June 1, 2012 (Source: Solar Nouvus Today) -- Researchers at the University of Florida (UFL) in Gainesville, Florida (US) achieved the highest power conversion efficiency yet for a graphene-based solar cell after adding an organic dopant: 8.6% that is more than for times the efficiency of undoped devices. "In our recent work, we have reduced the graphene's sheet resistance by chemical doping. That's already big," says the lead researcher, Sefaattin Tongay. What's more, after chemically doping the graphene, their devices turned out to be environmentally more stable. In addition, the doping enabled the UFL researchers to adjust the electric field at the graphene/semiconductor junction, allowing them to collect electron-hole pairs even more efficiently. The Florida researchers achieved this record result using "extremely cheap organic solutions and naturally abundant materials," Dr. Tongay adds. Exactly how did the Florida researchers dope graphene solar cells? "The main idea is twofold," Dr. Tongay explains. "Chemical doping reduces graphene's electrical resistivity so that the ohmic loss in the solar cell is minimized. Also during this doping step, we change the Fermi level of graphene in our favor and adjust the strength of the electric field at the interface for improving the charge collection efficiency." The doping level of the Silicon wafer hereby has to be chosen very carefully. Is the wafer too doped, it will reduce the exciton lifetime. Is it doped too little, it becomes too resistive. "Originally we wanted to reduce the resistance of the graphene layer by chemical doping without effecting graphene's optical properties," Tongay says. "We came up with an organic composition TFSA ((CF3SO2)2NH)." The organic dopant has electronegative elements that withdraw electrons from the graphene. "This simple spin-casting method hole dopes the graphene and reduces the sheet resistance of the graphene. But this is just a beginning." Furthermore, a change in the Femi level at the graphene side created stronger electric field at the graphene/semiconductor interface, which in return allowed them to separate the charges more efficiently. "The organic dopant and the good graphene transfer is the magic here," says Dr. Tongay, who believes graphene will defeat indium tin oxide (ITO) in a matter of time. "The organic layer reduces the graphene sheet resistance, adjusts the electric field in the active region, helps to collect separated charges more efficiently and, on top of all, the organic layer makes the whole device environmentally stable which is a common problem in graphene based solar cells." Tongay and his team were elated to achieve a power conversion efficiency of 8.6%. "We all worked on it for a long time. We had plenty of reasons to move on to another project and just give up. But we all were confident scientifically that it would work. Now, we are chasing next generation solar cells and looking forward to bring new to the table," Dr. Tongay says, who thinks 10% efficiency is "doable", but more than 20% "needs a push." His team is currently exploring different device geometries and cheap materials. The latter pursuit being "more adventurous and high risk the high benefit project." Dr. Tongay believes the proposed technology can "easily be optimized and engineered to boost the efficiency to even higher limits" and is confident "the industry will "recognize this right away" and "appreciate graphene's capabilities in combination with cheap Si substrates." However, before graphene-based solar cells hit the market, he says, "We need to optimize how to transfer graphene onto different substrates and improve graphene's conductivity."
This is where there the energy solutions are at. Not robbing them to support already available but uneconomic versions. At 20% and 1/3 the price of current cells they would be a real game changer.
For decades I heard about the newest discoveries that are going to change the world,and then you never hear anything about them again. Tell me about the fish you've caught,when they are in the basket.
I understand what you are saying But understand the absolute stampede happening in the world to be the first to offer a viable 'green' alternative in the west. We invest in silver (most of us) - part of the major future demand for silver will come from energy application. In fact just about ALL of the bull markets (other than gold) have been in energy related commodities (Uranium, REE, Oil, Graphite, certain foods like Corn for bio fuels, and i think Gas will be the next one) - the world is so desperate to find something to feed its energy needs. Every new idea gets us closer - and its important to know what is going on so we can add it to our 'big picture' view when investing.
There are scientists that will twist results to put their name in lights. Many that are just plain mistaken. Journalists that will lie to get a story into the papers. Editors that will distort facts to fill a page. Interviewers that will do anything to create a story, Politicians that will present facts with art to prove a position. All "information" must be looked at with cynical eyes. What is possible in a lab is usually not possible on a commercial scale. I wish all the possibilities just around the corner were in fact possible. 99% are not. One of Murphy's lesser known Laws is "99% of everything is crud."
