Information Video about Perovskite Solar Cells

In the video below, a new technology how to build solar cells will be explained in detail.

Here some basic explanation:

Perovskite solar cell

A perovskite solar cell (PSC) is a type of solar cell which includes a perovskite-structured compound, most commonly a hybrid organic-inorganic lead or tin halide-based material, as the light-harvesting active layer.[1][2] Perovskite materials, such as methylammonium lead halides and all-inorganic cesium lead halide, are cheap to produce and simple to manufacture.

Solar cell efficiencies of laboratory-scale devices using these materials have increased from 3.8% in 2009[3] to 25.7% in 2021 in single-junction architectures,[4][5] and, in silicon-based tandem cells, to 29.8%,[4][6] exceeding the maximum efficiency achieved in single-junction silicon solar cells. Perovskite solar cells have therefore been the fastest-advancing solar technology as of 2016.[1] With the potential of achieving even higher efficiencies and very low production costs, perovskite solar cells have become commercially attractive. Core problems and research subjects include their short- and long-term stability.[7]

Source: Perovskite solar cell, (last visited May 12, 2022).

Video transcript:

0:00 In this video we’ll explore the world’s  fastest improving new solar technology,  

0:04 and provide an exclusive peek inside the lab of  a team working on this breakthrough material.

0:10 Right now, while you’re watching this video, a  giant fusion reactor 93 million miles away is  

0:14 irradiating the earth with about as much energy  as all of human civilization uses in a year.

0:19 So why aren’t we harnessing this abundant,  

0:21 renewable energy source to meet  all of humanity’s energy needs?

0:24 It’s not an issue of physical impossibility,  “If you wanted to power the entire U.S.  

0:28 with solar panels, it would take a fairly  small corner of Nevada or Texas or Utah.  

0:32 You only need about 100 miles by 100 miles of  solar panels to power the entire United States”

0:37 Currently, only 2% of global electricity  comes from solar power. And 90% of that,  

0:42 comes from crystalline silicon-based solar  panels, the dominant material technology.

0:47 While abundant, silicon has  downsides related to efficiency,  

0:50 manufacturing complexity, and pollution that  prevent it from being an absolute no brainer.

0:57 Now what if I told you about  a material that was lighter,  

1:00 more efficient, and simpler  to produce at a lower cost?

1:03 An inexpensive solution that can  make a photovoltaic cell so thin,  

1:06 that just half a cup of liquid would be enough  to power a house? A solar panel so lightweight,  

1:11 that it can be balanced atop a soap bubble.

1:13 Well, that folks, is known as the holy  grail of solar, They’re called Perovskites,  

1:18 and they might just revolutionize how  humans generate energy from sunlight .

1:21 We headed to silicon valley to meet  Joel Jean, the CEO of Swift Solar,  

1:25 one of the leading teams working to bring  Perovskite solar technology to light.

1:34 It’s a new kind of thin film technology. So you’ve  probably heard of that for a long time, different  

1:40 kinds of thin films have come and gone over the  years. What we do here is a new kind of material.  

1:44 It’s called perovskites, a new semiconductor  material that absorbs light really effectively,  

1:48 also transports charge. So it just turns out  to be very efficient material for solar cells.

1:53 Solar cell technologies can be classified into  two categories, wafer-based or thin-film cells.

1:58 Wafer-based cells are fabricated  on semiconducting wafers,  

2:01 and are usually protected by a material  like glass. These are the crystalline  

2:04 silicon cells you’ll typically find  on bulky roof mounted solar panels.

2:08 Thin-film cells are made by depositing thin layers  of semiconducting films onto a glass, plastic,  

2:13 or metal substrate, and use 10 to 1000 times  less material than crystalline silicon cells.  

2:18 These thin-film cells are light and flexible,  but have lower average efficiencies.

2:22 You can make thin film cells from  amorphous silicon, or more complex  

2:25 materials like Cadmium Telluride, but  scientists have been on the hunt for  

2:29 better thin-film solar technologies  that can see more widespread use.

