Dielectric Materials for Electrical Engineering

Chapter 20

Semiconducting Organic Materials for Electroluminescent Devices and Photovoltaic Conversion 1

20.1. Brief history

During the last 50 years, polymers have held an increasingly important place amongst dielectric materials. They are light, easy to process, and their physico-chemical properties can be modified by well-established techniques of organic chemistry. Although less present in industrial applications, semiconducting organic materials offer the same advantages as their inorganic counterparts. The strong interest aroused by organic electronics since the end of the 1980s recently led to the commercialization of organic displays. Nevertheless, more work needs to be put into research, particularly to achieve the production of flat screens and to improve the performances of organic photovoltaic cells. The organic semiconductors which constitute the active layers of these components are generally listed in two categories: polymers and materials with low molar mass, or “small molecules”.

The phrase “organic semiconductor”, applied today to different types of materials, was initially applied only to certain molecular crystals (naphthalene, anthracene, etc.) presenting properties similar to inorganic semiconductors. In particular, the electroluminescence of anthracene was studied from the beginning of the 1960s onwards [POP 63]. However, the functioning voltages required, higher than 100 V, and the weak quantum efficiency (less than 0.1%) of the devices did not allow commercial ...