Sprayed-on or printed solar cells

Let's paint the roof with special paints and we'll have a home power plant... This vision is not so awkward after the announcement that scientists have built a solar cell based on Colloidal Quantum Dot (CQD) films with a record-breaking efficiency of 7%, about 40% higher than that of the best previous devices using CQDs.

Although commercial cells based on traditional silicon technology have efficiency of 15-20%, which is up to three times higher than in the case of the new achievement, the sharp increase in CQD cell efficiency promises a number of interesting applications. They will result from the way of the production of the new cells, with the use of special paints or even just by printing using inkjet printers.

a) diagram of the solar cell made ​​out of colloidal quantum dot film
b) cross-section photographed by a scanning electron microscope

(source: physicsworld.com)

 

 

Colloidal Quantum Dot (CQD) films employ the recent developments in nanotechnology, particularly the phenomena taking place in so-called "Quantum dots" - ultra-thin semiconductor layer with unique light-capture properties. Quantum dots is an integrated thin film of thickness several to tens of nanometers, divided into cells ( "dots") of similar dimensions. It is worth to note that the wavelength of visible light ranges from 400 to 700 nm and 1 nanometer is one millionth of a millimeter.
 

 

The capturing of photons that increase the energy of electrons is the basis of all solar cells. The small surface and thickness of a "quantum dot" restricts the free movement of particles. By analogy to a shooting gallery, the photon has a greater chance to hit the immobilized electron instead of one constantly vibrating in a haphazard manner - hence the greater efficiency.
 

 

The problem is the selection of materials and mastering the technology, but the prospective performance levels are impressive, especially when combining existing and quantum technologies. In October, the United States Air Force commissioned Magnolia Solar to develop nanotechnology solutions for reaching the efficiency of solar cells intended for the defense and space industries close to 50%!

The total power used by humans is only about 0.02% of the solar radiation power reaching the Earth. The solar energy received by the Earth during six months equals the amount of energy contained in the estimated resources of the currently used fuels - coal, oil, gas and uranium. The total energy that reaches a horizontal surface throughout the year ranges from 600 kWh/m²/year in the Nordic  countries to more than 2500 kWh/m²/ year in central Africa. All the energy of solar radiation absorbed by the Earth, also used in any form by plants and animals, is transformed into heat and then emitted as infrared radiation into outer space. Development of a new generation of photovoltaic cells will allow for better absorption and use of solar energy.