Photovoltaics

The City of Lights

Max and Lily were enjoying their evening at a typical café Parisienne. As the last of the sun’s rays were hidden beyond the horizon, the lights of the Eiffel Tower lit up, giving the city its unique night colours.

“Did you know that back in 2013 there was an illumination ban?” Max started, “all the stores and non-residential buildings had to switch off their interior lights by 1 a.m. at the latest”.

“I suppose the carbon dioxide emissions were reduced, but it must have been a little sad… the city of lights… lightless?” Lily said. “But now, look at this glorious view!” she added, pointing at the twinkling Eiffel Tower and surrounding illuminated monuments and museums. “And they all are powered by the sun. Do you see the fuchsia building over there? Its paint is actually a coating of organic solar cells”.

Max rolled his eyes at Lily and laughed: “Fuchsia? Is that even a colour? And don’t get me started with organic solar cells. Do you know what organic means? Do you even know what a solar cell is?”

Lily sat up straight in her chair and answered his challenge. She started by explaining that a solar cell is a device that absorbs light from the sun, converts it to electric energy which can be used either directly (by lighting a lamp for example) or stored in batteries.

‘An organic solar cell,’ she continued, ‘also called a plastic solar cell, is made of polymers or fullerenes, carbon compounds shaped like a buckyball. And a plastic solar cell has taken over plastic properties: it is flexible, inexpensive and easy to make. And it can be recycled!'

“And it also has an expiry date just like most plastics do!” Max said and pointed out that the traditional solar cells made of silicon were lasting longer and were cheaper too. He then showed her his mobile phone which had an integrated silicon solar cell to charge the battery. Lily also took her mobile phone out and showed off its flexible and fashionable case, made of an organic solar cell. Max made fun of it, as his device was charging faster.  

“But it is not only the energy they provide us with, it is also the energy we consumed to make them” Lily insisted. “Organic solar cells need less energy to be produced and you should take this into consideration when talking about efficiency” said Lily.

She went on talking about a new “army” of materials, perovskites, named after the famous mineralogist Lev Perovski, which have been enlisted in the battle for efficient and sustainable photovoltaics. These are compounds incorporating both organic and inorganic parts in their structures. These materials are generally abundant, sustainable and very efficient.

“Well, if we talk about efficiency, why not use gallium arsenide for our solar cells? That is efficiency! And they are so robust and durable” Max insisted.

“But… but those odd-named chemical compounds can be toxic! They should be kept out of the world!” Lily said almost fuming.

“Indeed” Max said amused “they are the solar cells used in space! Where do you think satellites get their power from? They aren’t plugged into our power grids” he teased her.

Lily, realising he was just pulling her leg, calmed down and smiled. She laid back and looked around at the public buildings; all painted in different colours, including the Eiffel Tower, all gathering enough energy from the sun to illuminate the entire city in a zero emission way.

Max guessed her thoughts and tried to tease her again. “You know, for maximum efficiency we should have painted all the buildings black, because black is the colour that absorbs all the sun rays” he said meekly. 

“I want a sustainable and colourful future” she said, smiling back.