2:32 These materials are known as “emerging thin films”

2:36 Currently, Perovskites are the leading contender.

2:39 What could you do with a  solar panel with 100 times  

2:41 the power-to-weight performance  of conventional silicon panels?

2:44 A solar material so abundant, it  could be painted on skyscrapers.

2:48 Flexible, lightweight, highly  efficient cells could open up a wide  

2:51 range of applications where traditional  silicon cells are too heavy and rigid.

2:55 But before we cover your Tesla  model S plaid in perovskite solar,  

2:59 what exactly is this revolutionary crystal?

3:02 The Perovskite crystal structure was  first discovered as the naturally  

3:05 occurring mineral calcium titanium oxide.

3:08 But the Perovskites used in solar cells  don’t need to be mined from the earth.

3:11 A perovskite is any material with a crystal  structure following the formula ABX3.  

3:16 Where ‘A’ and ‘B’ are two positively  charged ions, often of different sizes,  

3:20 and X is a negatively charged ion.  

3:22 Scientists realized that they could create a  diverse range of man made perovskite crystals,  

3:27 following this same arrangement,  that have very useful properties.

3:30 So we use basic, you know, metal halide salts,  so things like lead iodide or some some organic  

3:38 salts as well. And we combine them  to make these inorganic organic,  

3:43 hybrid perovskites. So if you can form  them in solution, you can form them out of,  

3:48 in vacuum out of vapor phase. And they condense  into forming these perovskite crystals.  

3:53 And the thin films, they’re like  multi-crystalline, which means that  

3:56 there’s a bunch of little crystal domains, they  turn out just to be really good semiconductors.

4:01 So just how efficient are perovskite solar cells?

4:05 The most efficient modern silicon solar panels  you’d find on a home only work at best around 20%  

4:10 efficiency, but the theoretical conversion  efficiency of single junction solar technologies  

4:15 is about 33%, called the Shockley-Queisser limit.

4:18 That’s the fundamental limit  for a single solar cell singles  

4:22 material based solar cell. Perovskites  are the exact same thing. Silicon,  

4:25 perovskites, cadmium telluride, CIGS, all  of these technologies have the same limit.

4:29 But perovskite solar cells can be made  in a form factor that’s capable of  

4:33 much higher efficiency limits, pushing the  boundaries of possibility for solar power.

4:37 To understand why perovskites hold an  advantage over traditional silicon solar cells,  

4:41 let’s first do a basic refresh of how photovoltaic  cells convert sunlight to electricity.

4:47 The top and bottom parts of a  solar cell contain semiconductor  

4:50 materials with different electrical properties.

4:52 In a traditional silicon cell for example,  silicon is used for both layers, but each layer is  

4:57 modified or “doped” with tiny amounts of different  elements to create different electrical charges.

5:01 The portion that contains a higher concentration  of free negatively-charged electrons is called  

5:05 the n-type region, and the side that  contains more positively charged holes,  

5:09 or missing electrons, is  known as the p-type region.

5:12 The boundary between these two layers is known  as the p-n junction. When an n-type and a p-type  

5:16 material are put in contact, free electrons from  the n-type material and free holes from the p-type  

5:21 material move across the boundary and cancel  each other out. The electrons fill in the holes.  

5:26 This uncovers the fixed positive and negative  charges of the dopant ions, which creates a  

5:30 built-in electric field that stops more electrons  and holes from moving across the boundary. This  

5:35 electric field corresponds to a built-in voltage  and acts like a one-way valve for charge carriers.

5:40 The fundamental unit of light is  the photon, which represents the  

5:43 smallest packet of electromagnetic  radiation of a given wavelength.

5:47 When a photon from sunlight hits  a solar cell and gets absorbed,  

5:50 it creates an extra free electron and hole,  which are separated by the electric field  

5:54 and pulled to opposite sides of the  cell. This creates a photocurrent.

5:58 If electrodes are attached  to both sides of the cell,  

6:00 forming an electrical circuit, an electric  current will flow as long as the sun is shining.

