Trace Platinum and Sri Lankan Vein Graphite Boost Dye-Sensitized Solar Cells

Dye-sensitized solar cells have long promised cheap, flexible solar power, but one stubborn component has kept their price tag higher than it needs to be: the counter electrode, which is usually coated with a full layer of platinum. A research team led by M. A. K. L. Dissanayake of the National Institute of Fundamental Studies in Sri Lanka, working with colleagues at the Postgraduate Institute of Science, the Open University of Sri Lanka and Université de Limoges in France, has now reported a clever way to slash that platinum burden to a mere trace while still delivering near-platinum performance. Their secret weapon is a locally sourced, naturally occurring material that Sri Lanka happens to hold in world-class abundance: vein graphite.

The team fabricated a composite counter electrode from activated carbon, Sri Lankan natural vein graphite and a minimal quantity of platinum nanoparticles, all deposited onto a stainless-steel substrate. The choice of substrate is itself significant, because stainless steel is robust, inexpensive and compatible with roll-to-roll manufacturing, opening the door to flexible solar modules that could be produced at industrial scale. Rather than relying on a continuous platinum film, the researchers dispersed tiny amounts of platinum nanoparticles throughout a carbon matrix, letting each nanoparticle act as a catalytic hotspot while the surrounding carbon carries the electrical load.

Structural and morphological analyses confirmed that the composite came together exactly as designed. Raman spectroscopy revealed the characteristic signatures of the graphitic and disordered carbon phases, while scanning electron microscopy and energy-dispersive X-ray analysis verified that the platinum nanoparticles had been successfully incorporated into the composite layer. These characterization steps matter because the performance of a counter electrode depends critically on how well its constituents are integrated; a poorly mixed composite would leave catalytic sites stranded and electrically isolated, squandering the very platinum the design is trying to conserve.

Electrochemical testing then put the composite through its paces. Tafel polarization, cyclic voltammetry and electrochemical impedance spectroscopy all pointed in the same direction: enhanced catalytic activity and efficient charge-transfer behavior at the electrode-electrolyte interface. In a dye-sensitized solar cell, the counter electrode’s job is to catalyze the reduction of triiodide back to iodide, regenerating the redox couple that shuttles electrons through the device. A sluggish counter electrode wastes voltage and throttles current, so the strong electrochemical signatures measured here were an encouraging sign that the composite could hold its own in a working cell.

The photovoltaic results were striking. A reference device using a conventional sputtered platinum counter electrode achieved the highest efficiency in the study, 7.24 percent. The dye-sensitized solar cell built with the activated carbon/vein graphite/platinum nanoparticle composite counter electrode reached 6.87 percent, a figure that comes remarkably close to the platinum benchmark while using only a trace amount of the precious metal. For context, the unmodified activated carbon/graphite electrode without any platinum nanoparticles managed just 5.19 percent. Adding the trace platinum boosted the efficiency by a full 32 percent, transforming a mediocre carbon electrode into a serious contender.

The improvement is not simply a matter of adding more catalyst; it is a story of synergy among three very different materials. The vein graphite contributes high electrical conductivity, providing fast pathways for electrons arriving from the external circuit. The activated carbon contributes an enormous internal surface area, multiplying the number of sites where electrolyte ions can make contact with the electrode. The platinum nanoparticles contribute exceptional electrocatalytic activity toward the triiodide/iodide redox reaction, lowering the energy barrier for the regeneration reaction that keeps the cell running. Together, the three components cover each other’s weaknesses, and the whole ends up far greater than the sum of its parts.

The choice of Sri Lankan vein graphite adds an economic and geopolitical dimension to the work. Vein graphite is a rare, high-purity form of natural graphite found in commercial quantities almost exclusively in Sri Lanka, where it occurs as crystalline veins deposited in rock fissures. Its natural graphitic structure gives it excellent conductivity without the energy-intensive processing required for synthetic graphite, and sourcing it locally reduces transport costs and supply-chain risk. By building a solar cell component around a domestic natural resource, the researchers demonstrate a model of sustainable materials development that other resource-rich developing nations could emulate: rather than exporting raw ore, add value at home by engineering it into advanced energy technology.

The platinum economy of the design deserves particular attention. Platinum is among the most expensive metals on Earth, and its supply is concentrated in a handful of mining regions, making platinum-based components a vulnerability for any technology hoping to scale globally. Because the nanoparticles are so small and so few, the composite electrode captures most of platinum’s catalytic benefit at a tiny fraction of the metal loading of a sputtered film. This approach follows a broader trend in electrocatalysis research, where the goal is not to eliminate platinum entirely but to stretch it as far as physics allows, using carbon scaffolds, alloys or single-atom dispersions to maximize the catalytic turnover per gram of metal.

The study does not claim to have beaten platinum outright, and the authors are candid about that. The sputtered platinum electrode still holds the efficiency record in their own device set. What the composite offers instead is a compelling trade-off: 6.87 percent efficiency at a dramatically lower materials cost, with the added benefits of a durable stainless-steel substrate and locally sourced graphite. For applications where cost per watt matters more than squeezing out the final fraction of a percent, such as building-integrated photovoltaics, rural electrification and low-cost solar modules for emerging markets, that trade-off could be decisive.

Looking ahead, the result suggests several avenues for refinement. Optimizing the ratio of activated carbon to graphite, tuning the platinum nanoparticle loading even further downward, and exploring other low-cost substrates could push the composite closer to or beyond the platinum benchmark. The work also reinforces a lesson that resonates across modern energy research: the future of affordable solar technology may depend less on exotic new materials than on intelligent combinations of abundant ones, arranged so that every atom does the most work it can. In this case, a trace of platinum, a handful of activated carbon and Sri Lanka’s ancient vein graphite have combined to bring low-cost solar power one practical step closer.

Subject of Research: Composite counter electrodes for dye-sensitized solar cells made from activated carbon, Sri Lankan vein graphite and trace platinum nanoparticles

Article Title: Composite counter electrode for dye-sensitized solar cells engineered from trace amounts of platinum nanoparticles and Sri Lankan natural vein graphite

Article References: Dissanayake, M. A. K. L., Sandunika, P. U., Senadeera, G. K. R., Kumari, J. M. K. W., Vedraine, S., Rougier, S., Lakshan, K. L. A. C., Sewwandi, G. G. S., & Senevirathna, M. D. D. S. (2026). Composite counter electrode for dye-sensitized solar cells engineered from trace amounts of platinum nanoparticles and Sri Lankan natural vein graphite. Ionics. https://doi.org/10.1007/s11581-026-07509-9

Image Credits: AI Generated

DOI: 10.1007/s11581-026-07509-9

Keywords: dye-sensitized solar cells, counter electrode, platinum nanoparticles, vein graphite, activated carbon, Sri Lanka, electrocatalysis, photovoltaics, stainless steel substrate, charge transfer, sustainable materials, solar energy