hello and welcome to technically speaking a podcast where scientists and engineers come together to chat about a common interest share knowledge and satisfy some curiosity i'm Aneeqa and in this episode i'm joined by Jennifer and Laura to talk about solar cells and their sustainability so to start off with jennifer why do you care about solar cells and what's your interest in them i personally have a background in research i used to characterize perovskites that were
mainly used for solar energy applications awesome and laura what about yourself well i've never worked with them i've heard a lot about them at material science conferences that i've attended and i really like the idea of my house being like completely self-sufficient and generating its own electricity but i've not really been entirely convinced that i could do that with just solar panels alone and my bills are quite low anyway so buying more technology for me
doesn't really seem like a good idea if i want to become this amazingly carbon neutral completely self-sufficient sustainable household that's the dream right i think for a lot of us and especially with the electricity prices are going through the roof at the moment so maybe there will be a kind of tipping point in the future where it would be kind of more cost-effective in order to be able to do that before i go completely off on another uh tangent maybe we can start with defining
what is a solar cell laura do you know what it is there are solar panels that people have on their roofs they're made of quite a few things but the what i've heard about at conferences was the important bit is this um the semiconductor material that's usually made from silicon okay so that's the bit that conducts electricity when sunlight shines on it and apparently apparently it's called a semiconductor because it conducts as much as an insulin an insulator
but not as much as a conductor which i find a bit of a circular definition but there you go ah okay so i i never knew that actually so traditionally solar cells are made of silicon what why why does it because there is because they're a semiconductor is there any other reasons i was trying to read into this before and it's definitely not my background and it's not something that came up in the materials science conferences that i remember
but there's a limit that i think was calculated by two people whose names i'm not gonna pronounce cause i'm not sure how to pronounce them they define this limit using um what's the wavelengths of energy coming from the sun what's the the different wavelengths of visible light how can you absorb as much of that light as possible and what other effects do you have to account for and there's something called a band gap in the semiconductors which is the difference in energy
between the electrons that are really closely bound to the nucleus of the atom and then the ones that are further away the electrons that can move around the so-called valence bands that band gap is um to be most efficient at turning photons of light into electricity that band gap is about 1.1 electron volts which is what pure crystalline silicon gives you that's why silicon i think it's also one of the most abundant elements on earth so that that's handy we're not having to do a lot of
say a lot of refining we're not having to look really hard for silicon we can find it pretty much anywhere and then it just needs to be purified to get it really really pure awesome it seems a bit of a wonder material that you can use it for solar cells we also have silicon valley where i guess they make the chips and computers from them i don't know because again this week i was watching another k drama and they go to silicon valley in that one it's called
startup great drama if anyone wants to watch it okay so silicon is kind of the conventional conventional material jennifer you mentioned something called perovskite at the beginning which we used to do work on is that another type of material that we can use to make solar cells yes it's another type of semiconductor material a lot of people haven't heard of perovskites most people know about silicone-based solar cells it's not surprising since the potential of using
perovskites as light absorbers for solar energy applications was first discovered in 2009 so that's not even two decades ago the researcher who led this discovery was miyazaka and the efficiency of perovskite solar cell devices at this time was 3.8 and six years after this first discovery of the perovskite solar cell devices the conversion efficiency reached 22.1 this kind of increase hasn't been seen with any other type of solar cells including silicon but i mean that
might be due to technological and advancements in research i mean the first uh silicon based solar cells were produced in the 1950s and technology has come a long way since then that's crazy and is 22 good or do we need to have higher if we can use those uh instead of silicon that was six years after the first discovery but nowadays it's uh on par with silicon at least for single crystalline uh silicon so or single crystal silicon so perovska solar cells has an efficiency
today of around 25.7 percent where a single crystal silicon solar cells have an efficiency of 26.1 so there's a difference about of about 0.5 in efficiency so they're almost at the same level i think i'd read that the absolute limit of efficiency for silicon based solar cells is about 30 i think so do you know if it's the same for perovskites jennifer or is the theoretical maximum higher i'm not actually sure but i know that that kind of maximum can be surpassed if we use tandem
