Development of Light-Emitting Diodes

Because of their high brightness, efficiency, and long life, LEDs are rapidly replacing incandescent bulbs in many applications. Use of LEDs in traffic lights results in 50%-70% savings, primarily in bulb replacement costs. LEDs need to be changed in 5-10 years, as opposed to 1 year for conventional bulbs. In another application, the use of blue-white 

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Colloidal QDs have also been used in the development of light-emitting diodes [134, 135], by their incorporation into a thin film of conducting polymer. Moreover, colloidal QDs have also been used in the fabrication of photovoltaic devices [136, 137]. 

For on-site measurement from grab sampling, a compact optical device with disposable strips for BOD determination has been developed [36]. The system includes three pairs of light-emitting diodes and photodiodes, and the disposable strips are made of inexpensive, transparent polycarbonate plates, where Pseudomonas fluorescens is immobilized. Using the 2,6-dichlorophenol-indo-phenol sodium salt as chromophore, a linear relationship was observed between the bioluminescence of the exposed strip and the BOD value. 

The development of suitable contacts for polymer solar cells has directly profited from the developments in light-emitting diodes, due to the injec-tion/extraction similarity. Due to its lower barrier for hole transfer between most conjugated polymers and PEDOT PSS as compared to ITO, this highly doped polymer electrode was applied at an early stage in solar cells as... 

Blends of pol5miers are frequently incompatible. Consequently, compatibility problems are a concern in the field of polymeric light-emitting diodes composed from polymer blends. However, this effect is sometimes an advantage in the development of light-emitting devices. 

By 1988, a number of devices such as a MOSFET transistor had been developed by the use of poly(acetylene) (Burroughes et al. 1988), but further advances in the following decade led to field-effect transistors and, most notably, to the exploitation of electroluminescence in polymer devices, mentioned in Friend s 1994 survey but much more fully described in a later, particularly clear paper (Friend et al. 1999). The polymeric light-emitting diodes (LEDs) described here consist in essence of a polymer film between two electrodes, one of them transparent, with careful control of the interfaces between polymer and electrodes (which are coated with appropriate films). PPV is the polymer of choice. 

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