New invention: Solar cells are made entirely of carbon

Stanford University scientists built the first solar cell made entirely of carbon, promising to replace the expensive materials used in photovoltaic devices today.

The results are published online in ACS Nano (American Chemical Society Nano).
Zhenan Bao, a chemical engineering professor at Stanford University, said: 'Carbon is capable of providing high performance at a low cost . ' 'To the best of our knowledge, this is the first evidence of an active solar cell that has all the components made of carbon. This research was built based on previous work done in our lab '.

Unlike hard silicon solar panels used on many rooftops, Stanford University's thin film is made of carbon materials that can be painted over the roofs.'Perhaps in the future we can see carbon solar cells painted on the surfaces of buildings, on windows or on cars to generate electricity.'

'Paint technology is also likely to reduce production costs,' said Stanford graduate student Michael Vosgueritchian, co-author of the study with postdoctoral researcher Marc Ramuz.

Solar battery made from carbon

'Creating silicon solar cells requires a lot of steps,' Vosgueritchian explained. 'But our entire device can be built using simple paint methods that don't require expensive tools and machines.'

The solar cell tested by the Zhenan team consists of a photovoltaic layer, which absorbs sunlight, sandwiched between two electrodes. In a typical thin solar panel, the electrodes are made of conductive metals and Indium - Tin oxides (ITO).'Materials such as indium are rare and become more expensive as demand for solar cells, touch screen panels and other electronic devices increases , ' Bao said. 'Carbon, on the other hand, is low cost and very rich on Earth'.

The solar cell, made entirely of carbon from the research team, consists of a photovoltaic layer, which absorbs sunlight, sandwiched between two electrodes.

In this study, Bao and her colleagues replaced silver and ITO used in conventional electrodes with graphene - carbon sheets are a thick atom - and single-walled carbon nanotubes are 10,000 times thinner than hair fibers.'Carbon nanotubes have electrical conductivity and strong light absorption ability , ' Bao said.

Scientists used substances made from carbon nanotubes and 'buckyballs' to act as layers. Buckyballs are football-shaped carbon molecules, about one nanometer in diameter (nm). The team recently applied for patents for the entire device.

"All of our solar cell components, from top to bottom, are made of carbon materials , " Vosgueritchian said. 'Other research groups have reported carbon solar cells, but in fact those batteries have only the active layer in the middle that is made of carbon, and the electrodes are not.'

One drawback of the prototype made entirely of carbon is that it primarily absorbs the wavelength of near infrared light. The researchers hope that with better materials and processing techniques, the light absorption efficiency of these test samples will be significantly increased.

Stanford University's team is considering a series of ways to improve efficiency.'Surface roughness can shorten devices and make it difficult to pick up current,' Bao said. 'We have to find a way to make each layer smooth by stacking really good nano materials'.

The researchers also experimented with carbon nanomaterials that could absorb more light in a wider wave range, including the visible spectrum.

"Materials made of carbon are very strong," Bao said. "They remain stable at air temperatures of nearly 1,100 degrees Fahrenheit."

According to Vosgueritchian, the ability of carbon solar cells in addition to making conventional devices, in extreme conditions, can be even more efficient. " We believe that all carbon solar cells can be used in harsh environments, such as at high temperatures or high physical pressures ," he said. "But we want the highest efficiency available. and we are working to improve our equipment ".

"Photovoltaics will certainly be a very important source of energy that we will exploit in the future , " Bao said. "We have a lot of sunlight. We have found several ways to use this natural resource."

Other authors of this study are Wei Peng of Stanford University and Chenggong Wang and Yongli Gao, Rochester University's Department of Physics and Astronomy. The study was funded by Stanford University's Global Climate and Energy Project (Global Climate and Energy Project) and the Air Force Office for Scientific Research.