| Work Detail |
Tetracene is a polycyclic aromatic hydrocarbon that is commonly used in organic field-effect transistors (OFETs), organic light-emitting diodes (OLEDs), or as a sensitizer in chemoluminescence. Singlet fission solar cells can produce two electrons from one photon, making the cell more efficient
Researchers from the US Department of Energys National Renewable Energy Laboratory (NREL) are planning to use synthesized tetracene diacid (Tc-DA) to develop so-called singlet fission solar cells. Tetracene is a polycyclic aromatic hydrocarbon that is commonly used in organic field-effect transistors (OFETs), organic light-emitting diodes (OLEDs), or as a sensitizer in chemoluminescence.
Singlet exciton fission is an effect seen in certain materials whereby a single photon can generate two electron-hole pairs as it is absorbed into a solar cell rather than the usual one. The effect has been observed by scientists as far back as the 1970s and though it has become an important area of research for some of the world’s leading institutes over the past decade, translating the effect into a viable solar cell has proved complex.
Singlet fission solar cells can produce two electrons from one photon, making the cell more efficient. This happens through a quantum mechanical process where one singlet exciton (an electron-hole pair) is split into two triplet excitons. According to the researchers, acenes have the potential to display improved quantum yields in this process.
In the study “Tetracene diacid aggregates for directing energy flow toward triplet pairs,” published in the Journal of the American Chemical Society, the scientists explained that Tc-DA exploits intermolecular hydrogen-bonding interactions at semiconductor surfaces to well-ordered monolayers. “However, we found that we could control the aggregation of Tc-DA as it approached the surface through solvent and concentration choices,” said NREL researcher Nicholas Pompetti. “This opened up insights about tetracene-based aggregates and how their size and structure provide promising pathways for their use in light-harvesting applications.”
The team concluded that tetracene and its derivatives are prime candidates for singlet fission (SF) after analyzing their aggregate structures via nuclear magnetic resonance (NMR) spectroscopy and computational modeling. “The excited-state dynamics were surprisingly sensitive to crossing a well-defined threshold of concentration, almost like going through a phase transition for a pure material,” said research co-author Justin Johnson.
The group also found that some noncovalent tetracene-based aggregates, which were stabilized at certain solvent polarities and concentrations, were able to form charge transfer and multi-excitonic states, which they described as “desirable species for delivering charges to an electrode or catalyst.”
“Nature uses hydrogen bonds in many types of aggregated architectures to tune energy landscapes in a similar fashion, like funneling water to a reservoir,” Johnson said. “Bringing such principles to artificial light-harvesting systems with the potential for controlling multiexcitons is a logical pursuit that is leading to interesting consequences.”
The research on singlet fission has led to other interesting discoveries in recent times.
Last year, researchers from the Massachusetts Institute of Technology (MIT) and the University of Virginia announced plans to use acenes, which are benzene molecules with unique optoelectronic properties, in singlet fission solar cells. Their approach consisted of adding carbodicarbenes ligands to acenes that were already doped with boron and nitrogen.
In 2019, an MIT research group demonstrated how singlet exciton fission could be applied to silicon solar cells and could lead to cell efficiencies as high as 35%. They claimed to be the first group to transfer the effect from one of the ‘excitonic’ materials known to exhibit it, in that case also tetracene. They achieved the feat by placing an additional layer just a few atoms thick of hafnium oxynitride between the silicon solar cell and the excitonic tetracene layer.
The MIT researchers described their work as “turbocharging” silicon solar cells and said it differs from the most common approaches to increasing solar cell efficiencies, which these days are focused more on tandem cell concepts. “We’re adding more current into the silicon as opposed to making two cells,” they stated at the time. |
