Chapter 18
Organic Semiconductors
Abstract An introduction to organic semiconductors, based on the sp
2 bonding scheme is given,
covering small organic molecules and polymers. Their electronic structure, doping schemes, as well
as their particular transport and optical properties are covered.
18.1 Introduction
Organic semiconductors are based on carbon compounds. The main structural difference from inorganic
semiconductors is the bond based on sp
2 hybridization (cf. Sect. 2.2.3) as present in benzene (and
graphite). Diamond, although consisting of 100% carbon, is not considered an organic semiconductor.
We note that carbon can form further interesting structures based on sp
2 bonds, such as carbon nanotubes
(Sect. 14.3), (single or few layer) graphene sheets (Sect. 13.1) rolled up to form cylinders, or fullerenes,
e.g. soccer-ball-like molecules such as C 60 .
In the 1980 Handbook on Semiconductors only a good ten pages were devoted to organic semiconductors [1553]. Now several textbooks are available [1554, 1555] for a much more detailed treatment
than given here.
18.2 Materials
18.2.1 Small Organic Molecules, Polymers
The prototype organic molecule is the benzene molecule with its ring-like structure (Fig. 2.8).
There is a large number of organic, semiconducting molecules that differs by the number of benzene
rings (Fig. 18.1), the substitution of carbon atoms by nitrogen or sulfur (Fig. 18.2a, b), the polymerization (Fig. 18.2c) or the substitution of hydrogen atoms by side groups (Fig. 18.2d). Since PPV is
insoluble, typically derivatives such as MEH-PPV
1 [1557] that are soluble in organic solvents are used.
Compared to benzene, the substitution of one carbon atom by nitrogen (pyridine) represents doping
with one electron. In Fig. 18.3, the most important building blocks of organic molecules are shown.
1 2-ethoxy,5-(2’-ethyl-hexyloxy)-1,4-phenylene vinylene.
© Springer Nature Switzerland AG 2021
M. Grundmann, The Physics of Semiconductors, Graduate Texts in Physics,
https://doi.org/10.1007/978-3-030-51569-0_18
473
Organic Semiconductors
Abstract An introduction to organic semiconductors, based on the sp
2 bonding scheme is given,
covering small organic molecules and polymers. Their electronic structure, doping schemes, as well
as their particular transport and optical properties are covered.
18.1 Introduction
Organic semiconductors are based on carbon compounds. The main structural difference from inorganic
semiconductors is the bond based on sp
2 hybridization (cf. Sect. 2.2.3) as present in benzene (and
graphite). Diamond, although consisting of 100% carbon, is not considered an organic semiconductor.
We note that carbon can form further interesting structures based on sp
2 bonds, such as carbon nanotubes
(Sect. 14.3), (single or few layer) graphene sheets (Sect. 13.1) rolled up to form cylinders, or fullerenes,
e.g. soccer-ball-like molecules such as C 60 .
In the 1980 Handbook on Semiconductors only a good ten pages were devoted to organic semiconductors [1553]. Now several textbooks are available [1554, 1555] for a much more detailed treatment
than given here.
18.2 Materials
18.2.1 Small Organic Molecules, Polymers
The prototype organic molecule is the benzene molecule with its ring-like structure (Fig. 2.8).
There is a large number of organic, semiconducting molecules that differs by the number of benzene
rings (Fig. 18.1), the substitution of carbon atoms by nitrogen or sulfur (Fig. 18.2a, b), the polymerization (Fig. 18.2c) or the substitution of hydrogen atoms by side groups (Fig. 18.2d). Since PPV is
insoluble, typically derivatives such as MEH-PPV
1 [1557] that are soluble in organic solvents are used.
Compared to benzene, the substitution of one carbon atom by nitrogen (pyridine) represents doping
with one electron. In Fig. 18.3, the most important building blocks of organic molecules are shown.
1 2-ethoxy,5-(2’-ethyl-hexyloxy)-1,4-phenylene vinylene.
© Springer Nature Switzerland AG 2021
M. Grundmann, The Physics of Semiconductors, Graduate Texts in Physics,
https://doi.org/10.1007/978-3-030-51569-0_18
473