Hole Transport Materials (HTM)

The organic light-emitting diode (OLED) material is a complete device composed of an anode, a cathode and an organic functional layer. The anode of an OLED is usually composed of indium tin oxide (ITO), which is highly transparent, has good conductivity, and has a high work function. The cathode of an OLED is often composed of metals such as calcium, magnesium, aluminum, and silver that are highly reflective and have a low work function. The organic functional layers of OLEDs are composed of multiple organic layers with different functions such as carrier injection and carrier transport. Hole transport material (HTM) is an organic semiconductor material that can realize the directional and orderly and controllable migration of holes under the action of an electric field to achieve the function of transporting charges. The performance of HTM determines the ability of the device to capture and transport holes. On the one hand, HTM blocks electrons in the light-emitting layer to a certain extent, improves the recombination probability of electrons and holes, and enhances the luminous efficiency of the device. On the other hand, HTM can also reduce the energy barrier of holes in the injection process, and improve the efficiency of hole injection, thereby improving the brightness, efficiency and lifetime of the device. HTM mainly includes polyparaphenylene vinylene (PPv), polythiophene, polysilane, triphenylmethane, triarylamine, hydrazone, pyrazoline, carbazole, butadiene, etc.

Figure 1. HTM in OLED device structure

Applications:

Organic photoelectric conversion device: HTM is an important part of organic photoelectric conversion devices, which can be applied to the preparation and production of electroluminescent devices, organic light guide devices, etc. Organic electroluminescent devices are low-voltage, high-current injection light-emitting devices, which are called organic light-emitting diodes (OLEDs). For organic electroluminescent hole transport materials, HTM can effectively improve hole transport efficiency. At the same time, it can form a uniform amorphous film without pinholes, has good thermal stability, increases the photoelectric conversion efficiency of the device, expands the application field of the device, and can prepare the OLED device into a large area, strong flexibility, and ultra-thin dispalys. For organic light guide devices, HTM endows organic light guide devices with good electrostatic characteristics and photosensitivity.

Reference

Ramanaskanda Braveenth, Hyeong Bae, Quynh Nguyen, Haye Ko, Choong Lee, Hyeong Kim, Jang Kwon, Kyu Chai. Spirobifluorene Core-Based Novel Hole Transporting Materials for Red Phosphorescence OLEDs [J]. Molecules, 2017, 22(3), 464.

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