Almost exactly a year ago we reported that UCLA researchers had developed a promising transparent solar cell that offered the possibility of windows that could generate power. That team of researchers hasn't been idle in the year since: on Tuesday, UCLA reported that they've nearly doubled the efficiency of the original solar cells.
The research, the most recent results of which were published Friday in the journal Energy & Environmental Science, involved taking two layers of transparent solar cell "tuned" to slightly different frequencies of near-infrared light. Near-infrared is a color of light whose wavelength is too long for human eyes to register it. These photovoltaic cells capture near-infrared convert it to electrical power, while allowing most of the shorter wavelengths of light in the visible spectrum to pass through. Hence, transparent solar cells.
Last year's effort, headed up by Yang Yang, Professor of Engineering at the UCLA Henry Samueli School of Engineering and Applied Science, produced solar cells that operated at around 4 percent efficiency, meaning that only 4 percent of the sunlight that falls on them is converted to electrical power. That's promising for a radically new technology, but still far less productive than even the most inexpensive solar panels: thin-film and amorphous silicon solar panels bottom out at around 6 percent efficiency.
But by laminating two layers of near-infrared photovoltaic material, Yang and his team were able to boost their (now semitransparent) solar cells' efficiency to 7.3 percent, raising the possibility that a new generation of moderately efficient transparent solar panels may be ready for prime time.
"Using two solar cells with the new interfacial materials in between produces close to two times the energy we originally observed," said Yang in a UCLA press release. "We anticipate this device will offer new directions for solar cells, including the creation of solar windows on homes and office buildings."
Even though 7.3 percent efficiency is still lower than that offered by high-grade photovoltaic panels, that may not matter much if the transparent cells can be manufactured in quantities large enough that they could start replacing windows on a broad scale. Even 7 percent is more efficient than the zero percent power conversion those windows now offer. And Yang's teammate Chun-Chao Chen, primary author of Friday's paper, points out that the cells are fabricated at low temperatures. That means that the process may be easily replicable on a massive scale.
Yang says the cells can be tinted in gray, brown or green, expanding the range of potential architectural applications. He also points out that the breakthrough offers the possibility of photovoltaic smartphone and tablet screens, though at 7.3 percent efficiency, you'd probably have to leave your phone in the sun for a few days to charge it fully.
Still, though, exciting news for people wanting to generate power with our windows!