Chapter 10
Proposal for Future Organic Solar Cells
Masahiro Hiramoto
Recent driving forces for increases in efficiency of organic solar cells have relied on
the numerous repeats of the circulation around the syntheses of new organic semiconductors, blends, and performance checks. However, neglect of physical principles,
which are hidden in the back of the complicated systems, should be prevented for
future long-range development of organic solar cells. In Chapter 10, therefore, the
proposals for future organic solar cells are discussed based on the unconventional
considerations and the fundamental physical aspects.
10.1 Is Blended Junction Necessary?
The primary question, why a blended junction was inevitably introduced, directly
offers the alternative methods for constructing organic solar cells. The first answer is
the necessity of combining donor and acceptor molecules to dissociate excitons. A
logical consequence is exciton dissociation without combining donor and acceptor
molecules, i.e., the use of a single organic semiconductor. The second answer is an
extremely short exciton diffusion length of approximately 10 nm. A logical consequence is the use of a material with a long exciton diffusion length. The third answer
is the very small relative dielectric constant (ε) of about 3 of organic semiconductors,
which inhibits exciton dissociation. A logical consequence is the use of the material
with large ε.
M. Hiramoto (B)
National Institutes of Natural Sciences, Institute for Molecular Science, 5-1 Higashiyama,
Myodaiji, Okazaki, Aichi 444-8787, 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_10
255
Proposal for Future Organic Solar Cells
Masahiro Hiramoto
Recent driving forces for increases in efficiency of organic solar cells have relied on
the numerous repeats of the circulation around the syntheses of new organic semiconductors, blends, and performance checks. However, neglect of physical principles,
which are hidden in the back of the complicated systems, should be prevented for
future long-range development of organic solar cells. In Chapter 10, therefore, the
proposals for future organic solar cells are discussed based on the unconventional
considerations and the fundamental physical aspects.
10.1 Is Blended Junction Necessary?
The primary question, why a blended junction was inevitably introduced, directly
offers the alternative methods for constructing organic solar cells. The first answer is
the necessity of combining donor and acceptor molecules to dissociate excitons. A
logical consequence is exciton dissociation without combining donor and acceptor
molecules, i.e., the use of a single organic semiconductor. The second answer is an
extremely short exciton diffusion length of approximately 10 nm. A logical consequence is the use of a material with a long exciton diffusion length. The third answer
is the very small relative dielectric constant (ε) of about 3 of organic semiconductors,
which inhibits exciton dissociation. A logical consequence is the use of the material
with large ε.
M. Hiramoto (B)
National Institutes of Natural Sciences, Institute for Molecular Science, 5-1 Higashiyama,
Myodaiji, Okazaki, Aichi 444-8787, 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_10
255