6:06 The magic of perovskite crystals  lies in their customizability.

6:10 Single junction solar cells can only  absorb a portion of the solar spectrum  

6:13 depending on what semiconductor material they use.

6:15 The lowest energy of light that can be absorbed  in a semiconductor is called its band gap.

6:20 A semiconductor will not absorb photons  of energy less than the band gap;  

6:23 and the useful energy that can be extracted from  a photon is no more than the band gap energy.

6:28 This means much of the energy in sunlight goes to  waste when it hits a single junction solar cell,  

6:32 but because the band gap of perovskites can be  easily changed, you can stack perovskite layers  

6:37 on top of each other that are chemically tuned  to absorb different parts of the solar spectrum.

6:41 This results in a solar cell with multiple  p-n junctions that can produce electricity  

6:45 from a broader range of light wavelengths  or extract more energy from each photon,  

6:49 improving the cell’s efficiency.

6:51 So when you stack two solar cells on top  of each other, that’s called a tandem,  

6:55 or a multi junction solar  cell. And when you do that,  

6:58 that actually pushes that efficiency limit  up from 30% to over 40, about 45 and 46%

7:04 Theoretically, an infinite  number of junctions would  

7:06 have a limiting efficiency of 86.8%  under highly concentrated sunlight.

7:11 and it goes higher with more layers, but  it also becomes more expensive and you get  

7:14 diminishing returns. So generally, we talked  about doing two layers or making a tandem,  

7:19 and that that’s kind of the the  real selling point of perovskites.

7:22 So perovskite tandems convert more of the  sun’s energy into electricity, rather than  

7:26 wasting it as excess heat. So what are the exact  efficiency percentages we’re talking about here?

7:32 we shouldn’t expect solar  cells above 40% efficiency,  

7:35 this kind of solar cell for a long, long time.  I think in theory, it could get there. But  

7:38 realistically I think in the 30’s is is  doable, which is still a substantial jump from,  

7:44 you know, what you see out  there on the market today

7:46 It’s not just performance that’s improved. The  

7:48 nature of Perovskites allow for  manufacturing advantages too.

7:51 So you only need less than 1% of this  material that you need for a silicon cell  

7:56 to absorb all the sunlight. So in theory, you  can save money, you can basically make this  

8:00 stuff a lot cheaper. The cool thing about the  perovskites is that they turn out even though  

8:05 it’s made of this kind of not perfect material,  you can actually make a very, very efficient solar  

8:09 cell. It’s formed at low temperatures. Silicon,  usually you have to crystallize that something  

8:13 like 1400 degrees Celsius, with perovskites, you  can form it at less than 100 degrees Celsius.  

8:19 So that means that you can actually use  smaller equipment, and you can kind of use  

8:23 more standard chemical processes. And you can  form the solar cells on things like plastics,  

8:28 so things that would melt under  high temperatures you can actually  

8:30 use to make solar cells on. So you can make  something really lightweight and flexible as well.

8:35 Perovskite Thin films can be made by synthesizing  a solar ink of sorts, and gently heating it until  

8:40 the perovskites crystallize, just like salt  crystals emerging from evaporating sea water.

8:45 Now let’s go deeper into the lab,  to take a rare and exclusive sneak  

8:48 peak behind the scenes to see how  Perovskite solar cells are made.

8:52 Yeah, so this guy is called a thermal evaporator.  So it’s, it’s one of many kinds of deposition  

8:57 tools that we use to, to put down thin films.  So when you look at a perovskite solar cell,  

9:02 it’s like any other thin film device like an  organic LED, or a cadmium telluride solar cell,  

9:07 it’s got a lot of thin film semiconductor  layers. And one of the ways you deposit some  

9:10 of those layers, is using techniques like thermal  evaporation, where you heat up a source material,  

9:15 maybe it’s silver, or maybe it’s a precursor  for one of your semiconductors. And you melt it,  

9:20 you evaporate it and then you have a cold  surface that you condense on. And that cold  

9:23 surface is actually just at room temperature.  It’s a plastic sheet or a glass sheet,  

9:27 or even a silicon wafer that  you’re trying to deposit a film on.