or multi-junction solar cells where we combine um several photon absorbers and then for that i know that the efficiency is around uh probably around 40 maybe about that even so it's wow yeah but this isn't a lab like really straight to research lab conditions so it might differ in more let's say production environments yeah of course so silicon is used pretty extensively perovskites are catching up to silicon now they can get the same levels of efficiency so will
we start seeing perovskites in the solar cells that we see around us well there's still a way to a bit of a way to go because uh there are still some struggles with the stability i mentioned the first set of so perovskite solar cells that were produced in 2009 these first set of perovskite solar cells only lasted a couple of minutes before they started to degrade but now they can last for a thousand hours a few cycles there are still some things that need to be
improved in terms of stability before they can go become more popular commercially yeah i guess that would be a huge issue for you laura if you put your solar panels on your house and every you know weekly having to change them i wouldn't want to be climbing up onto the roof every single week to change solar cells there's so many things that we have to take into consideration when you know making this technology going forward i also just want to add as a side from my very limited
experience of solar cells i did some research a while ago on tungsten fuzz which is this kind of nanostructure that forms inside fusion reactors it turns the tungsten black and so it has this potential for photovoltaic applications which i thought was very exciting so it like something that might be bad in one field can be good in another which i think is really important to remember scientists because sometimes we get really disappointed with our results or we
see something that's not ideal for our application but we should also try and think of those other applications that may find it useful that was a bit of a bit of a tangent so going back to the the solar cells so we've discussed a bit about the two potential types of solar cell materials so we've got uh silicon and we've got perovskites could you tell us kind of a bit more about the specific material properties like what what are they maybe we can start with perovskites yeah perovskites has
a molecular structure of the type abx3 i don't know what that means it sounds like a cake pop a k-pop exactly no so it's basically an organic inorganic metal halide compound so it's got a lot of different compounds in there like i said it's got a structure type called abx-3 so group a is an organic cation so like methylamonium or formidinium group b is normally a metal cation which can be a lead or tin lead is one of the more popular ones and then group x is
normally a halogen uh halogen on ion so chloride bromide or iodide or a mixture of these halogens yeah so as you heard they often use metal cat or lead as the metal cation and as you know there's some toxicity associated with lead so lead-free options are also being explored very cool and laura what about the silicon ones how are they made so you start off with some some really pure silicon and then you dope it with either something that will lead to sort of i guess
like a deficit in electrons when they bond to each other or um an excess of electrons i think so you generate something called a p n junction um so you have these two slightly different compositions of silicon semiconductor so they can be a semiconductor i should say so the p type might have boron in it which makes it deficient in electrons so it's overall like positive charge and the n-type commonly uses phosphorus in there which generates a net negative charge i think
that's how i understand it anyway makes sense to me p positive and negative it's a semiconductor i mentioned that band gap of 1.1 electron volts so when the sunlight hits it electrons are liberated and they can flow from that negative to positive type of semiconductor and you get this charge that moves i think the voltage is dominated by that band gap so even if you shine more intense light on your solar cell you won't generate more voltage you might produce more current
though so you might have more electrons flowing but you can't change that voltage so that's what i read about how they work and how their composition affects how they work so doping with the board and the phosphate makes it easier to generate that current very cool so but it seems like there's in both cases there's some pretty crazy materials involved in in both of them so we've got the lead for the perovskites and then boron and was it uh what's the lithium um
i mentioned phosphorus for the other phosphorus sorry menstrual phosphorus yeah uh boron and phosphorus for the for the silicon one so it seems it's quite complex can i just ask because it's quite interesting that you said you have like you have n-type and p-type uh silicon uh solar cells do you combine the two layers yeah so you kind of sandwich them together and they'll be this sort of i think it's called like a deficit region in the middle where you've got
