DELFT - The 133rd Geneva International Motor Show in March next year will open with a unique attraction: the first car with a solar cell coating and with solar cells on the seating material and windows that can be used to generate atmospheric lighting and charge up electronic equipment.
The car seats and the windows are covered with a layer of super-thin and flexible solar cells. These generate every desired colour of atmospheric lighting, which can be called up with the press of a button, and can also charge up equipment such as mobile phones and computers.
These super-thin, light, flexible and cheap to produce solar cells with an unprecedented energy yield, can capture most colours in sunlight and efficiently convert these into electricity. They are the result of years of development by Delft University of Technology and the University of Amsterdam with collaboration from Toyota for the car-specific applications. These solar cells are ideal for use on surfaces where there is little space, which are not straight or that must be able to move flexibly. They therefore have a wealth of possible applications, such as the outside of cars, clothing and the packaging of foodstuffs. If food packaging covered with a layer of these solar cells is charged with light from the supermarket, then the package can be connected to the manufacturer’s database with a single swipe to display information about the origin and freshness of the product and how to prepare it. ‘Our project was aimed at developing materials that are cheap and simple to process with solvents’, says Prof. Laurens Siebbeles from Delft University of Technology, who was already involved in the first studies into this new generation of solar cells back in 2019.
Siebbeles talks about newly developed materials that convert light into electricity with a very high efficiency by making use of special processes that do not occur in the standard solar cell. The material consists of different layers, each of which is just several atoms thick. The solar cells are therefore 1000 times thinner than silicon solar cells that are also less flexible and heavier.
This ultra-thin property of the material layers is achieved through the process of chemical vapour deposition. Siebbeles: ‘In the gas phase, you add molecules or atoms to the gas that are subsequently deposited in a layer on a surface. Another method is to throw materials into a solution, mix this and then separate the layers from each other using ultrasound. Initially, we preferred the chemical vapour deposition method because, although it is expensive, it yields a higher quality than the dissolving method.’
The incoming sunlight is absorbed in the layers and through a correct combination of these, the positive charges move to one side, and the negative charges to the other, giving rise to an electric current. The materials have been developed in such a way that each light particle (photon) liberates several charges, whereas usually, each photon liberates at most a single charge. Due to this difference, the ultra-thin solar cells generate more electricity than normal solar cells. The yield is 44%, which is far higher than the maximum 33% using a standard solar cell.
One of the most fantastic results of these new solar cells is their ability to recycle light. ‘If this material is applied, for instance, to your seating furniture, then it can repurpose the light that falls in through the windows or from the lighting in the room. Normally, the energy in that light is instantly lost, but because it falls on the seating furniture, it charges up the solar cells and can be reused, for example, to power a reading lamp or to charge your mobile phone.’