Perovskite Solar Cells: Game changer?

in july 2017 at the u.s national governors association meeting elon musk told more than 30 state governors exactly how much land would be needed to power the entire country with solar energy it's if you only need about 100 miles by 100 miles of solar panels it's proud of the entire united states and then the the batteries you need to store that energy to make sure you have 24 7 power is one mile by one mile one one square mile that's that's it he was speaking a bit hypothetically of course we all know the world isn't as simple as that and the barriers to achieving that goal even if it were set as a target would be pretty mind-boggling not least of which would be the storage interconnections to an old and failing grid and of course the fierce and brutal opposition that any such proposal would face from the fossil fuel industry but there's another potential hurdle that isn't quite so well understood and that's the fact that by the very nature of the way existing solar panels are constructed there's a physical limit to how much sunlight they can convert into electricity that limit equates to about 30 efficiency and in fact the most common solar panels used today actually only achieve a real-world efficiency of about 23 and even that took about 40 years to achieve the panel's dear old jimmy carter had installed on the roof of the white house back in 1979 were barely more than 14 efficient unsurprisingly then there's a huge global competition to discover and develop new and exciting ways to improve solar panel efficiency in an economically viable way and one of the most promising new materials in development is something called perovskite so what is perovskite and how will it help hello and welcome to just ever think i mentioned that it was a new material but actually perovskite was first discovered in the ural mountains in the early 19th century by a geologist called lev perovsky perovskite in the wild is a mineral made from calcium titanium and oxygen rather than traipsing around the world digging up the naturally occurring mineral though scientists have developed a whole class of materials called perovskite structures they have the same crystalline cube and diamond-like shape as naturally occur in perovskite but they can be synthesized from a fairly wide variety of commonly available and relatively cheap chemicals the scientists refer to them as abx-3 structures with a and b acting as cations and x acting as an anion so how can perovskite structures help with solar panel efficiency well let's start with a quick look at how existing solar panels work the active part of a solar cell is a wafer made of a semiconductor material typically silicon semiconductors like silicon don't normally conduct electricity well but they can be made more conductive under certain conditions the cell has three layers the top silicon layer contains a tiny amount of an element like phosphorus that has more electrons than silicon and that gives the top layer an excess of electrons that are free to move around which makes the silicon more electrically conductive this process of adding a second element to the lattice structure of silicon is what the scientists refer to as doping the top layer likes to collect electrons and because electrons have a negative charge the layer is referred to as the negative type or n-type layer when sunlight hits the solar cell the very short ultraviolet waves don't penetrate the surface at all and the very long infrared wavelengths either bounce off or actually pass right through the cell without interacting with anything but the wavelengths that contain visible light are absorbed into the middle layer of the cell where a photon of light can knock an electron off an atom of silicon and that produces a free negatively charged electron and a corresponding hole where the electron came from and scientists refer to this hole as an effective positive charge because the top layer likes to collect electrons the freed up electrons jump up into that layer the bottom layer is another silicon lattice this time doped with a different element typically boron boron has fewer electrons than silicon the bottom layer likes to collect the effective positive charge left behind by the missing electrons in the middle layer so the bottom layer is referred to as the positive type or p type layer and the positive charge jumps down here stay with me here folks there's more the metal lines you see on solar cells are typically made of extremely thin strips of silver that are printed on top of the n-type layer the bottom p-type layer sits on an aluminium plate unless you live in america in which case they sit on an aluminum plate which of course is not correct nevertheless if you connect wires to the top and bottom of the cell and run them through a battery or a device like a light then you've created an electrical circuit that'll keep flowing as long as sunlight keeps hitting the panel the efficiency of a silicon solar cell drops off a lot if there are defects or blemishes in the material so the cells have to be subjected to extremely high temperatures to get the defects out and of course that's very energy hungry and expensive and for reasons that are a bit outside the scope of this video the photons hitting the electrons in the middle silicon layer need a bit of extra help from things called phonons to provide enough energy to free the electrons and help them jump up to the top conductive layer getting randomly hit by a photon and a phonon is much less likely than just getting hit by one or the other on its own so to increase the chances of that happening the middle layer has to be made relatively thick which again adds significantly to the cost of manufacture back in 1961 two very smart boffins called william shockley and hans joachim quasa did some clever physics stuff to establish that silicon has a band gap of 1.1 electron volts and they calculated that this physically limited the amount of sunlight that a silicon cell could convert to electricity to an absolute maximum of about 32 percent that's now known as the shockley quasar limit and it's a fundamental function of all photovoltaic cells containing a single p-type layer and a single n-type layer which is sometimes referred to as a single junction cell the best modern commercial silicon solar cells are about 24 efficient with losses coming from a bit of light reflection off the front of the cell and a bit of light blockage from the silver wires on the cell surface so perovskites then well for a start off unlike silicon solar cells perovskites don't need that extra phonon to liberate the electrons from their middle layer which means they can be manufactured as very thin films using a technique known as solutions processing perovskite structures are also much more tolerant to defects than silicon and that eliminates the need for the high cost high energy machinery that silicon cell production requires it also means about 20 times less material is needed for each cell which in turn means a smaller environmental footprint from production perovskite cells don't use rare earths or any supply limited materials and they can be made into traditional rigid solar panels or flexible panels for more diverse markets like the leisure industry and return on investment can be measured in months rather than years one fly in the ointment is that the currently favored metal for the central part of the abx-3 perovskite lattice is lead which of course is a very heavy toxic metal substance so obviously not ideal on the face of it but as this article from solar panel world points out the amount of lead used is minuscule on