What is special about perovskite?

The fastest new solar technology is a breakthrough technology called perovskite. Did you know the sun is a giant fusion reactor that is 93 million miles away and is radiating enough energy in the time it takes you to read this article to provide the whole of civilisation enough energy for a year?

So the question remains. Why are we not using this renewable energy to meet our energy? 

One thing we do know, it is not impossible. Elon Must stated not too long ago that it would only take about 100 miles by 100 miles of solar panels to power the whole of the United States of America.

Today, only 2% of global electricity comes from solar power. 90% of that comes from crystalline silicon-based panels which are the dominant technology we use for making solar panels today.

Downside Of Silicon-Based Solar Panels

There are a few things/downsides to silicon-based solar panels that hold them back. These include manufacturing complexity and pollution which prevent it from progressing as it could.

But today, we are here to discuss an exciting new material that is easier to manufacture, lighter, more efficient and cheaper to produce. 

A material that can produce a photovoltaic cell so thin, it only takes only half a cup of liquid to power a home. That can produce solar panels that are so light that they can be balanced on top of a soap bubble.

We may be talking about the holly grail of solar technology, and they are called perovskites, an exciting leap that could revolutionise the way we gather our energy from sunlight in the future. One of the leading companies that are working to bring this tech to the market is called swift solar.

Can You Describe Perovskite?

Simply put, it is a new thin film technology, a more efficient semiconductor material which can absorb light very effectively. And transports charge, making it a very efficient material for solar technology moving forward.

What Are The Two Categories Of Solar Technology?

Solar cell technology falls into two main categories. One being wafer-based cells and the other thin film cells.

Wafer Based cells are fabricated on semiconducting wafers and protected by glass. These are the bulky crystalline and silicon solar cells that are common sites on rooftops today.

Thin Film Solar Cells are made by depositing very thin layers of semiconducting films onto a material such as glass or plastic. The thin film can use up to 1000 times less material compared to crystalline solar cells.

Typically, thin film cells are known to be less efficient but can bend and are flexible. These Thin-film cells can be manufactured using materials such as amorphous silicon or even mor3 complex materials such as cadmium telluride.

Scientists have for many years been looking for a better thin film technology that will make this category of solar more efficient and thus can be pushed out for widespread use.

In the category of emerging thin films, the main contender is perovskite.

Could you imagine a solar panel with 100 times the power-to-weight performance seen in the best solar panels today?

A material so thin and abundant that could be painted onto buildings to collect the sunlight. So flexible, lightweight and efficient, the wide range of applications is limitless, and the future seems a lot brighter.

What Is Perovskite – Is It A Crystal?

The perovskite crystal structure was first discovered as the naturally occurring mineral called calcium titanium oxide. But thankfully we don’t need to mine the earth to get the perovskite used in solar technology.

Any material with a crystal structure that follows the formula ABX3 is known as a perovskite. In this formula, A and B are two positively charged ions, often of different sizes, with X being a negatively charged ion.

Scientists now know they can make a wide array of man-made perovskite crystals in an arrangement that gives them the useful properties needed for highly efficient solar cells.

Metal halide salts, such as lead iodide, and organic salts are combined to make organic/inorganic hybrid perovskites. And if they can be formed in a liquid solution, they can be formed in a vacuum out of the vapour phase. Then when condensed, form into perovskite crystals full of little crystal domains, which are great semiconductors.

How Efficient Are Perovskite Solar Cells?

Today’s solar panels you find on rooftops only work at about 20 per cent efficiency. When it comes to solar technology, there’s a thing called the Shockley Queisser Limit which is the fundamental limit (33%) for a single solar cell. Perovskites are the same thing as a single material-based solar cell. This means Perovskites, silicon, cadmium telluride and CIGS are all bound to this limit.

But perovskite can be manufactured in a way that makes them push the boundaries and achieve much higher efficiency limits.

Why Perovskites Have The Advantage

First, we will look at how photovoltaic cells convert sunlight into electricity.

The top and bottom of a solar cell contain semiconductor materials with different electrical properties. The top of the cell is called the front busbar/content, and the bottom is called the rear contact.

Traditional silicone solar cells use silicone for both these layers, with each layer modified with little amounts of elements that produce different electrical charges.

N-P Type Regions

The portion with the highest amount of electrons is known as the N-type region. And the side with the most positively charged holes or missing electrons is called the P-type region (P-type Silicone). Between these two layers is called the P-N Junction.

And when an N-type and a P-type material fall into contact, free electrons from the N-type material and free holes from the P-type move across this boundary then cancel each other out, and then the electrons fill the holes.

The process described above uncovers the fixed positive and negative charges of the dopant ions that create an electric field, stopping other electrons from moving across the boundary. The electric field acts as an in-built voltage, acting as a one-way valve for charge carriers.

Photons represent a small packet of electromagnetic radiation and get absorbed into a solar cell when sunlight hits the surface. This creates an extra free electron and hole that are then separated by the electric field. The photocurrent is created by pulling both to opposite sides of the cell.

Electrodes can be attached to both sides of the cell to form an electrical circuit to make the electricity flow as long as there is sunlight.

Customisation To Alter The Band Gap

The thing that separates perovskite crystals is how customisable they are. Normal single-junction solar cells can only absorb a small portion of the solar spectrum depending on the material they use. The lowest amount of energy that can be absorbed in a semiconductor is called the band gap.

Semiconductors cannot absorb energy that is less than the band gap, and the energy that can be used from sunlight/photons is no more than the band gap energy. Because of this, most of the energy in sunlight goes to waste when it hits a single-junction solar cell.

With perovskite, the band gap can be changed and stacked on top of one another. These layers can be chemically tuned to absorb different parts of the solar spectrum, resulting in a solar cell that has multiple P-N junctions that produce energy.

These solar cells are then able to extract more energy from a photon and extract energy from a broader range of light wavelengths. Both of which help improve efficiency.

From Single Junction To Multi Junction Solar cells

This is the process that takes us away from the inefficient single-junction solar cell and gives us multi-junction solar cells. And with multi-junction solar cells, we can go beyond the Shockley Queisser Limit of 33% max efficiency, up to roughly 45%.

In theory, we can go much higher than 45% efficiency by adding more and more layers but it would then become too expensive. The way perovskite is intended to be used in the near future is 2 layers, called perovskite tandems that waste less heat when converting sunlight into energy.

We are now starting to see real advancements in the use of perovskites and they are now beginning to surpass the mono and polycrystalline silicon cells in terms of conversion efficiency. 

How Soon Before We See Perovskite In Commercial Use?

While it is already in use in a few areas, there are a couple of things halting the use of perovskite to make commercial solar panels. For a solar panel to be brought o the market, the manufacturers need to be able to give their product a life span and unfortunately, the data is not there yet. 

While there is no doubt we will soon see the type of solar panel we see on rooftops and in fields made from perovskite, there is more data and advancements needed to hit the 25-year-plus life span guarantee.

Where Will We See Perovskite Used First?

We are likely to first see it being used to power lightweight drones as they only have a short life span. We will also see it become common in electric vehicles, and today there is a tesla model with perovskite solar panels.

Many devices, such as solar wristwatches, wearable technology, and small IOT devices (internet of things) will all utilise perovskite technology.

With all new technologies, it is difficult to predict exactly where they will be in the future and perovskite technology is no different in this regard. 

The fastest-growing energy technology on the planet today is solar photovoltaics. I hope soon we can produce cheap and clean energy for everyone.

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