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Skip to 0 minutes and 6 seconds There are a number of different ways that we can get the energy from the sun into where we need it in our electronic devices. Some of these are relatively well-established, whereas others are still very much in the development stage. Here, I’ve got a few examples. So this one is a silicon solar cell. Can be produced at a fairly low cost and reasonably large scale. However, it’s not necessarily going to solve all of the energy problems. The next is a small example device here which operates at very high efficiency.

Skip to 0 minutes and 43 seconds Unfortunately, it is also a very expensive type of solar cell, and the materials that are included in its manufacture are fairly rare in the context of the earth, which means that the possibility and the scope for terawatt deployment is very limited. We focus on types of solar cells which are more amenable to that large scale. So next we have some dye sensitised solar cells. These are ones that we work on here and develop here. They are low cost to manufacture. They include only materials which are earth abundant. However, at the moment, they’re not quite efficient enough to be deployed at large scale.

Skip to 1 minute and 31 seconds They’re not cost competitive because of that low efficiency, so we’re looking at ways to increase the efficiency to a point where it can be the case. So also here we work on what are known as organic photovoltaics. In this case, all of the active materials are organic materials. Then we have two contacts, one which is transparent glass, conductive glass, and one which is a metallic contact. Now these can be produced using more conventional printing techniques, which means that using very similar approaches to that, we can see flexible devices, such as the one I’m holding in my hand.

Skip to 2 minutes and 11 seconds These flexible devices can be produced at large scale using conventional printing techniques, which probably gives us the best chance of being able to meet the terawatt challenge. So all the devices which I’ve just introduced you to rely on the same fundamental physical principle, which is the photovoltaic effect. However, the exact way that they get electricity out and into your hands and into your devices does vary.

Types of solar cells

Absorbing the sun

Materials and Solar Cells

All solar cells contain materials that absorb light resulting in the separation of charges, electrons and holes, that can then be extracted to do work. So the types of solar cells are characterised by these energy materials, typically semi-conductors.

Common solar cells are shown below:

  • Silicon solar cell (Si) - there are a wide variety of silicon solar cells from the high performance but expensive crystalline to the much cheaper amorphous silicon cells.

  • Cadmium telluride solar cell (CdTe)

  • Copper indium gallium selenide solar cells (CI(G)S)

  • Gallium arsenide germanium solar cell (GaAs)

The following solar cells are under commercial development, there is however still a lot of research taking place;

We will look in more depth at a dye-sensitised solar cell later in this course.

Terawatt Challenge?

When we think about the Terawatt Challenge, we need to consider a couple of important points about these technologies:

Firstly, how good are they at turning the sun’s energy into electricity for us to use? Are the materials abundant enough to be produced at very large scale? And, of course, are they going to be easy to manufacture?

It turns out that none of these technologies can tick all the boxes, at least not yet. Organic (plastic-based) solar cells do have major advantages when it comes to these last two points, as plastics are typically made from readily available elements, and their flexibility makes them easier to manufacture at high-volume and high-speed.

  • What type of solar cell do you find most interesting?
  • Which type has the most potential for future application?

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How to Survive on Earth: Energy Materials for a Sustainable Future

University of Wollongong

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