Chapter 9
Parts-Per-Million-Level Doping Effects
and Organic Solar Cells Having
Doping-Based Junctions
Masahiro Hiramoto
9.1 Introduction
9.1.1 Motivation
Controlling the p- and n-type behavior, i.e., whether holes or electrons are responsible
for electric conduction, respectively, by adding an extremely small quantity of impurity (doping) has been a central part of inorganic semiconductor electronics since
the 20th century, such as silicon integrated circuits, solar cells, and light-emitting
diodes. However, the genuine potential of organic semiconductors (OSCs) has been
obscured for a long time by external contaminants such as oxygen. We strongly
believe that the p- and n-type behavior of OSCs should be controlled by parts-permillion (ppm)-level doping, similar to inorganic semiconductors such as silicon. We
expect that veiled physical properties unique to OSCs would be found during such
studies to achieve conduction-type control of OSCs by ppm doping.
We propose that the points described below are essential to developing the
principles underlying the doping of OSCs.
(i) A ppm-doping strategy should be performed on sub-ppm purified OSCs
together with the total removal of oxygen from the air, which acts as an external
dopant.
(ii) Perfect pn-control, namely, any single or blended OSC should exhibit either n
or p-type behavior only by impurity doping.
(iii) To precisely clarify the nature of the doping effects, ppm doping in the bulk of
OSC single crystals with few grain boundaries should be performed.
M. Hiramoto (B)
National Institutes of Natural Sciences, Institute for Molecular Science, 5-1 Higashiyama,
Myodaiji, Okazaki 444-8787, Aichi, Japan
e-mail: hiramoto@ims.ac.jp
© Springer Nature Singapore Pte Ltd. 2021
M. Hiramoto and S. Izawa (eds.), Organic Solar Cells,
https://doi.org/10.1007/978-981-15-9113-6_9
217
Parts-Per-Million-Level Doping Effects
and Organic Solar Cells Having
Doping-Based Junctions
Masahiro Hiramoto
9.1 Introduction
9.1.1 Motivation
Controlling the p- and n-type behavior, i.e., whether holes or electrons are responsible
for electric conduction, respectively, by adding an extremely small quantity of impurity (doping) has been a central part of inorganic semiconductor electronics since
the 20th century, such as silicon integrated circuits, solar cells, and light-emitting
diodes. However, the genuine potential of organic semiconductors (OSCs) has been
obscured for a long time by external contaminants such as oxygen. We strongly
believe that the p- and n-type behavior of OSCs should be controlled by parts-permillion (ppm)-level doping, similar to inorganic semiconductors such as silicon. We
expect that veiled physical properties unique to OSCs would be found during such
studies to achieve conduction-type control of OSCs by ppm doping.
We propose that the points described below are essential to developing the
principles underlying the doping of OSCs.
(i) A ppm-doping strategy should be performed on sub-ppm purified OSCs
together with the total removal of oxygen from the air, which acts as an external
dopant.
(ii) Perfect pn-control, namely, any single or blended OSC should exhibit either n
or p-type behavior only by impurity doping.
(iii) To precisely clarify the nature of the doping effects, ppm doping in the bulk of
OSC single crystals with few grain boundaries should be performed.
M. Hiramoto (B)
National Institutes of Natural Sciences, Institute for Molecular Science, 5-1 Higashiyama,
Myodaiji, Okazaki 444-8787, Aichi, Japan
e-mail: hiramoto@ims.ac.jp
© Springer Nature Singapore Pte Ltd. 2021
M. Hiramoto and S. Izawa (eds.), Organic Solar Cells,
https://doi.org/10.1007/978-981-15-9113-6_9
217