Siemens has partnered with the Universities of Linz and Karlsruhe (TH) to produce organic photodiodes that are very sensitive to infrared radiation with wavelengths of more than one micrometer (µm).
The detectors can be used in gas sensors, night vision systems, and cancer diagnostics. When used in these applications, organic photodiodes with semiconductor nanocrystals could result in substantial cost savings.
Organic photodiodes mostly detect visible light, but they are also efficient detectors of infrared radiation with a wavelength of not more than 1 µm. But with this recent breakthrough the researchers were able to produce the diodes using quantum dots (semiconductor crystals) consisting of about 50 atoms to expand the range to 2 µm.
Conventional photodiodes made of silicon are not sensitive to radiation with wavelengths of more than 1.1 m m. The new organic photodiodes are based on plastics, making the production of large surface areas diodes much cheaper than the more costly gallium arsenide semiconductors used today.
A solution containing the plastics is applied to a substrate. The solution contains semiconducting polymers and fullerenes, which take on the roles of the electron donors and acceptors of the semiconductor.
Using their method of imbedding quantum dots in organic diodes, they have achieved service life periods of at least one year. The measurements also indicate extremely high quantum efficiencies, which means the diodes convert the incident light into electric current with a high degree of efficiency. With a 256 x 256 pixel image sensor, the researchers show that the technology can even be used on an active-matrix circuit, demonstrating for the first time that solution-based semiconductor nanocrystals are suitable for industrial imaging technology.
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