A special coating significantly improves the efficiency of the solar cells

A team of researchers from Northwestern University was able to increase the electrical voltage of the cell by forty percent and the conversion efficiency from three to four percent to 5.2-5.6 percent

The energy from the sun reaching an area of ​​only about nine percent of the Mojave Desert in California could supply the entire electricity consumption of the United States if only collected properly, according to several estimates. Unfortunately, current generation solar cell technologies are too expensive and insufficient for large-scale commercial applications.

A research team from Northwestern University has developed a state-of-the-art process for anodic coating that significantly increases the conversion efficiency of solar energy into electricity. An article about this research, which focuses on inducing interfaces of electrodes-organic materials in organic solar cells, was published in the scientific journal "Proceedings of the National Academy of Sciences".

This breakthrough in solar energy conversion promises to advance researchers in the field and developers all over the world towards the goal of producing cheaper, commercial and more applicable solar cells. Such a technology will greatly reduce our dependence on burning fossil fuels to produce electricity as well as reduce the product of combustion: carbon dioxide - a greenhouse gas that leads to global warming.

Among the new solar energy conversion technologies that exist on the research horizon, solar cells composed of plastic-like organic materials are the most interesting because they can be obtained in a cheap and fast process similar to the process of printing on newspapers (roll-to-roll processing). Until now, the most successful type of photovoltaic cell made of plastic is called "bulk-heterojunction cell". This cell consists of a layer containing an exhibition of a semiconducting polymer (electron donor) and a fullerene (electron acceptor) trapped between two electrodes - a conductive electrode (the anode, which is usually indium oxide containing tin) and a metal (the cathode, e.g. an iron).

The fullerenes, discovered in 1985 by Robert Carle, Harold Croteau and Richard Smalley from the University of Sussex and Rice University, are a group of allotropes of carbon named after the architect Richard Buckminster Fuller. The fullerenes are pure carbon molecules and their shape can be spherical ("Bucky balls"), elliptical or tubular. Cylindrical fullerenes are called carbon nanotubes, or Bucky tubes. The chemical structure of fullerenes is similar to that of graphite, but unlike graphite they may also include pentagonal (or octagonal) rings that prevent the entire molecule from being planar.” – from Wikipedia].

When a light beam strikes the polymer layer inside the conductive electrode, an electric current is created due to the formation of electron and electron-hole pairs that separate and migrate to the cathode and anode, respectively. These traveling charges are the electric current (photonic current) generated in the cell and stored using the two electrodes, assuming that each type of charge can easily cross the interface between the active polymer-fullerene layer and the corresponding electrode to transfer the charge - a very serious challenge.

The researchers used a laser deposition process to coat the anode with an extremely thin layer (5-10 nanometers thick) and as uniform as possible of nickel oxide. This material is an excellent conductor for creating electron-holes from the irradiated cell, but of equal importance, it is also an effective blocker that prevents "stray" electrons from reaching the wrong electrode (the anode), thus significantly damaging the energy conversion efficiency of the cell. In contrast to earlier approaches to anodic coating, the nickel oxide coating of the aforementioned research team is cheap, uniform and non-corrosive. In the case of a preliminary model for the plastic cell, the research team was able to increase the electrical voltage of the cell by forty percent and the conversion efficiency from three to four percent to 5.2-5.6 percent. The researchers are now continuing and improving their coating method for increased efficiency of the passage of electric charges and the creation of electron holes.

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