and you can see that we
can pick up the indicted defects in the solar ourselves that we can get and then used to to take out the solar cells will correct them and the way that we produce
them finally I talk about a do-it-yourself big experiment that you can be conducted home if you want to you only need a computer with a sore cell and able leader to connect the voltage to the solar cell you create a black screen on the computer and paint for instance and put on a white dots that you can move around then you for each position of the white dog you note the voltage output of the solar cell
and when you have finished and the procedures to prevent translate this voltage value to some Colorado and you then constructed an image force ,comma image of that
no way you can make your own intake experiments
and and there that this actually
works while a fine if you make the White spot very small it takes a very long time and then you create an image very similar to the Olympic the image that we get from our instrument but of course it's a much more cost image but you can see larger structures such as for instance that the strike is that we have in the solar cells the areas
that work the and you can see lots of and today the
resolution that you can
get out of this can of course be varied by making a small spot than it takes much longer to get the images if you're interested in further details and this technique you can look up this article and that we wrote together with some of the people who inspired it in energy technology in 2000 and 13 and
finally say thank you for your attention and acknowledged the financial support from the European Commission 7th Framework Programme and through the project of cleaned for you thank


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