Perovskite Solar Cells: The Future of Energy
For years the world has been using age-old fossil fuels for most of our energy. Large corporations have kept a tight grasp on their right to exploit fossil fuels and have ignored any negative environmental consequences. Although the last few decades has shown promise in a rise to more renewable options such as wind and solar, they have all proved to be largely insufficient and costly when compared to traditional methods such as coal or natural. However, that is soon to change with the introduction of perovskite solar cells.
Perovskite solar cells are far cheaper and efficient than traditional solar cells with recent devices reaching over 23%, as of June 2018 and continual increases in their power conversion efficiency. Since they are relatively new, their rapid improvement has been admired by the photovoltaic world and academic world with a great opportunity for further research into the physics and chemistry behind perovskites.
But first,
What is a Perovskite?
Found in the Earth’s mantle, perovskites are minerals that were first discovered in the Ural Mountains by Russian mineralogist Gustav Rose in 1839 and were named after Lev Perovski (who was the founder of the Russian Geographical Society).
Essentially, a perovskite is composed of calcium, titanium, and oxygen in the form of CaTiO3. Similarly, a perovskite structure is a compound that has the form ABX3 and the same crystallographic structure as perovskites.
Depending on the atom composition in the structure, perovskites can have impressive properties such as superconductivity, giant magnetoresistance, spin-dependent transport (spintronics) and catalytic properties. They represent an interesting sandbox for physicists, chemists, and scientists alike to explore!
How do they work?
First, some simple chemistry.
An atom is built-up of positive protons along with neutrons in its center or nucleus. This nucleus is surrounded by negative electrons. Electron flow is also how energy is created with a circuit being a simple loop with electrons actively flowing which charges you phone or powers your desktop.
Now, here comes the sun (do do do doo.)
Now traditional solar cells work by allowing photons, or particles from light, to hit the surface of the solar panel which knock electrons free from a negatively charged semi-conducting material (usually silicon coated with an element to add more electrons). We call this layer the N-level.
Once the electrons are knocked they want to flow up to the P-level, which is the inverse of the N-level and is positively charged, attracting free electrons. However, the PN junction between the layers only goes one way and is not allowing electrons to flow freely from the N-level to the P-level.
Instead, there are thin metal fingers on top of the cell where electrons are collected. From there, they flow through a wire going down to the P-level. Once they reach the P-level the electrons can flow through the PN junction and complete the loop, making the circuit.
As the electrons flow through the wire, they are creating a circuit and are creating a current which is how solar cells generate electricity. Combining hundreds of these cells is what creates the solar panels we see and use today. (Click here for a fun video explanation!)
When fabricating a perovskite solar cell, the perovskite mineral replaces the P-level and becomes the initial contact of sunlight rather than a traditional silicon doped P-layer.
Why are they so important then?
By now, you’ve probably been fascinated by all of the amazing properties of perovskites. However, for those of you who are not material scientists, there is more stuff to tingle your taste buds.
Perovskites were first successfully used in solid-state solar cells in 2012 and since then have grown and gotten better at an exceptional rate. The two main reasons why perovskites have attracted such prominent attention are cell efficiency and open-circuit voltage.
Cell Efficiency
As explained by the grace of Wikipedia,
Solar cell efficiency refers to the portion of energy in the form of sunlight that can be converted via photovoltaics into electricity by the solar cell.
As visible in the graph above (which uses data taken from the NREL solar cell efficiency chart), perovskites have grown tremendously in 4 years since their breakthrough in 2012.
As of June 2018, they have even surpassed other thin-film, non-concentrator technologies including Cadmium Telluride(CdTe) and Copper Indium Gallium Selenide(CIGA) making them the superior solar cell, second only to the traditional Crystalline Silicon solar cells. But with their stagnant increase in efficiency, it won’t be surprising to see them surpass silicon cells soon enough.
Open-Circuit Voltage
Open-circuit voltage(VOC) is the maximum voltage available from a solar cell at zero current. Essentially it’s the voltage when the solar cell is not connected to a circuit or load and isn’t losing voltage across a resistor.
In terms of solar cells, an open-circuit voltage can be used to understand how much of a photon’s energy is lost in the conversion process from light to electricity. In the case of perovskites, they regularly exceed 70% photon energy utilization, meaning they can convert 70% of photon energy into electricity.
Although 70% doesn’t seem phenomenal, standard organic-based solar cells are only able to utilize 50% of the absorbed energy. Plus, perovskite solar cell’s energy utilization is only bound to grow with further research and time and is close to competing with state of the art technologies such as CIGA.
All at a significantly lower price and with the potential to grow even cheaper and fall below silicon solar cell prices.
This is Great…But What’s the Catch
The biggest problem holding perovskites back is a long one. No literally.
Perovskite solar cells suffer from long-term instability. From external factors such as water, light, and oxygen, and internal factors such as heat, perovskites degrade over time. The longest reported perovskite stability is only 1 year and not ready for large scale commercial use. For a complete explanation of the causes check this out!
To realistically compete with silicon solar cells, perovskites would need to last 25 years in outdoor conditions to be marketable and have acceptable time cost efficiency. However, over the years various strategies have been used to improve stability. From changing component choice by using mixed inorganic solutions, surface passivation, and using lead alternatives.
What Now?
Although these problems are apparent right now, it’s only a matter of time till they get solved. With Perovskite’s HUGE potential and opportunity of research, it’s bound to achieve the low cost-per-watt, high efficiency, long lifetimes, and low manufacturing costs that it needs to be commercial.
Key Takeaways
- Perovskite Solar Cell has tremendous potential with research and engineering.
- Perovskite Solar Cells are superior to almost all other solar cells with their efficiency growing at an alarming rate.
- Although Perovskite Solar Cells currently lack long-term stability they will ready commercially very soon.
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Hi! I’m Sabeeh and I’m a curious 17 year super passionate about emerging technologies such as artificial intelligence, brain-computer interfaces, gene-editing, and more. I would love to know more about you!
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