Harnessing the sun's infrared spectrum in large-area photovoltaic devices

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The sun's rays carry to the earth's surface ten thousand times more energy than we consume each day via all sources of production - nuclear, fossil, hydroelectric power combined. The entirety of North America's energy needs could be met by covering an area 200x200 kilometers with 20%-power-efficient solar cells. While this is a small fraction of the North American continent, it is a huge area for an electronic device. Today, these tend to be made from crystalline semiconductors such as silicon, gallium arsenide, or indium phosphide. Building devices requires cleanroom conditions and a sequential process flow employing methods such as optical lithography, dry etching, and evaporative metallization. To build square kilometers of optoelectronic device within such a paradigm is unimaginable. Flexible optoelectronics brings large device areas into the realm of the imaginable. Plastic optoelectronic devices, made based on solution-processing and related coating technologies, can be made using a roll-to-roll process akin to the printing of newspapers. Start-up companies have already begun commercialization of the technologies to make large-area printable solar cells. Suppliers of coating equipment such are adapting their established expertise in the direction of large-area printable optoelectronics. The entire field is waiting for a more efficient solar cell. Today's plastic solar cells capture only the sun's rays which lie in the visible wavelength range. In fact, half of the sun's power reaching the earth lies in the infrared wavelength range. We reported in early 2005 in the journal Nature Materials the first-ever plastic solar cell which captures the sun's infrared rays. This first-ever device was not efficient. In the present project, we propose to pursue the maximization of the power-conversion efficiency of infrared-sensitive plastic photovoltaics. We target 1% power conversion efficiency in the infrared as proof-of-principle goal which will enter our technology into the realm of commercial relevance.