Light-emitting diodes (LEDs) are rapidly becoming ubiquitous, replacing incandescent and fluorescent lighting in many applications. Their high lumen output, low energy consumption and long lifetime are just three of the reasons they’ve become so dominant. Something that’s spoken about less often is that while LEDs don’t radiate heat (which is why they feel cool to the touch), they generate heat internally, at the semiconductor junction, and high temperatures here can reduce the lifetime of the LED. This is the case even for low-power LEDs, but as the demand for power increases, managing this will be a major challenge for the industry.
Now, researchers from Taiwan have developed a composite material that could offer a real alternative to today’s heavy, rigid aluminium heatsinks. In a paper from the June issue of Carbon [DOI: 10.1016/j.carbon.2016.01.097], they present a heatsink made from polyamide (PA) and reduced graphene (rGO), which they claim can effectively dissipate the heat produced within an LED lamp.
Using titanate coupling agent (TCA) as a ‘bridging molecule’ between the graphene oxide and polyamide, the team produced a dense nanocomposite that is 53% more thermally conductive than the polymer alone. To test its performance, they produced two heatsinks – one made solely from PA, and the other made from the PA/TCA-rGO composite. These were applied to two identical LED arrays, and both were analysed using thermal imaging and a series of thermocouples.
A higher equilibrium temperature was found for the PA/TCA-rGO heatsink, demonstrating a faster heat transfer rate than that achieved by the PA heatsink. Given that high temperatures within the junction have been shown to degrade the performance of LED over time, the lamp’s durability was also tested. It showed that the lamp cooled by the composite heatsink retained 95% of its light intensity, compared with 69% for that using the PA heatsink.
In reality, the team have produced a thermal dissipation material that combines the benefits of a thermoplastic – it can be injection-moulded to fit any shape – with the thermal performance of the considerably-more expensive graphite. The researchers believe that therefore, this material brings us a step closer to practical heat sinks for LEDs that are low cost, light weight, and mechanically flexible, that improve the lifetime of the device in the process.
E-C Cho, J-H Huang, C-P Li, C-W Chang-Jian, K-C Lee, Y-S Hsiao, J-H Huang, “Graphene-based thermoplastic composites and their application for LED thermal management”, Carbon 102 (2016) 66–73. DOI: 10.1016/j.carbon.2016.01.097