Scientists use ‘ionic liquids’ to solve one of the main challenges holding back dye-sensitized solar cells — ScienceDaily

Solar cells are fast becoming one of the main ways to generate clean electricity in many countries around the world. Over the past few decades, a large amount of effort has been devoted to making solar energy more prominent. However, the technology currently faces several challenges that limit their widespread application.

In the case of dye-sensitized solar cells (DSSCs) — a very promising photovoltaic technology — one of the main problems is dye build-up. By design, DSSCs are electrochemical systems that mimic photosynthesis in plants; they rely on special photosensitive dyes to convert sunlight into electricity. Ideally, the dye should be applied evenly over the surface of an oxide electrode behind a transparent layer so that the energy from the absorbed sunlight can be easily transferred to the electrons of the dye. This process generates free electrons that power an external circuit. However, most dyes tend to accumulate on the electrode surface in a way that impedes the desired flow of light and electrical charges. This takes a toll on the performance of DSSCs that has proven difficult to overcome.

Fortunately, a team of scientists led by Associate Professor Tomohiko Inomata of the Nagoya Institute of Technology, Japan, may have found a solution to this problem. In their latest study published in RSC Advances, they showed that certain ionic liquids (molten salts that are in a liquid state at relatively low temperatures) can suppress ink build-up to an impressive degree. Other members of this research team included Ms. Ayaka Matsunaga and Prof. Tomohiro Ozawa from Nagoya Institute of Technology and Prof. Hideki Masuda from Aichi Institute of Technology, Japan.

But how do ionic liquids achieve this feat? To shed light on the exact mechanism at play, the researchers focused on two ionic liquids with significantly different molecular sizes and two types of dyes. Both ionic liquids had a similar molecular structure that includes an anchor that binds well to the electrode (titanium dioxide, TiO2), a main polymer chain connecting this anchor to a phosphorus atom, and three additional short polymer chains extending from the phosphorus atom and away from the “vertical” main chain.

The researchers immersed TiO2 electrodes in solutions of different dye-ionic-liquid proportions and carefully analyzed how the different molecules attached to them. After optimizing the synthesis procedure, they found that DSSCs made using ionic liquid with a longer molecular structure performed remarkably better than their counterparts with unmodified oxide electrodes. “The large spatial molecular structure of ionic liquids acts as an effective antifouling agent without significantly affecting the amount of dye adsorbed on the electrode“, explains Dr. Inomata.More importantly, the introduction of larger ionic liquid improves all the photovoltaic parameters of the DSSC.”

Needless to say, improving solar cell technology could give us an edge in the fight against the ongoing energy and climate crisis. Although ionic liquids are usually expensive, the method used by the team is, in fact, cost-effective. “Simply put, the idea is to apply ionic liquids only to the required part of the device — in this case, the surface of the electrode,“says Dr. Inomata.

The team believes that widespread use of electrodes modified with ionic liquids could pave the way for highly functional yet affordable materials for solar cells and catalytic systems. Since the structure of ionic liquids can be tuned during their synthesis, they offer much-needed versatility as anti-aggregation agents.

Let’s hope these findings lead to a brighter future for DSSCs and, ultimately, the planet.

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Materials provided by Nagoya Institute of Technology. Note: Content may be edited for style and length.

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