Ada Genavia
Apr 27, 2012

New features in solar material could lead to the next generation in solar technology

The impending scarcity of many valuable resources on our planet has had people searching for and utilizing other energy sources. Although researchers have studied and noted the the viability of wind and water energy, there is another source that proves to be an easy transportable energy solution. Solar energy is a major contender for the energy harvest. With fossil fuels nearing their extinction and becoming more expensive to source, the solar industry has helped to reduce this pricey consumption with the use of photovoltaics (PV) technology. Since the solar industry has come into play, PV technology has had a significant impact on existing green technologies. First generation solar technology -- the silicon PV cell -- was first developed more than 50 years ago at Bell Labs in New Jersey. Based on silicon wafers, this became the first cell with enough power to run everyday electrical equipment. The second generation technology came along as thin film to simplify manufacturing and reduce costs. Although both technologies are highlights in the history of solar energy, silicon wafers are fragile, limiting processes and applications, and thin film proved to be less efficient and more costly.

Third generation solar technology introduces other areas of solar energy sources including tandem cells, dye-sensitized titanium solar cells and organic photovoltaics. Scientists have been involved in extensive research efforts in all of these areas and it is estimated that this third generation will achieve higher efficiencies and lower costs. Organic photovoltaics have proven to be a sought after solar source tool. The cells use organic electronics which entails conductive organic polymers or small organic molecules for light absorption and charge transport. A large amount of light can be absorbed with a small amount of materials when dealing with organic molecules due to their high optical absorption coefficient. Ongoing research is integral, at this point, in finding out what materials would be sufficient and inexpensive for the next step in solar technology. Research conducted by scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory (in collaboration with researchers from Stony Brook University, Seoul National University in Korea, the Max Planck Institute for Polymer Research in Germany, and Konarka Technologies) has done just that. Studies of one of the most efficient organic photovoltaic materials reveal an unusual bilayer lamellar structure that may help explain its excellent ability to convert sunlight to electricity and guide the synthesis of new materials with even better properties.

Structural details of photovoltaic material revealed: The bilayer polymer backbone motif (3D image) is derived from the x-ray scattering pattern.Known by the handle PCDTBT, this material is an example of a “polycarbazole conjugated polymer,” a molecule composed of a chainlike carbon backbone with alkyl side chains. It  is among the best organic photovoltaic materials currently in use due to its amazing ability to move electrons around. The material is also able to convert sunlight to electricity with efficiency as high as 7.2 percent in organic solar cells. Brookhaven physicist, Benjamin Ocko (who led the current research) states, “Despite the fact that this material has been extensively studied, no one has reported detailed structural features to provide a basis for its superior performance.” Understanding this material and its strong performance will help scientists harness its essential attributes. Engineering new materials for a wide range of applications, including displays, solid-state lighting, transistors, and improved solar cells is a sought-after possibility.

This research is a step up in achieving a efficient and cleaner Brookhaven Lab research team members Xinhui Lu, Htay Hlaing, David Germack, and Ben for solar energy.This type of in-depth and collaborative study with different partners elucidates very subtle differences between materials, which gives critical insights into designing next generation solar cell materials. Organic photovoltaic solar cells (OPV) bear a potential development in the search for low-cost modules for the commercial production of domestic electricity. The collaboration of these companies and organizations suggests the importance of PV technology. One of the top funders for this recent research, Konarka Technologies (Konarka), is a world leader in OPV technology. OPV is rapidly emerging as a solar source and Konarka’s current research efforts are exploring new OPV chemistries as well as advances to existing technology. The Department of Energy also recognizes the significance of OPV as it presents a ‘greener’ solution for energy reliability. Amounts of organic materials are relatively small and large scale production is easier than for inorganic materials. Additionally, the vast variety of possible chemical structures and functionalities of organic materials allows research for alternative competitive materials with the PV properties. Included in this variety of chemical structures are polymers, oligomers, dyes and liquid crystals. The development of organic solar cells is definitely on the rise which makes it an easy target for companies to take part on its research.

Another similar project is graphene OPV in which flexible transparent carbon atom films have great potential for a new breed of solar cells. The significant advantages in this development is the cell design, particularly in physical flexibility. The ongoing research for new techniques and discoveries in the solar industry constitutes a significant advance toward the production of OPV. This recent research on the solar material and its new features meets the essential criteria for efficiency, stability and abundance in OPV; this will ultimately have important implications for future organic devices as well as a third generation solar tech milestone.