something strange that i'm like don't really get my head around happens where the electrons flow yeah and yeah it's that difference i guess like the potential difference in the p-type and the n-type that helps generate that current you generate it even if you didn't have the different types it'd just be less efficient i think that's quite it's a bit different in uh perovskites because it's like an ambipolar type of material
so when it absorbs when the perosquid absorbs a photon it forms holes and electrons and then the electrons are kind of separated they transport to this electron transporting layer or titanium oxide and then go to the anode which is normally type of conducting glass and then the holes go through like a hole transporting layer and then through to the cathode which is often a metal made of gold or silver so typically a perovskite device have five different layers with the perovskite sandwiched
in the middle okay so when i was looking into it i got the impression there might be more to it in the silicon based ones but i didn't know if they were doing what you mentioned multi-junction cells before yeah if there was some sort of multi-junction thing or they were just over complicating it yeah because obviously you still need some like some layer that will stop the electrons from just going wherever the hell they want yeah yeah but
yeah it does sound like the perovskites operate in a slightly different way yeah my mind is just blown by how complicated both of the technologies if someone is not an expert it's it's crazy that something as simple as harnessing the power of the sun but the the technology behind it is it's just mind-blowing well you tried to make a spider-man record and go back to talking about fusion maybe yeah it's just serving i have to bring it back to fusion every time of course but yeah let's talk
about climate change because that's what solar cells are meant to be one of the tools that we're using in order to combat climate change and move us away from using fossil fuels and other things that means they should be sustainable right so the cells should be sustainable if we're using them to combat climate change but what do we really mean by sustainability and are they actually sustainable we kind of talked about this in our what do you mean by zero waste episode
a few months ago with uh antonia and cara who were sort of experts in this sort of thing we talked about it then in terms of you obviously want to gather your raw materials in a way that does the least amount of harm or even makes a place better than it was before and then once you've used your product you need to dispose of it responsibly or reuse it or recycle it in some way you don't want to just send it to landfill i don't really know much about where the raw materials come from
other than silicon is quite prominent in the world but i do know that uk legislation means you can't just throw them away you have to recycle them somehow and any solar panel made within the last i think it's 15 years the producer has to take it back from you and use it responsibly and i found wildly conflicting stories about how recyclable solar panels are or how reusable they are as well and they've got a design life of about 30-ish years they gradually produce less electricity
as they age even though the conditions could be exactly the same so you could stick your solar cell in a lab for 30 years and completely control the conditions and it will still produce less electricity over time just because materials change they break down eventually but you can't recharge them for example and use them again after 30 years ah yeah there are things like cracks develop and things like that some of the problems that i read about didn't relate to
the silicon material itself it was things like electrical contacts break or the glass that covers it that could shatter or i think there's some sort of plastic covering as well that can turn brown because of sunlight so lots of ways they can break that don't seem to have a lot to do with the silicon which i was slightly surprised at in a way because i always considered that because that silicon is a crystalline material and you're bombarding it with photons and you've got
electrons flying around that eventually bonds will break and defects will develop in that structure which does affect their efficiency but it's not the most common way that silicon solar cells fail apparently um so you could refurbish them i guess you could replace the glass or fix the electrical contact and for the perovskites is that the same thing or is it more as you said before jennifer about the stability so it's actually the perovskites themselves that degrade over time
uh yeah i think it's more related to the perovskite itself i'm also thinking about the fabrication and so the energy that needs to be put in to actually fabricate the solar cell and then also the recycling bit like how easy it is to recycle all the parts of the solar cell in the end and for the recycling bit i came across this uh interesting research paper that described how this can be done in further detail and how the cell can be disposed in a safe
manner and it seems like you're able to remove each layer because like i said before typically a perovskite solar cell would contain five different layers and you're able you if you are able to separate each of them and take them out for further processing and then some of these layers can be reused later on like the lead-containing perovskite can be recycled and we use to make more peroxides or something else and the most expensive part of the solar cell is actually
