Organic film promises improved solar cells
By Nolan Fell, Electronics Times
Aug 15, 2001
URL: electronicstimes.com
A German-British team has produced an organic thin film photovoltaic device with a quantum efficiency as high as 34%.
Reporting their work in Science, researchers from Cavendish Laboratory in Cambridge, Cambridge Display Technology and the Max-Planck Institut in Mainz combined the liquid crystal hexa-perihexabenzocoronene (HPBC) with a perylene dye in a thin film.
As well as supporting potentially high efficiencies, the process is simple and could produce organic photovoltaic devices very cheaply.
The two chemicals separate vertically as they solidify out of a solution, creating the exciton structure necessary to convert photon energy into electrical charge. This separation eliminates the need for a series of evaporation and lamination steps in the production of a organic photovoltaic, reducing costs.
The HPBC-perylene structure achieved a quantum efficiency — the ratio of light absorbed to electrical energy produced — of 34% using light at a wavelength of 490nm.
But across the visible spectrum, the efficiency is about 1%. Inorganic photovoltaic cells have efficiencies around 20%.
Lukas Schmidt-Mende of the Cavendish Laboratory said: "We spin coat a blend of the materials, which have vertical separation. They create, more or less, the perfect photovoltaic structure. But they do not have a sharp interface, more like a grading. The morphology is very important.
"An ideal photovoltaic cell would have a network of these materials. We can build up stacks with a high charge carrier mobility."
The distinct advantage of polymers over inorganic photovoltaic cells is the potentially low cost of production. But efficiencies still need to be improved significantly. Organic materials are also likely to deteriorate faster than inorganic ones, so the lifetime of the cells will be shorter.
"The work is still at the beginning," said Schmidt-Mende. "We need to find a means to better control the morphology and of stacking the HPBC. Even if these cells needed to be replaced every five years, they will be so cheap that it shouldn't matter. If we can improve the efficiency, I think they have a chance of replacing crystalline cells." |
