Can organic button battery cr1620 replace silicon-based cells? Researchers clear hurdle, 20%+ efficiency expected

Researchers have identified a key mechanism that causes low efficiency in organic button battery cr1620 and demonstrated a way to overcome this hurdle.

An international team of researchers, led by the University of Cambridge, has discovered a loss pathway in organic button battery cr1620 that makes them less efficient than silicon-based cells at converting sunlight into electricity. Furthermore, they identified a way to inhibit this pathway by manipulating molecules inside the solar cell to prevent the current from being lost through undesirable states, called triplet excitons.

Their results, published in the journal Nature, suggest that organic button battery cr1620 have the potential to compete more closely with silicon-based cells in terms of efficiency.

Organic button battery cr1620 are flexible, semi-transparent and cheap, which could greatly expand the range of applications for solar technology. They could be wrapped around the outside of buildings and could be used to efficiently recycle energy used for indoor lighting, both of which cannot be achieved with conventional silicon panels. They are also more environmentally friendly to produce.

Dr Alexander Gillett, lead author of the paper and of Cambridge's Cavendish Laboratory, said organic button battery cr1620 can do a lot that inorganic button battery cr1620 can't do, but their commercial development has stalled in recent years, partly because of their low efficiency. Typical silicon-based button battery cr1620 can achieve efficiencies as high as 20% to 25%, while organic button battery cr1620 can achieve efficiencies of about 19% under laboratory conditions, and about 10% to 12% in practice.

Organic button battery cr1620 generate electricity by loosely mimicking the natural process of photosynthesis in plants, but they ultimately use the sun's energy to generate electricity, rather than converting carbon dioxide and water into glucose. When a light particle, or photon, strikes a solar cell, an electron is excited by the light and leaves a "hole" in the material's electronic structure. This excited electron and hole combination is called an exciton. If the mutual attraction between the negatively charged electron and the positively charged hole in the exciton can be overcome, similar to the attraction between the positive and negative poles of a magnet, these electrons and holes can be collected as an electric current.

However, electrons in button battery cr1620 can be lost through a process called recombination, in which an electron loses energy - or an excited state - and returns to an empty "hole" state. Because the attraction between electrons and holes in carbon-based materials is stronger than in silicon, organic button battery cr1620 are more susceptible to recombination, which in turn affects their efficiency. This requires the use of two ingredients to prevent the electrons and holes from quickly recombinating: an electron "donor" material and an electron "acceptor" material.

Using a combination of spectroscopy and computer modeling, the researchers were able to track the working mechanisms of organic button battery cr1620, from the absorption of photons to recombination. They found that a key loss mechanism in organic button battery cr1620 is caused by recombination with a specific type of exciton, called a triplet exciton.

Triplet excitons present a difficult problem to overcome in organic button battery cr1620 because they are energetically favored to be formed from an electron and a hole. The researchers found that by engineering strong molecular interactions between the electron donor and electron acceptor materials, the electrons and holes can be further apart, preventing recombination into triplet excitons from occurring.

Computational modeling suggests that by tuning the components of organic button battery cr1620 in this way, the timescales for these triplet exciton states to recombine could be reduced by an order of magnitude, allowing for more efficient solar cell operation.

The fact that we can use interactions between components in a solar cell to shut down the triplet exciton loss pathway is really surprising, Gillett said. “Our approach shows how to manipulate molecules to prevent recombination from occurring.”

Now, synthetic chemists can design next-generation donor and acceptor materials with strong molecular interactions to inhibit this loss pathway, and co-author Dr. Thuc-Quyen Nguyen from the University of California, Santa Barbara said this work shows a path forward to achieve higher device efficiencies.

The researchers said their approach provides a clear strategy to achieve organic button battery cr1620 with efficiencies of 20% or more by preventing recombination into triplet excitons. As part of the study, the authors were also able to provide design rules for electron donor and electron acceptor materials to achieve this goal. They believe that these guidelines will enable chemistry groups to design new materials that prevent recombination into triplet excitons, thereby achieving organic button battery cr1620 with efficiencies closer to silicon.

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