In recent years, alternative methods for building electronic and optoelectronic devices have been explored. Now researchers at the University of Toronto in Canada have developed ultrasensitive solution-processed quantum dot photodetectors that may be of value for many communications, imaging and monitoring applications. The devices, which they describe in the July 13 issue of Nature, offer a large device area, flexibility and convenient materials integration at low cost, compared with conventional semiconductor devices.

The investigators created photoconductive detectors by spin-coating quantum dots from a solution onto gold-interwoven electrodes. Processed from a chloroform solution, the quantum dot nanocrystals enabled easy integration with any substrate. Furthermore, their transport and trap state properties can be separately controlled via the engineering of ligands, receptor-binding compounds, and the oxidation of nanoparticle surfaces either before or after film formation.

Following the spin-coating process, the film was given a two-hour bath in methanol. After the solvent had evaporated, the scientists observed an interelectrode separation of 5 μm and a metal electrode height of 100 nm. The thickness of the light-sensitive nanoparticle layer was 800 nm.

The researchers found that the devices exhibited a photoconductive gain with increased responsivity. According to the report, the best devices demonstrated a normalized detectivity of 1.8 × 10¹³ jones (1 jones = 1 cm Hz^1/2 W^–1) at 1.3 μm at room temperature, while previous records of photoconductive detectors lie in the 10¹¹- to 10¹²-jones range.