More cells in the street, more use for the heat (Photographer: David Goehring).
Science

Printable solar power cells could soon be a thing

by Joshua Green

The threats that global warming are, without doubt, some of the biggest challenges that this generation and the ones after it will face. The economic, political and especially environmental issues that are related to global warming often combine with issues of living on a world with finite resources. Efforts to further study renewable energy sources have therefore been fuelled by the demands. One of the most popular forms of renewable energies is solar power. Solar power involves using solar cell panels on top of roofs or anything that has a decent chance of catching those vital rays from the sun.

In a nut shell a solar cell works by collecting photons (of which light is made of) that travel from our sun. The material that the cell is made from is usually silicon and the light excites electrons from the silicon atoms. These electrons can make their way to electrodes and therefore the devices produce electricity. Due to the gigantic usage of silicon in both the solar cell industry but primarily in the semiconductor industry the cost of producing very high quality silicon has gotten lower and lower.

Another form of solar cell panel is a perovskite solar cell. These cells work in a similar fashion to silicon ones but the active material is formed from a layer of crystals thousands of times thinner than a human hair. The material is low cost and can be made into a liquid form which means these solar cells can be printed onto surfaces. The problem is that these types of cells lack a good mechanism to retrieve the excited electrons. An electron selective layer (ESL) is needed to get the electrons to flow in the circuit. These ESLs are usually a power that has to be heated to very high temperatures. This is a problem for manufacturing because if you heat up to above 500 degrees C the glass or silicon chip you are printing on will melt.

Researchers at the University of Toronto, led by Dr Harien Tan, have discovered a way of applying this crucial ESL using temperatures much lower than 500 degrees C. Tan and his team of scientists have come up with a new chemical reaction that enables a nanoparticle ESL, stored in a solution, to be used if heated at 150 degrees C when applied onto the desired surface. The ESL and perovskite layer are bonded together with help of a layer of chlorine atoms inbetween. Thanks to this the efficiency (that is the light gathered compared to the electricity produced) reaches a high value (for cells) at 20%. It was also reported that the solar cells remained stable after 5000 hours of a use which is a usual problem with perovskite cells.

The ambition is to combine silicon and perovskite to create hybrid devices that have the capacity to reach 30% efficiency and higher. This would enable solar cells to be viewed as more economically viable and would lead to an increase of solar cells out there. As most reading this will agree, this can only be a good thing when we look ahead at the challenges that we will face.

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