the conductive glass that can also be reused for other purposes or for new perovski solar cells another aspect of sustainability is obviously the uh the lifetime of the these solar cells and i think as long as we have these uh stability issues this is gonna be a huge uh obstacle in actually i don't know reaching these sustainability goals or even commercial goals so you're saying perovskites don't last anywhere near as long as silicon-based solar cells so i can imagine at the
minute most of the energy would go into producing the solar cell so it takes more energy to produce the perovskite solar cell than the perovskite solar cell will produce over its useful life yeah and you need to get that balance right yes although i wouldn't say it's i mean they still last long but probably not nearly as long as silicon-based solar cells that's yeah that's my take but i think initially when it comes to the the amount of energy that's put into
single crystalline silicon that's much higher than for example fabricating perovskites because it's just a solution based process where you use spin coatings and you anneal the solution so that to settle the perovskite film and the annealing process is done in quite low temperatures so below 100 degrees but i think for silicon it's much higher than that right yeah because you want to get the silicon really pure to begin with and then you it sounds like you go through a whole range of
steps and it depends on exactly which manufacturer is what some of them use particle accelerate is to dope the silicon which i think sounds like wildly inefficient because particle accelerators tend to consume a lot of electricity yeah so we've kind of covered some key areas of sustainability there in terms of you know the amount of energy it requires actually to manufacture these solar cells i guess another key area of sustainable is do they produce enough electricity
for us to be able to use them and i guess that depends where they're located maybe it's better if they're somewhere sunny unlike manchester which is quite quite great a lot of the time funnily enough i was just reading an article about how dubai is a really inappropriate place for solar panels because it gets it's too hot and they get less efficient at higher temperatures and there's a lot of a lot of dust as well so you cover your solar cell in dust and you the photons
can't come in but the panel gets really hot and it becomes less efficient anyway and apparently dubai is just not the place to do it even though it could be really sunny that's crazy i'd never have thought that i'd be like that's the ideal place to put solar panels so there needs to be like a kind of compromise in terms of climate conditions so in that case is it better to have the solar sun solar sun solar panels all in one place with the optimum conditions and then somehow transport the
electricity we produce yeah this is what i wonder see if they work better at colder temperatures are you better having them closer towards the poles of the earth where you obviously get sunlight for like what six months of the year at one pole and then the other six months of the at the other pole and it's really cold right so they should be really efficient and then you just kind of oscillate between the two so you've got a constant supply of electricity
i don't know maybe that's a really stupid idea makes sense in my head though that's a very clever idea i think i like that we just need a way to figure out how to transport the electricity we would produce right which i guess is more of a i feel there is technology to transport electricity we do that every day but it's very government specific so i guess that requires political cooperation if we want to share electricity between many different countries yeah rather than
rather than a science yeah i go for the science and everyone else all the engineers say no you can't do that because of something else that's what happened last week in our previous episode in some countries the power grid system isn't as extensive so it's down to more down to every individual to make that supply themselves with energy so in this case you would have more of a decentralized energy supply system where people would maybe in this case it would be
better to you know have your own so yeah exactly yeah see in a way i prefer that idea because i have no idea exactly where my electricity comes from at the minute and i don't really know what goes into making electricity get from where it is to where i am but if there was a community of photovoltaics engineers and electrical engineers near me and i could see the solar panels and i could talk to the people that ran them i'd understand it better and i think i feel
a little bit more comfortable about using these things and not just taking them for granted yeah i agree with but like you appreciate things more and i guess it's more accessible i feel smaller things are always more accessible to people like if you have your own supply then you control control that basically that's yours to do and more people can use it for example people who grow heroin heroin
farmers in afghanistan have made good use of solar technology there was a really interesting article that we read so that's one example of people taking control of their electricity production not too sure the production of heroin is the best use there not necessarily the best but interesting nonetheless but i also think one of the things that we've covered is that it's really complex technology so that's another thing that makes me think is it easy for people to maintain them if
