Friday, 21 Sep 2018

Solution-processed organic tandem solar cells achieves 17.3% efficiency

Recent research suggests organic solar cells could be as efficient as those based on inorganic materials such as silicon and perovskites

14 Aug 2018 | Editor

Researchers from Nankai University in China have announced they have determined which photoactive material combinations are best for making "tandem" organic photovoltaic devices. Test cells made in the laboratory the researchers' were able to reach power conversion efficiencies (PCEs) of 17.3%, a value that is significantly higher than the current 14 to 15%. The researchers believe through further optimisation PCEs approaching 25% could be possible for organic photovoltaic devices.

The team of researchers led by Professor Yongsheng Chen of Nankai University developed a semi-empirical model to predict which materials work best together in tandem cells. The model suggested a new electron-grabbing material called O6T-4F, which works better at infrared energies. The researchers then used their model to pair a layer containing that material with one that had well matched electrical properties and could absorb visible light. That second layer used a relatively new electron acceptor, called F-M for short, the researchers had previously developed.

According to the researchers organic photovoltaics (OPVs) show much promise for next-generation solar cells mainly due to their potential to be manufactured are "low" cost, can be manufactured on flexible substrates, and "printed" over large areas.

Further, a number of researchers around the world have succeeded in improving the PCE of these cells from around 5% to 14-15% over the last decade primarily using tandem cell structures in which photoactive layers with complementary light absorption characteristics are stacked on top of each other.

A key design benefit of tandem cells is they have cells that absorb over a wider range of sunlight wavelengths than single materials. This is because the photoactive organic materials in each "sub-cell" can be designed with different but matching energy bandgaps.

The researchers added, although 14-15% is impressive, this value lags behind that of photovoltaic platforms based on inorganic materials, which for their part boast PCEs of between 18 to 22%. One of the main reasons for the relatively low PCE of OPVs is the limited sunlight absorption range of materials used to make the rear subcell in the devices. Indeed, most of these materials can only absorb photons with energies of around 1.3 eV (90 nm), which means they miss a large part of the solar spectrum.

The team, which includes researchers from the National Center for Nanoscience and Technology in Beijing and South China University of Technology in Guangzhou says that they are already looking for even better material combinations for making OPV tandem solar cells and improving their stability.

"We screened for the most efficient photoactive materials and then found the optimal match for both the front and rear subcells in these devices"

"Our analyses are based on previous theoretical works and state-of-the-art experimental results."

"Thanks to our calculations, we were able to make solution-processed two-terminal monolithic tandem OPV cells with a remarkable new record PCE of 17.3%."

"According to our analyses, the OPV of 17.3% could be increased further to 25% and these materials could be as good as other solar technologies, OPVs thus show great potential for commercial applications."

"We found that while the initial stability tests show that the devices are stable and degrade by only 4% after 166 days, their long-term stability needs further testing and optimization."

Professor Yongsheng Chen, Nanaki University

Organic and solution-processed tandem solar cells with 17.3% efficiency

Lingxian Meng | Yamin Zhang | Xiangjian Wan | Chenxi Li | Xin Zhang | Yanbo Wang | Xin Ke | Zuo Xiao | Liming Ding | Ruoxi Xia | Hin-Lap Yip | Yong Cao | Yongsheng Chen

  • State Key Laboratory and Institute of Elemento-Organic Chemistry, Centre of Nanoscale Science and Technology and Key Laboratory of Functional Polymer Materials, College of Chemistry, Nankai University, Tianjin, 300071, China
  • Center for Excellence in Nanoscience (CAS), Key Laboratory of Nano system and Hierarchical Fabrication (CAS), National Center for Nanoscience and Technology, Beijing 100190, China.
  • Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, Guangzhou, 510640, China

Science 09 Aug 2018: | eaat2612 | DOI: 10.1126/science.aat2612


Though organic photovoltaic cells (OPVs) have many advantages, their performance still lags far behind that of other photovoltaic platforms. One of the most fundamental reasons for this is the low charge mobility of organic materials, leading to a limit on the active layer thickness and efficient light absorption. In this work, guided by a semi-empirical model analysis and using the tandem cell strategy to overcome such issues, and taking advantage of the high diversity and easily tunable band structure of organic materials, a record and certified 17.29% power conversion efficiency for a 2-terminal monolithic solution processed tandem OPV is achieved.


#opv, #solar
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