Chapter 4
OPV with a Crystalline Organic Pigment
Active Layer Up to 10 µm
Toshihiko Kaji
4.1 Introduction: Optical Design of Thickness of OPV
and Its Photoelectric Conversion Layer
The photoelectric conversion efficiency of OPVs has reported greatly exceeded 10%
in recent years, gradually approaching to a practical level of the solar cell performances [1–4]. It is expected that it can be manufactured with lightweight and flexible
plastic substrates and that it has a low environmental impact. Since the invention of
OPV for heterojunction and bulk heterojunction layers, various approaches such as
material design and screening [1, 5, 6], thin-film growth process [7, 8], and new
device structure [9, 10] have been developed to improve OPV photoelectric conversion efficiency. The optimization process often involves trade-offs between key cell
designs such as active layer composition and thickness. For example, the light absorption of the active layer, that is, the photoelectric conversion layer, can be increased
by increasing the film thickness of the layer, but beyond a certain thickness, the
recombination of the photogenerated charges through the active layers suppresses
the charge carrier transports and photocurrent generation.
Therefore, in order to increase the photocurrent at zero bias, that is, the shortcircuit current J sc , the thickness of the active layer has been designed in the certain
optimal range where the photocurrent generation is not limited by charge recombination and transport [11, 12]. For example, in an OPV in which an organic pigment
is vacuum-deposited, the 40-60-nm-thick active layer is typically used to absorb the
first standing wave [11, 13–15]. The second and third standing waves can be used
to further enhance absorption; thus, in the design of tandem OPVs, the bottom cell
The original version of this chapter was revised: Figure 4.6 (b) have been updated with new Figure.
The correction to this chapter is available at https://doi.org/10.1007/978-981-15-9113-6_11
T. Kaji (B)
Department of Applied Physics, Tokyo University of Agriculture and Technology, 2-24-16
Nakacho, Tokyo, Koganei 184-8588, Japan
e-mail: kaji-t@cc.tuat.ac.jp
© Springer Nature Singapore Pte Ltd. 2021, corrected publication 2021
M. Hiramoto and S. Izawa (eds.), Organic Solar Cells,
https://doi.org/10.1007/978-981-15-9113-6_4
75
OPV with a Crystalline Organic Pigment
Active Layer Up to 10 µm
Toshihiko Kaji
4.1 Introduction: Optical Design of Thickness of OPV
and Its Photoelectric Conversion Layer
The photoelectric conversion efficiency of OPVs has reported greatly exceeded 10%
in recent years, gradually approaching to a practical level of the solar cell performances [1–4]. It is expected that it can be manufactured with lightweight and flexible
plastic substrates and that it has a low environmental impact. Since the invention of
OPV for heterojunction and bulk heterojunction layers, various approaches such as
material design and screening [1, 5, 6], thin-film growth process [7, 8], and new
device structure [9, 10] have been developed to improve OPV photoelectric conversion efficiency. The optimization process often involves trade-offs between key cell
designs such as active layer composition and thickness. For example, the light absorption of the active layer, that is, the photoelectric conversion layer, can be increased
by increasing the film thickness of the layer, but beyond a certain thickness, the
recombination of the photogenerated charges through the active layers suppresses
the charge carrier transports and photocurrent generation.
Therefore, in order to increase the photocurrent at zero bias, that is, the shortcircuit current J sc , the thickness of the active layer has been designed in the certain
optimal range where the photocurrent generation is not limited by charge recombination and transport [11, 12]. For example, in an OPV in which an organic pigment
is vacuum-deposited, the 40-60-nm-thick active layer is typically used to absorb the
first standing wave [11, 13–15]. The second and third standing waves can be used
to further enhance absorption; thus, in the design of tandem OPVs, the bottom cell
The original version of this chapter was revised: Figure 4.6 (b) have been updated with new Figure.
The correction to this chapter is available at https://doi.org/10.1007/978-981-15-9113-6_11
T. Kaji (B)
Department of Applied Physics, Tokyo University of Agriculture and Technology, 2-24-16
Nakacho, Tokyo, Koganei 184-8588, Japan
e-mail: kaji-t@cc.tuat.ac.jp
© Springer Nature Singapore Pte Ltd. 2021, corrected publication 2021
M. Hiramoto and S. Izawa (eds.), Organic Solar Cells,
https://doi.org/10.1007/978-981-15-9113-6_4
75