it breaks do you then need specific engineers to come in or is it something you could fix yourself if there were any problems just because of the complex technology that's involved yeah so again having some local engineers that know how these things work i think could be more useful than just like sending it out to someone and saying there you go there's an electricity supply you have to figure out how it works though yeah is there any other simpler technology that we could use instead
of solar panels to harness the sun um there are like solar collection systems aren't there i mean the way photovoltaics are going is they're getting more and more complicated they can try and make them more efficient when jennifer mentioned those multi-junction cells that's effectively putting more and more layers of more complicated things that are made from different chemical elements that were used by different parts of the energy spectrum of the light that comes from the sun
um or will will split the photon so yeah we seem to be going more complicated but i didn't really didn't really come across much that was simpler in terms of solar so yeah there are the solar stoves that i've seen uh in afghanistan but it's like a giant mirror basically which well lots of little mirrors i think and then they focus the light in the center so people can use that for cooking and like for heating stuff pretty effectively without any emissions
so that's a really i found that really nice simple kind of technology but yeah i think if we want to produce electricity the technology does seem to be kind of becoming more more and more complicated yeah it would be nice if things went simpler because it it means you can you're more likely to be able to maintain it which again gives you that sense of i can use this thing and be a bit more self-sufficient rather than relying on the electrical engineers to come and fix my solar cell
or replace the glass on it because it's cracked because of temperature differences or something yeah and i think that's for all technologies right a lot of stuff now we can't see how it works yeah i find that really bad like you know if your phone breaks you can't open it if your laptop breaks you have to take it they will fix it you can't fix it well certain brands other brands are still better for laptops but apple especially is really bad um yeah for this i feel another use of silicon
there we go but um not solar panels but yeah it's definitely something to think about yeah i was just looking up as we were talking you're asking about where's better could you do it somewhere it's really sunny um apparently the average installation in the uk can generate something like 3 000 kilowatt hours per year but the average consumption is less than that per household depending on the size of your house of course so in theory it would be possible to
generate all of your own electricity and that's in like standard uk weather so not being incredibly sunny and not being incredibly hot or incredibly cold presumably that's great so everyone should be getting solar panels on their houses yeah everyone in the uk anyway but dubai you've still got a problem which i really would have thought at the beginning of this episode it would have been the other way around did you know that the largest the concentrated solar power
plant project is in morocco it's called the noor power plant that's very cool and nor means light oh ah cool i knew none of these things that's pretty cool that they're making a whole power plant out of solar cells actually i've never heard of that so is it currently sort of connected to the national electricity grid in supplying people's homes do you know no i'm not sure it looks like it's placed in the desert somewhere uh i mean how dusty it is is
it like too mine they have to clean it yeah i don't know but it looks like it's gonna cover an area of 2 500 hectares whoa that's massive oh yeah no it will supply electricity to their grid that's pretty impressive yeah that's awesome it sounds like that's a good place to come to an end of the episode i've definitely learned a lot i think we've discussed the two main candidates the solar panels the one that's currently used is the the silicon solar panels but perovskites are this
really cool new technology that are accelerating uh incredible speed in less than 20 years they've almost got the same efficiency as silicon now and it's more of a developing the longevity of the panels to make sure they're stable we've discussed kind of what sustainability really means and considered the different parts of manufacturing process how we get the electricity where's the best place to put the solar panels apparently the uk is not bad who'd have thought
it so that's our take on solar cells find us on twitter if you want to carry on this conversation or leave a comment on the episode and see you next time the views expressed in this podcast belong entirely to the person that said them they do not represent any industry or organization if you enjoyed listening to these views it would really help us out if you could rate us leave a review and tell a friend this podcast was sponsored by no one but if you're interested in
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