Nanotechnology for Combatting Climate Change: Renewable Energy

While there are many renewable energy technologies out there which are being used in the fight against climate change, solar cells are by and far the most widely commercialised technology.

Solar cells come in many forms and new advancements in their power conversion efficiencies (PCEs) are always coming to the fore and new technologies are always hitting the market—be it from new materials or new solar cell architectures (which can be anything from thin film cells to printable cells or tandem/multi-junction cells).

In recent years, the desire to improve efficiencies while reducing the size of solar cells and/or making them more flexible so that they can fit in traditionally difficult places to install, has led to an increasing interest in nanomaterials.

The small scale of nanomaterials is helping to realise smaller cells, while the inherent flexibility of some thin film nanomaterials is being exploited for creating solar cells that can conform to different surfaces.

However, the main area of interest is that nanomaterials with either excellent electronic properties or light absorption properties are helping to boost the PCEs of solar cells compared to when bulk materials are just used.

Here we look at what innovation is happening in real-world solar applications, and not just in academic studies.

Innovation in Quantum Dots

Quantum dots are ultra-small 0D materials (electrons are confined in all directions) that have excellent light absorption (and light emitting properties). Usually on the scale of 10 to 100 nm in size, quantum dots generate energy when light is applied to them, making them suitable for solar harvesting applications.

Quantum dots have become popular for a range of light-based applications recently, such as in TV screens, but they have also gathered significant amounts of interest in the solar cell space, with companies already bring quantum dot solar cells to market.

One company who has been making quantum dot solar cells is Quantum Materials Corp via their subsidiary company Solterra Renewable Technologies. These solar cells are a combination of polymeric materials and quantum dots.

Another example of commercial activity has come from Nanoco. Nanoco are a producer of quantum dots and have been working with the Japanese company Tokyo Electron to jointly develop nanomaterial PV films. The team at Nanoco have also been closely working with academia to develop thin film absorber layers for CIGS solar cells, but there has been no commercial news yet beyond academic studies.

Thin Film Solar Cells

Thin film solar cells have become an increasingly popular area of research because they are thinner and more flexible than traditional, bulkier, solar cells so they can be installed in more areas (including the sides of buildings).

Thin film solar cells utilise materials that are used in bulkier solar architectures (silicon, perovskites etc) but in a much thinner form. Many of these layers that are built on top of each other are on the nanoscale and the technologies required for the deposition can sometimes be nanofabrication methods. So, while some thin films may not be made up of a nanomaterial in the traditional sense, they often fall into the nanoscale realm because of how thin the layers are.

Nanosolar have created a very thin inorganic CIGS (Copper, Indium, Gallium, Selenium) solar cell that uses and aluminium substrate with a thin CIGS layer deposited as a nanoparticle ink. The use of inks in solar cells is growing because it allows much thinner solar cells to be created. The PCEs so far have a certified 17.1% PCE, which is low compared to normal CIGS cells but is quite high for a thin film solar cell (as they tend to be lower in general).

Another company that is commercially producing thin film solar cells is Oxford PV. They use perovskites—which is one of the most promising materials for solar cells with their high theoretical efficiencies—in a thin film form. Oxford PV have created both single junction and tandem thin film cells, with the highest PCEs recorded to date of 29.52%—which is a record for commercial solar cells that has been certified by the National Renewable Energy Laboratory (NREL).

A Growing Interest in Graphene Solar Cells

Graphene has been gathering interest in a lot of industries and has started to penetrate many advanced technology sectors. Graphene has several properties that make it an ideal material for improving the PCE of different solar cells and there have already been several commercial developments surrounding graphene-enhanced solar cells.

The first notable development in graphene-enhanced solar cells came from a collaboration between ZNShine in China and Bharat Heavy Electricals Limited in India. The resulting product is a graphene coated solar cell, where the graphene coating acts a self-cleaning mechanism for removing the dust and sand off the cell in dry environments.

It’s not an application where graphene is used directly to improve the electronic properties of the cell, but graphene is utilised in a way that helps to ensure that the solar cell runs optimally (by keeping the surface free from light blocking particles). ZNShine now produce graphene coated solar cells for different markets.

Another company that has produced graphene solar cells is Freevolt in the U.S. These solar cells have targeted the residential housing market, with the company S2A modular also using these solar cells in their self-sustaining homes.

One of the latest developments has come from the UK company, Grafmarine, who are building graphene solar cells for ships that can withstand harsh marine environments. These extra tough solar cells, termed the ‘nanodeck’ is currently in the prototype stage but is currently undergoing a lot of trials that will see it progress to greater levels of commercialisation in the near future.

While it’s not a commercial scale development, there is also now a solar farm being composed of large area graphene-perovskite (GRAPE) cells being trialled out in Greece. The solar farm currently consists of 9 solar cell units, each of which have 40 modules, and is set to produce up to 546 kWh per year.

There will likely be many more developments in the future for both graphene and other nanomaterial-enhanced solar cells. As the technologies mature, and there becomes a greater need for higher efficiencies and smaller solar units, there’s likely to be a greater need for nanotechnology to provide these benefits.

Read the original article on Nano Magazine.