9:30 The substrate sits at the very top of the  chamber. It’s under high vacuum and you again  

9:34 evaporate this material and it condenses  and forms this uniform thin film and you  

9:38 do that many many times with different kinds of  techniques. And that gets you your solar cell.

9:42 You can also make perovskite cells  with spin-coating, screen printing,  

9:46 electrodeposition or even printing the material  on a sheet just like an inkjet printer.

9:52 Here is the end result, a small  rectangular perovskite solar cell.

9:55 So this is the side that’s facing the sun,  correct, and this is the back of the cell?

10:00 Yeah, the side facing the sun is actually you’re  looking through the glass. And on the other side  

10:05 of that glass, there’s a perovskite layer, kind of  sandwiched between the contacts. So the contacts  

10:11 are, what pull the charge out of the perovskite.  So there’s a transparent conductor on that on the  

10:16 close the side closest to us. Then there’s  the perovskite. And then on the other side,  

10:21 if you look at it from you know, from the  backside, there’s these silver electrodes.  

10:25 It can be any different kinds of metals. But that  side doesn’t have to be transparent because you  

10:29 actually want the light to reflect back  into the semiconductor not go through.

10:33 These solar cells are just lab samples  designed to test different perovskite formulas.

10:38 And you can see that these different pads,  each of these squares is a solar cell.  

10:43 So we have six different solar cells on one  substrate for for r&d purposes, for testing.

10:48 Swift solar is trying to create a perovskite solar  

10:51 cell with the perfect mix of longevity and  efficiency ready for commercialization.

10:55 So how do you test the cells if it’s a  cloudy day? The sun can be quite unreliable,  

10:59 even in California.

11:00 We actually use this, this machine right here. So  this is a it’s a, it’s called a solar simulator.  

11:04 So it’s actually just a fake sun. It’s it’s an LED  array that basically has all the colors basically,  

11:11 it has a lot of different colors  of LEDs something like 20 Different  

11:14 LED colors in an array with optics to make it  really uniform. So the idea is here we don’t want  

11:19 to have to take our solar cells outdoors and test  you know if it’s raining we can’t test our cells.

11:24 what are these here. Are these the  circuit boards that the solar panels,  

11:27 that measure the voltage and the  solar panel sit on top of them?

11:29 Yeah, measure the voltage and current. So this  is you can kind of see this, it’s the same shape  

11:33 and it’s got a bunch of pads on there. And each of  those like are basically leads to pull out current  

11:38 or measure. yeah, to measure voltage, so or apply  voltage. So you can see we can do 20 of these at  

11:43 once. And it basically automatically moves around  to test the cells, each of them individually.

11:50 Perovskites have improved greatly since scientists  first began testing them, and are now beginning  

11:55 to surpass mono and poly crystalline  silicon cells in conversion efficiency. 

11:59 As perovskites start coming into commercial  usage, where are we most likely to see them first?

12:04 All the traditional solar applications. On  your rooftop, out in the field somewhere,  

12:07 in the desert, on commercial rooftops, on  residential rooftops, like those are all fair game  

12:11 down the line. Perovskites aren’t ready for that  kind of, you know, primetime yet, the stability is  

12:17 still challenged, like you’re getting them to last  for 25 years, we can’t No one can say that yet,  

12:21 confidently, we don’t have the field data to  prove that. So there’s a lot of engineering  

12:25 work and science to be done to get to that point.  But there’s a lot of applications where you don’t  

12:30 need 25 year life, right, like a car maybe only  needs 10 or 15 years. There’s things like high  

12:34 altitude drones, right, which are going to be  fully powered by solar, you know, they’re flying  

12:38 the stratosphere at 65,000 feet beaming down  internet. So that kind of thing is needs very,  

12:43 very lightweight solar needs very efficient solar,  it doesn’t need to a 25 year life, you maybe only  

12:47 need a couple years, five years. So that kind of  thing you can imagine being powered by perovskites  

12:53 very soon, same with solar wristwatches or  small IoT Internet of Things, devices. A lot  

12:59 of these kinds of mobile applications where you  can imagine perovskites kind of coming into the  

13:03 market and then eventually improving towards the  rooftop, towards the utility scale applications.

