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Sublimed Materials

Sublimed material is a kind of substance that can be used to modify organic semiconductor materials. Organic semiconductor materials, with advantages of low toxicity, low price and simple preparation process, have been widely used in the fields of photoelectric and electrical products, such as conduction, organic luminescence, solar cells, field effect transistors, electrochromic and electrochemical cells. However, due to some drawbacks, the application of organic semiconductor materials is limited. Co-sublimation-controlled doping is a necessary means to improve the properties of organic semiconductor materials, and sublimed materials play a key role in the modification process. By the means of charge transfer, co-sublimation-controlled doping integrates a number of one or more donor or acceptor molecules with organic semiconductor materials, forming a stable community of properties and components. Generally, oxidation reaction is equivalent to p-type doping, while reduction reaction is equivalent to n-type doping. The co-sublimation-controlled doping modification method has the following characteristics. First, the doping layer has good thermal stability at 80-150oC. Second, stable multilayer doped and undoped layer structure can be achieved. Co-sublimation-controlled doping equipment is shown in figure 1.

Sublimed MaterialsFigure 1 The co-sublimation-controlled doping equipment.

Applications:

  • Organic photovoltaic cell: As for organic photovoltaic cells, sublimed materials are applied to improve the solar energy conversion efficiency. By co-sublimation-controlled doping, a layer of F4-TCNQ doped zinc phthalocyanine (ZnPc) or vanadium phthalocyanine (VOPc) is added between ITO and imide. When this material is illuminated by light, the series resistance decreases and the performance of doped devices is significantly improved.
  • Organic light-emitting device: Organic light-emitting is a phenomenon in which energy is absorbed by an organic semiconductor in a certain way without heat and the energy is directly converted into radiation. It is the base of double carrier injection doped luminescence of metal/polymer/metal-structured polymer light-emitting diodes. F4-TCNQ is doped vanadium phthalocyanine (VOPc) by the means of co-sublimation-controlled doping, which can be used as the charge transport layer of OLEDs. The performance of the obtained devices is improved due to the increase in bulk conductivity of the hole transport layer.

Sublimed MaterialsFigure 2 Layout of the designed OLED.

Classification:

Not only organic crystals but amorphous organic semiconductor materials with large bandwidth and small energy gap can also adopt co-sublimation-controlled doping method. Because the electron transmission capacity of organic optoelectronic materials is far lower than that of holes, the high optical voltage and high optical current in organic optoelectronic devices are often realized through n-type doping. Compared with p-type doping, n-type doping plays a more important role. Therefore, the sublimed materials can be divided into p-type sublimed materials and n-type sublimed materials.

  • p-type sublimed materials: P-type sublimed materials are electron acceptor and the typical representatives are F4-TCNQ and DDQ.

Sublimed MaterialsFigure 3 The molecular structure of p-type sublimed materials.

  • n-type sublimed materials: N-type sublimed materials are electron donor, and the typical representatives are BEDT-TTF, Coumarin 6, Rhodamine B and QAD.

Sublimed MaterialsFigure 4 The molecular structure of n-type sublimed materials.

References:

  1. Pfeiffer M, Beyer A, Plnnigs B, et al. Controlled p-doping of pigment layers by cosublimation: Basic mechanisms and implications for their use in organic photovoltaic cells[J]. Solar Energy Materials and Solar Cells, 2000, 63(1):83-99.
  2. Blochwitz J, Pfeiffer M, Fritz T, et al. Low voltage organic light emitting diodes featuring doped phthalocyanine as hole transport material[J]. Applied Physics Letters, 1998, 73(6):729-731.

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