Organic Photovoltaics Absorb From Near Infrared Frequencies

A research group has developed organic nanostructures photovoltaics that can absorb photons near the infrared frequency.

Ewing, NJ | 4 January 2006 — Global Photonic Energy Corporation (GPEC), developer of organic photovoltaic (OPVtm) technology for ultra-low cost high power solar cells, announced that the company’s research partners at Princeton University and the University of Southern California (USC) have achieved a new record in an organic solar cell that is responsive to light in the near infrared (NIR) range of the solar spectrum. NIR radiation is invisible to the human eye.

Many so-called “night vision” devices operate by sensing infrared light which is emitted by warm objects and makes up a substantial portion of all energy reaching the earth from the sun. Under only NIR radiation, the Princeton solar cell would appear to be generating power in the dark — as the human eye is only sensitive to visible light.

This latest achievement is the highest level of conversion performance yet achieved for an organic solar cell in the IR portion of the solar spectrum. The Company’s researchers detail this latest achievement in the December 2 issue of Applied Physics Letters.

The Global thirst for energy is continually expanding. Renewable energy sources have experienced rapid growth in recent years as costs have improved. Global solar cell production has grown over 20% annually for the last 20 years, reaching sales of $6 billion in 2004. This strong growth has resulted in a world-wide shortage of semiconductor silicon driving 2005 solar cell prices higher. Cost is a critical factor in the continued expansion of the solar cell industry. Currently, solar-generated power is four to six times more expensive to consumers than coal-generated power.

Silicon crystals are too expensive as a starting material for making photovoltaics cells. The development of organic photovoltaic materials holds the potential for much cheaper photovoltaics. These Princeton and USC researchers (see below) are not only pursuing organically based photovoltaics but they are also pursuing the development of much higher efficiency photovoltaics. The odds are developing a way to double or triple the conversion efficiency of organic photovoltaics will not increase costs per square meter of materials anywhere near as much. So cost per unit of energy produced will drop.

Recent efforts have focused on the use of “organic” materials. Organic semiconductors contain the ubiquitous element carbon and are capable of achieving ultra-low cost solar power generation that is competitive with traditional fossil fuel sources. Organic materials have the potential to achieve ultra-low cost production costs and high power output. The materials are ultra-thin and flexible and can be applied to large, curved or spherical surfaces. Because the layers are so thin, transparent solar cells can be applied to windows creating power-generating glass that retains its basic functionality.

GPEC sponsors research by Professor Stephen R. Forrest at Princeton and Professor Mark E. Thompson at USC.

Professor Forrest’s research team has focused on organic “small-molecule” devices that are assembled literally a molecule at a time in highly efficient nanostructures. These devices have layers and/or structural elements that can be extremely small — at only 0.5 billionth of a meter thick and can be applied to low-cost, flexible plastic surfaces.

These scientists want to boost absorption of photons near the infrared frequency range because that is where much of the energy in sunlight is found.

One challenge for organic solar cells has been the efficient capture and conversion of sunlight. Sunlight consists of photons (particles of light) that are delivered across a spectrum that includes invisible ultraviolet (UV) light, the visible spectrum of colors — violet, indigo, blue, green, yellow, orange and red — and the invisible infrared or IR spectrum. The amount of incoming photons across the UV, visible and IR spectrums is about 4%, 51% and 45%, respectively. The photons absorbed by a solar cell directly impacts the power output. To achieve high power output, solar devices must take advantage of as much of the solar spectrum as possible. Typical organic solar cells absorb only a fraction of the visible portion of the solar spectrum. In fact, the best organic solar cells absorb and convert only about 1/3 of the total available light utilizing primarily the visible portion of the spectrum.

“This latest device demonstrates that significant power can be harvested from the IR and near-IR portion of the solar spectrum.”, said Dr. Stephen R. Forrest. “In fact, this novel approach has the potential to double the power output of organic solar devices with power harvested from the near-IR and IR portion of the solar spectrum. ”

“With this approach we are well on our way to power levels exceeding 100 watts per meter”, Forrest concluded.

Imagine organic photovoltaics coating windows especially in hot climates. Instead of letting in the infrared frequencies the photovoltaics convert those photons to useful electricity. So instead of heating a building and thereby increasing the demand for air conditioning the photovoltaic coating could keep out heat and turn it into electricity that would power air conditioners.

In the longer run imagine nanomaterials-based photovoltaic coatings that could adjust how much electricity they let into a room or into a car depending on whether a human was in the room or car. When a human was present the material could become transparent to allow ing lighting or provide the ability to look outside. House and car windows could be turned dark or transparent by dynamically changing nanostructures. When no one was in a car or house room the windows could become dark and that would mean the nanocoatings were absorbing the light that hit them and turning them into electric to charge batteries (which of course will be made from some nanomaterials as well). So on a hot summer day your car’s seats wouldn’t get as hot. Also, the inside trim wouldn’t degrade as rapidly due to sun damage.

GPEC is funded by electric power industry venture capitalists Kuhns Brothers.