Special Coating Greatly Improves the Performance of Solar Cells

The energy from sunlight falling on only 9% of California’s Mojave Desert could supply the electricity needs of the United States if the energy is efficiently harvested, according to some estimates. Unfortunately, the current generation of solar cell technology is too expensive and inefficient for business applications on a wide scale.

According to Eurekalert, the new services of the American Association for the Advancement of Science, a team of researchers from Northwestern University has developed a new anode coating strategy that significantly heightens the efficiency of conversion of solar energy. A report about the work, which focuses on “engineering” of the interfaces of the organic material of electrodes in large quantities of organic heterojunction solar cells, was published online this week in the Proceedings of the National Academy of Sciences (PNAS).

This progress in solar energy conversion promises to bring researchers and developers of the world to the goal of producing cheaper, more factories and cells easily implemented. These technologies significantly reduce our dependence on fossil fuel for electricity production and also reduce the combustion product: carbon dioxide, a greenhouse gas for global warming.

Tobin J. Marks, Researcher Professor Vladimir N. Ipatieff Chemistry Institute of Arts and Science and Weinberg Professor of materials science and engineering, and Robert Chang, professor materials science and engineering in the School of Engineering and Applied Science McCormick, leads the research team. Other Northwestern team members were researcher Bruce Buchholz and graduate students Michael D. Irwin and Alexander W. Hains.

Of the new solar conversion technologies on the horizon, solar cells made from organic materials such as plastics are attractive because they can be printed cheaply and quickly by a process similar to printing newspapers.

To date, the type of plastic photovoltaic cells most successful is called “bulk-heterojunction cell.” This cell utilizes a layer consisting of a mixture of semiconducting polymers (electron donor) and a fullerene (an electron container) tightly between two electrons – an electrical conductor electrode (the anode, which is usually covered with indium oxide tin) and a metal (the cathode), such as aluminum.

When light enters through the transparent conductive electrode and kicks the layer of polymers that absorb light, electricity flows due to formation of pairs of electrons and holes are separated and are directed to the cathode and anode, respectively. These charges are in motion electric current (current picture) generated by the cell and are collected by two electrodes, assuming that each type of cargo can pass through the layer between the active interest of fullerene-polymers and the correct electrode to carry the load – a major challenge.

The Northwestern researchers employed a laser deposition technique that coats the anode with a thin (5 to 10 nanometers thick) and smooth layer of oxide nikel. This material is an excellent conductor for extracting holes from the irradiated cell but, equally significant, is a major blocker that prevents the electrons to be channeled more misplaced electrode “incorrect” (the anode), which compromise the efficiency of conversion of the cell energy.

In contrast to previous approaches for anode coating, the coating of oxide nickel Northwestern is more cheap, electrically homogeneous and non-corrosive. In the case of cells in the bulk-heterojunction model, the Northwestern team has increased the voltage of the cell to approximately 40 percent and the efficiency of energy conversion of approximately 3 to 4 per cent to 5.2 to 5 , 6 per cent.

Researchers are currently working on tuning the anode coating technique for the extraction of the whole extraction and electron blocking efficiency and moving to production-scale experiments on flexible substrates.