Indoor Light and Organic Solar Cells - Energy Without Sunlight

Image Credit: Thor Balkhed - Wuming Wang, PhD Student, and Jonas Bergqvist, Principal Research Engineer in the solar cell laboratory

The new organic solar cell, optimized to convert ambient indoor light to electricity, is being developed by scientists at Sweden's Linköping University, the Chinese Academy of Sciences, and the University of Science and Technology Beijing.

Although the power produced by it is low, the scientists believe it could be enough power to support the many products that the Internet of Things will bring online. 

Low energy consuming devices sensors that detect and measure moisture, particle concentrations, temperature, and other parameters will require small and cheap sources of renewable energy.

The researchers developed an active layer made up of donor and acceptor materials. The new combination - a non-fullerene acceptor blended with a polymer donor - supported the development of a photoactive layer allowing it to absorb the exact wavelengths of light that are typically found in most indoor environments. In a nutshell, donor materials absorb photons, while acceptors acquire electrons. Photovoltaic characterizations of the new solar cell revealed a low energy loss below 0.60 eV.

Two prototypes have been created so far, one measuring 1 square centimeter (0.2 sq in) and the other measuring 4 sq cm (0.6 sq in).

The optimized organic photovoltaic cell, with an area of 1 cm2, showed a power conversion efficiency of 26.1% with an open-circuit voltage of 1.10  V under an LED illumination of 1000 lux (2700 K).

“We are confident that the efficiency of organic solar cells will be further improved for ambient light applications in coming years, because there is still a large room for optimization of the materials used in this work,” said professor Jianhui Hou from the Chinese Academy of Sciences.

The technology is now being commercialized by a Linköping spin-off company. A paper on the research, which was led by the university's Assoc. Prof. Feng Gao, was recently published in the journal Nature Energy.

Sources: Linköping University & Newatlas

Organic Solar Cells Break New Efficiency Record: 17.3%

In recent years, scientists have been trying to find a way to improve the efficiency of organic photovoltaic cells. Some researchers have even thought that organic solar cells may never improve beyond 15 percent. Solar cells based on silicon, by comparison, are in the 18 to 22 percent range.

But in a new effort, the researchers in China have developed an organic photovoltaic cell that converts 17.3% of the energy in sunlight into electricity. 

“Organic solar cells have been studied for many years, but they’re still relatively young compared to silicon,” said Chen Yongsheng, a chemist at Nankai University in North China's Tianjin. “We still don’t understand their device performance very well.” 

Chen's group used tandem cells, which are put together by different layers of organic materials. Previous designs for tandem organic cells have failed to tap into the abundant solar energy of the near-infrared range, but Chen’s team addressed this issue. 

They used a non-fullerene acceptor molecule known as O6T-4F, which was able to work better at this wavelength. They then combined that with a layer containing a relatively new electron acceptor, called F-M for short, which the team had earlier developed. This material was shown to be an excellent match for its electrical properties and could absorb visible light.

"Different layers of the tandem cells can absorb different wavelengths of light. That means you can use sunlight in the wider wavelengths more efficiently and achieve a higher power conversion rate," Dr. Chen Yongsheng said.

"There’s no reason why an organic solar cell can’t have a similar or higher performance to silicon or perovskites,” according to Chen.

Sources:

https://physicsworld.com/a/organic-solar-cells-break-new-efficiency-record/

https://www.futuretimeline.net/blog/2018/08/15.htm

https://cen.acs.org/energy/solar-power/Organic-solar-cell-smashes-performance/96/web/2018/08

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The breakthrough is published in the journal Science

Organic Solar Cells (OSCs)

                      Organic Photovoltaic cell (Source: Fraunhofer ISE)

Organic solar cells (OSCs), also known as plastic solar cells are third-generation photovoltaic technology using organic materials (carbon-based in the form of small organic molecules, dendrimers, and polymers), to convert sunlight to electrical energy.

Organic photovoltaic devices are comprised of one or several layers including a photoactive layer between two electrode layers. These layers are printed using roll-to-roll manufacturing, similar to the way newspapers are printed, with thicknesses on the nanometer scale. Photoactive layers are typically printed on a thin plastic substrate followed by lamination with a protective and flexible foil.

In an OPV cell, sunlight is absorbed in the photoactive layers composed of donor and acceptor semiconducting organic materials (typically either polymers or small molecules), to generate photocurrents. The donor material (D) donates electrons and mainly transports holes and the acceptor material (A) withdraws electrons and mainly transports electrons.

For organic materials to become conducting or semiconducting, a high level of conjugation (alternating single and double bonds) is required.

Organic solar cells have several advantages over their traditional silicon counterparts. They are very environmentally friendly because they contain no toxic elements and can be processed at low temperature using roll-to-roll deposition, so can have an extremely low carbon footprint.

Conventional silicon solar cells are perfect for large scale electricity generation in solar farms and on the roofs of buildings, but they are not suitable for the electric vehicles and integration into windows on buildings. Organic solar cells can sit on curved surfaces, they are very lightweight, flexible and transparent.

Additionally, manufacturing cost can be reduced for organic solar cells due to their lower cost compared to silicon-based materials and the relative ease of chemical synthesis.

Disadvantages associated with organic photovoltaic cells include their low efficiency (currently ~15%) in comparison with inorganic photovoltaic devices.

Organic solar cells are new types of flexible solar cells and they will become a commercial reality very soon because it will give the designers more choice in the materials they can use.