Solar Energy for everyone?!
You see those little things in the dish. They may seem small but those things are called perovskites and they have taken the solar cell industry by storm. They are cheap, easy to produce and very flexible in their applications. Their efficiency at converting light into electricity has grown faster than that of any other material and could even outperform the most common solar cell material, silicon.
WHAT?!!! Silicon? No way!
… But there is still use for Silicon. Just wait and see.
What are Perovskites?
Technically, a perovskite is a type of mineral that was first found in the Ural Mountains and named after Lev Perovski (who was the founder of the Russian Geographical Society)… so yeah this isn’t some crazy mineral that I found.
A perovskite structure is any compound that has the same structure as the perovskite mineral. The mineral is composed of calcium, titanium and oxygen. It looks a little something like this:
The perovskite lattice arrangement is represented in multiple ways. The simplest way to think about a perovskite is as a large atomic or molecular cation (positively-charged) of type A in the centre of a cube. The corners of the cube are covered by atoms B (also positively-charged cations) and the faces of the cube are occupied by a smaller atom X with negative charge (anion).
What applications does it have for clean energy?
Because of their unique crystal makeup, perovskites often display a number of interesting properties like:
- giant magnetoresistance
Also, a bunch of different elements can be combined together to form perovskite structures.
It wasn’t until 2012, researchers first discovered how to make a stable thin-film perovskite solar cells with efficiencies over 10%, using organic-inorganic lead halides as the active (light-absorbing) layer. Since then, the efficiency of perovskite solar cells has skyrocketed.
Conventional silicon solar cells require an expensive, multi-step manufacturing process that utilizes a lot of energy. Perovskite solar cells, on the other hand, can be manufactured using a simple solution deposition technique for a fraction of the cost and energy.
What Issues do Perovskites Face?
The biggest issue is long-term instability. This is because the material can degrade because of external factors like water, light, and oxygen. Also because of degradation due to heating.
Several strategies like using mixed-cation systems are being proposed to improve long-term stability.
For example, stability has also been improved through the use of surface passivation (semiconductor surface is rendered) and by combining 2D-layered perovskites with conventional 3D perovskites.
One of the biggest challenges is that the thickness of a perovskite layer should not exceed several hundred nanometers, but at the same time a thin perovskite absorbs less amount of incident photons from the Sun.
This is where we can use Silicon Nanoparticles for better light absorption.
Silicon Nanoparticles to the rescue😎
I read this research paper which explained how an international research group improved perovskite solar cells efficiency by using silicon nanoparticles. The research paper is really technical but here’s the gist of the research:
These nanoparticles can trap light of a broad range of wavelengths near the cell active layer. The particles themselves don’t absorb light and don’t interact with other elements of the battery, and this also helps with maintaining its stability.
We can enhance light harvesting properties of the absorbing perovskite layer without increasing its thickness. This is possible due to metal nanoparticles.
These particles allow for better light absorption due to surface plasmon excitation but have significant drawbacks. For example, they absorb some energy themselves, resulting in them heating up and damaging the battery.
Silicon nanoparticles work better because dielectric particles don’t absorb light, so they don’t heat up. They are chemically inert and don’t affect the stability of the battery.
These particles can also absorb more light of a wide range of wavelengths. Due to special layout characteristics, they don’t damage the structure of the cells. This allows us to enhance cells efficiency by up to almost 19%.
Silicon nanoparticles have already surpassed plasmonic ones. In their research, they used MAPbI3 perovskite, which allowed them to study in detail how resonant silicon nanoparticles affect perovskites solar cells. Apart from that, the nanoparticles themselves can be modified in order to enhance their optical and transport properties. Silicon nanoparticles are also very inexpensive and easy to produce.
That basically means that this method can be easily incorporated in the process of solar cells production!!!
Unique Perovskite with Silicon
Another idea with Silicon and Perovskite solar cells is marrying the two.
By sprinkling a small amount of the rare earth metal ytterbium into standard cesium- and lead-based perovskite, we can also build a perovskite tandem with a different, simpler architecture. Like conventional perovskites, the ytterbium-doped version absorbs blue photons, energizing electrons in the material. But these electrons aren’t turned into current. Instead, they immediately pass their energy to the ytterbium atoms, which re-emit virtually all of it as near-IR light.
Most of these photons zip into the silicon cell below, which absorbs nearly all their energy and efficiently converts it to electricity, losing very little as heat.
We can use a common solar cell–growing technique known as vacuum deposition to create thin, smooth layers of ytterbium-doped perovskite on roughly 14-centimeter silicon solar cells. The technique coats the miniature glass mountain range with an even perovskite film.
In the resulting tandem, nearly all the blue light absorbed by the perovskite is converted to near-IR photons. This enables it to convert 32.2% of the energy it absorbs as sunlight into electricity.
Solar Energy = Future
With all these interesting advancements and research, it’s really exciting to see that we can finally have cheap, scalable solutions for more renewable sources of energy.
Specifically, Perovskite Solar Cells and Silicon Nanoparticles really excite me because I really think these will soon become commercialized for cheap and really efficient energy.