13:09 So what exactly are the challenges  that are preventing perovskites  

13:12 from dominating the solar energy  landscape, and changing everything?

13:16 we’ve spent a lot of time in this lab actually  working on the challenges of developing this  

13:20 technology to a point where it’s ready for, for  production and for scale up. There’s things like  

13:25 stability, which is probably the core problem  for perovskites is, how do you make these cells  

13:30 last effectively, for years in the field, under  high temperatures, a car roof might get up to 80  

13:35 degrees Celsius, right or more on a hot day.  So you need to be able to like survive those  

13:39 temperatures for years at a time. And I think we  tried to do we do a lot of tests to and iteration  

13:43 on the materials on the device stack, the stack  of materials we use on the design of the device  

13:48 itself on the packaging, to make sure that  we can survive those kinds of temperatures,  

13:53 high humidities, the different kinds  of environments you face outdoors.

13:57 The relative fragility of the perovskite material  requires protection to shield this semiconductor  

14:02 layer from environmental stresses and degradation.

14:04 The international standards for terrestrial solar  

14:06 panels require harsh testing that  simulates 25 years of being outside.  

14:10 In these tests panels are heated up and  even battered with simulated hailstones.

14:15 The problem with perovskites is that they’re  still relatively new. We can subject them to these  

14:19 harsh simulated tests that give us a pretty good  idea of their longevity, but we just don’t have  

14:23 the real world data yet like we do for silicon  panels, which have been in use for decades now.

14:28 While perovskites are still in the research &  development phase of the technology life cycle,  

14:33 there are many teams all over the world working on  

14:35 improving their efficiency and stability  to bring them into commercial adoption.

14:39 The raw materials for perovskites  are abundant around the world,  

14:42 and the solar cells can be made using  relatively simple manufacturing processes.  

14:46 This means that Perovskites can rapidly scale when  they’re ready for mass market commercialization.

14:51 It’s estimated that Perovskite panels  could cost up to 15 times less per  

14:54 watt than modern commercial silicon solar panels.

14:57 In addition, engineered perovskite materials  absorb all parts of the solar spectrum  

15:01 efficiently to produce the highest possible  power output and Ultra-thin films open the  

15:05 door to new product formats with unprecedented  power-to-weight ratios and high flexibility.

15:12 A future with cheap, abundant solar power  could open the door for a variety of use  

15:16 cases where current photovoltaic  technology does not yet make sense.

15:20 How about these electric yachts I’ve filmed for  previous Electric Future videos. Their range could  

15:24 be radically improved with higher efficiency,  lightweight, integrated perovskite solar panels.

15:29 We could see integrated Solar panels  on trucks, buses and cars and any other  

15:32 applications where sunlight is not yet considered  energy-dense enough to provide meaningful power.

15:37 Imagine buildings covered in transparent  

15:39 photovoltaic glass windows  that generate electricity.

15:44 It’s difficult to predict the future of solar.  While perovskites are promising, serious  

15:48 researchers avoid playing favorites. Instead,  they view all technologies objectively based on  

15:53 increased efficiency, reduced materials usage,  and reduced manufacturing complexity and cost.

15:59 Solar photovoltaics are the fastest-growing  energy technology in the world today and a leading  

16:04 candidate for terawatt-scale, carbon-free  electricity generation in our lifetime.  

16:08 If you’d like to better understand some of  the concepts we presented in this video,  

16:11 it’s important to first learn  the fundamentals of solar energy. 

16:14 Brilliant does a great job of taking  complicated science and breaking it  

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16:25 and develop your intuition so you can truly  understand these breakthrough technologies. 

16:29 I’ve taken brilliant courses on  electricity & magnetism and solar  

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