average about 2 milligrams per watt for comparison a common automobile battery contains 20 pounds or 9 million milligrams of lead on average largely as a result of the automotive industry the lead recycling stream is already the largest and most complete of any material in the world even at a recycling rate based on one terawatt's worth of panels perovskite solar cell recycling would still only represent one tenth of one percent of all lead recycled globally and alternatives like tin are already being actively developed for use in perovskite structures there have been other operational obstacles to overcome though scientists have been experimenting with all sorts of combinations of materials in the crystalline abx-3 structure to improve stability and minimize degradation from the sunlight itself and from exposure to oxygen and moisture but again according to the findings of the solar power world report both light induced and environmental degradation parameters have exceeded 1 000 hour accelerated life cycle testing which is the photovoltaic industry standard for new technologies with some going as far as 10 000 hours researchers have been developing perovskite structures in laboratories for about a decade now and in that time they've increased cell efficiency from about two percent to around 25 today which is already better than the best commercially available silicon panels ultimately though perovskite cells are still constrained by that shockley quasar limit which is determined by the band gap but yet another advantage that perovskite has over silicon is that perovskite band gaps can be increased or decreased depending on the materials used in the abx-3 structure that brings in the possibility of creating multi-junction cells with different band gaps in each junction in a 2018 interview professor henry snaith of oxford university explained it like this the lighting so so if you have a very narrow band gap material this this would mean that it would absorb all the light over the solar spectrum you generate a very high current but you wouldn't generate very much voltage if you're very wide band gap semiconductor you can generate a lot of voltage but you're only absorbing a small fraction of the sunlight so if a semiconductor had a band gap of say three electron volts you'd only absorb the uv spec part of the spectrum and you want to absorb the uv the visible and the infrared so this leads to a compromise where a band gap for a single absorber material is the optimum band gap somewhere between one to one and a half electron volts and that gives you a maximum of somewhere around 30 to 32 efficiency but if you have multiple absorbers with different band gaps on top of each other you can significantly exceed the shockley quasar limit the simplest way is to put a perovskite cell on top of silicon silicon perovskite tandems have already reached 29.1 efficiency which is much higher than the 23 for a single junction perovskite cell and higher even than the all-time world record for crystalline silicon using a very advanced technology which is 26.7 but professor snaith reckons it doesn't stop at tandem cells he's confident that with a triple junction cell they can push towards 40 efficiency and that could be two perovskites on a silicon cell or an all perovskite combination so perovskites solar cells really do look like they offer the prize of an ultra adaptable ultra thin flexible cheap high performance solar cell which could accelerate the move away from fossil fuels and perhaps a bit closer to elon's 100 square mile analogy there are already several companies all over the world that are racing to capture this potentially enormous market including oxford pv a spin-off from oxford university co-founded by professor snaith himself i'll leave the last word though to the author of the solar world power article dave bouemi of prescient energy consulting who reminds us that to meet 20 percent of all global energy for the un's emissions reduction scenario the solar industry would need to install between 300 and 500 gigawatts annually over the next 30 years current global pv module manufacturing at 100 gigawatts per year already presents an enormous supply chain challenge perovskite solar with its unique simplified manufacturing attributes raw material performance and small environmental footprint makes it highly scalable quickly depending on the business model perovskite modules can be manufactured in facilities that cost fifty percent less than other solar factories and use less material the supply chain to support manufacturing is also small allowing for factories to be sited close to end markets the perovskite solar cell industry is in a state where its lab developments already exceed prior solar panel commercialization launch points as with all these new technologies the challenge of course is how quickly the simplified manufacturing can scale up for a given production method to enter high volume production leave your thoughts in the comments section below but that's it for this week before i go though i just want to let you know about a podcast that i was invited to take part in recently with climate activist mark buckley mark is an advocate for the united nations sustainable development goals a member of the world economic forum expert network and an award-winning global food reformist he was also one of the very first people to be trained by al gore as part of the climate reality project the podcast was posted last tuesday the 4th of august 2020 on all social media and also on youtube hopefully all the links should be appearing across the screen now and of course i'll leave them as clickable links in the description box below this video it was a very enjoyable deep dive into climate change sustainable living and the socio-economic and political challenges we face in our world today so check it out if you can a big thank you as well to our supporters over at patreon who keep the channel going and keep it fully independent and a special shout out to the folks who've joined in the last couple of weeks with pledges of 10 or more a month they are richard hall hokai tong ras van t dr iso venesius zachary and matt rosser and of course a big thank you to everyone else who's joined since last time too you can also get involved in influencing the direction and content of the channel and chat with other like-minded climate and sustainable energy advocates by visiting www.patreon.com forward slash just ever think and you can support the channel absolutely for free by subscribing and hitting that like button so we get noticed by youtube's search algorithm and get the message to more and more people each week dead easy to do that of course just click down there somewhere or on that icon there and don't forget to hit the bell icon as well so you get notified of new content each week as always thanks very much for watching have a great week and remember to just have a think see you next week you

Channel: Just Have a Think

Views: 403,612

Rating: 4.9360108 out of 5

Keywords: perovskite, perovskite structures, solar power, solar energy, sustainable energy, renewable energy, solar panels, solar cells, Professor Henry Snaith, swift solar, oxford pv, heliatek

Id: TkFf8kRwOo8

Length: 14min 59sec (899 seconds)

Published: Sun Aug 09 2020

Reddit Comments

[u/Altiloquent]

Without watching the video...people have been asking this for like a decade now. Given the ridiculous number of research groups that have worked on perovskites without a viable commercialization path (afaik) I will remain skeptical.

[u/MoleculesandPhotons]

Rule #1 of news headlines

If it is a question, the answer is probably "No."