By Simon Aughton,
Scientists at a Canadian university have created the first ‘wet’ semiconductor device capable of outperforming conventional silicon chips, by ‘painting’ it onto glass.
The University of Toronto (UofT) team cooked up semiconductor particles just a few nanometres across in a flask containing extra-pure oleic acid, the main ingredient in olive oil. The researchers then placed a drop of solution on a glass slide patterned with gold electrodes and forced the drop to spread out into a smooth, continuous semiconductor film using the spin-coating process.
They then dipped the film into methanol for two hours; once the solvent evaporated, it left an 800nm-thick layer of the light-sensitive nanoparticles.
Gold electrodes are attached to the film and the chip is exposed to infrared light. The nanoparticles absorb the light, allowing current to flow between the electrodes. The amount of current can be varied by altering the strength of the infrared beam.
‘The key to our success was controlled engineering at the nanometre lengthscale: tailoring colloidal nanocrystal size and surfaces to achieve exceptional device performance,’ said Gerasimos Konstantatos, a doctoral researcher at UofT. ‘With this finding, we now know that simple, convenient, low-cost wet chemistry can produce devices with performance that is superior compared to that of conventional grown-crystal devices.’
The researchers observed that at room temperature, the paint-on photodetectors were about ten times more sensitive to infrared than the sensors that are currently used in military night-vision and biomedical imaging.
‘These are exquisitely sensitive detectors of light,’ said professor Ted Sargent, who led the team. ‘It’s now clear that solution-processed electronics can combine outstanding performance with low cost.’