A new type of polymer solar cell adds to the growing field of transparent solar technology, and offers reasonably impressive efficiency for such a device. Researchers at UCLA have created a cell that absorbs primarily infrared light, allowing much of the visible spectrum to pass through; the cell is 66 percent transparent, with an energy conversion efficiency of 4 percent.
The 4 percent rate seems low compared to the 15 to 20 percent for standard solar panels, but transparent cells are generally stuck in such low ranges. And if the new cells are cheap to produce and actually install on windows, 4 percent won't sound so terrible. The new work's lead researcher, UCLA materials science and engineering professor Yang Yang, said in a press release that "they can be produced at high volume at low cost."
According to the group's paper, polymer solar cells have reached a record efficiency of 10.6 percent, at least suggesting that the materials could compete with more standard solar technology. The new cell involves a photoactive layer sandwiched between transparent electrodes. The photoactive layer is made of a near-infrared light-sensitive photovoltaic polymer (if you must know: poly(2,6'-4,8-bis(5-ethylhexylthienyl)benzo[1,2-b;3,4-b]dithiophene-alt-5-dibutyloctyl-3,6-bis(5-bromothiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4-dione, or, in the interest of brevity, PBDTT-DPP). From the paper: "PBDTT-DPP is a low band gap polymer with strong photosensitivity in the range of 650-850 nm." The top transparent electrode was made from silver nanowire composite films, allowing for solution processing -- a cheap method for fabricating solar cells.
The researchers created 40 of the cells to ensure reproducibility, and found efficiencies ranging between 3.6 and 4 percent. Transparent solar has gotten a lot of attention in recent years, given the obvious appeal of having every sun-facing window producing power even while you stare through it. The economics of covering every skyscraper in energy-producing glass might not work for a while, but there is undeniable potential: in 2010, buildings accounted for 41 percent of all electricity consumption in the U.S.
Image via ACS Nano/UCLA