LED - a replacement for traditional light sources
White light organic light emitting diodes are considered an alternative source of traditional white light sources. They are highly efficient solid-state light sources, and electro-optical conversion efficiency has surpassed that of incandescent lamps. Recently, great progress has been made in the structure of devices and the synthesis of new materials.
The world consumes a huge amount of electricity every year. In all electrical energy consumption, lighting energy accounts for 20% of total electrical energy production. Fluorescent and incandescent lamps are the most common traditional lighting sources, and 40% of the electrical energy used for lighting is consumed by them. Incandescent lamps turn 90% of electrical energy into heat. Fluorescent lamps perform better. They convert 70% of the energy consumed into light. The typical luminous efficiencies of incandescent and fluorescent lamps are 13-20 lm/W and 90 lm/W, respectively. So in order to save energy in the world, one way is to find a replacement for traditional light sources.
Researchers have spent more than a decade researching semiconductor light-emitting diodes with better performance. Light-emitting diodes of red, green, blue and other colors made of inorganic materials have long appeared in the market, and they are widely used in traffic lights, automobile taillights and other small applications. Inorganic white light-emitting diodes have also appeared on the market, but their prices are relatively high compared to ordinary lighting applications. Now a new competitor of lighting sources has come to the market, which is based on organic semiconductor materials.
OLED shows strong competitiveness in display technology
In the past decade, OLEDs have shown strong competitiveness in terms of display technology compared to liquid crystals. Since the discovery of efficient electroluminescence in tris (8-hydroxyquinoline) aluminium (Alq3) [2] in 1987 and poly(p-phenylene vinylene) (PPV) [3] in 1990, OLED has become the most attractive. Display technology. It has the advantages of simple preparation, short response time, high brightness, wide viewing angle, low driving voltage, most likely to be applied to flexible substrates and full color display. O- LED displays are durable, efficient, and can be fabricated onto flexible substrates, such as plastic and paper surfaces, and the resulting display can be bent or rolled up. Unlike liquid crystals, OLEDs are self-illuminating and do not require backlighting, which makes OLED displays thinner and lighter.
An OLED is a multilayer film device consisting of an active charge transport layer sandwiched between two film electrodes and a light-emitting layer, at least one of which is transparent. In general, indium tin oxide (ITO) with a high work function (~4.8eV), low sheet resistance (~20 Ω / □) and transparent to visible light is used as the anode, and the cathode generally uses a low work function metal. For example, Ca, Ma, Al or their alloys Ma: Ag, Li: Al. An organic layer having good electron transport properties and hole blocking properties is placed between the cathode and the light-emitting layer.
Likewise, a hole transport layer and an electron blocking layer are used between the anode and the light-emitting layer. When the external is biased, electrons and holes are injected from the cathode and anode of the OLED, respectively. Under the action of an external electric field, electrons and holes migrate in opposite directions, and excitons are formed in the light-emitting region, and the exciton decays to radiate light outward. The migration dynamics and properties of excitons are not discussed here.
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