Chapter 8
Open-Circuit Voltage in Organic Solar
Cells
Seiichiro Izawa
8.1 Introduction
Organic solar cells (OSCs) have attracted considerable attention because of their
potential advantages, which include low cost, lightweight, and environmental friendliness [1]. After more than 20 years of research, the power conversion efficiencies
(PCEs) of single-junction OSCs based on blends of electron donor (D) and acceptor
(A) semiconducting materials now exceed 17% [2]. This progress was mainly driven
by the invention of bulk heterojunction device structure at an early stage [3, 4] and
the subsequent development of low-bandgap polymer semiconductors [5]. Recently,
the development of non-fullerene acceptors has brought about a rapid increase in the
PCEs of OSCs [6].
The PCE of OSCs is lower compared to that of other SC devices: GaAs, singlecrystal silicon, and perovskite SCs have PCE values of over 25% [7]. The next
research target for OSCs is to achieve a PCE of a similar level in a highly efficient
SC device. With regard to the current generation properties, the external quantum
efficiencies (EQEs) of OSCs have already exceeded 85% [8], with internal quantum
efficiencies from absorbed photons to electrons close to 100% [9]. Further increases
in the PCE of OSCs is currently limited mainly by the open-circuit voltage (V OC ),
and to achieve additional increases in the PCE, it is therefore very important to clarify
the factors that determine V OC in OSCs, and to find a strategy for improving it.
In this chapter, we first provide the theoretical background explaining how V OC
is determined in OSCs. We then describe recent findings on how the D/A interfacial
properties largely affect V OC , and how it can be improved by controlling the nanostructure at the D/A interface. Finally, we present our conclusions and describe future
prospects for further improvement of V OC in OSCs.
S. Izawa (B)
National Institutes of Natural Science, Institute for Molecular Science, 5-1 Higashiyama
Myodaiji, Aichi, Okazaki 444-8787, Japan
e-mail: izawa@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_8
195
Open-Circuit Voltage in Organic Solar
Cells
Seiichiro Izawa
8.1 Introduction
Organic solar cells (OSCs) have attracted considerable attention because of their
potential advantages, which include low cost, lightweight, and environmental friendliness [1]. After more than 20 years of research, the power conversion efficiencies
(PCEs) of single-junction OSCs based on blends of electron donor (D) and acceptor
(A) semiconducting materials now exceed 17% [2]. This progress was mainly driven
by the invention of bulk heterojunction device structure at an early stage [3, 4] and
the subsequent development of low-bandgap polymer semiconductors [5]. Recently,
the development of non-fullerene acceptors has brought about a rapid increase in the
PCEs of OSCs [6].
The PCE of OSCs is lower compared to that of other SC devices: GaAs, singlecrystal silicon, and perovskite SCs have PCE values of over 25% [7]. The next
research target for OSCs is to achieve a PCE of a similar level in a highly efficient
SC device. With regard to the current generation properties, the external quantum
efficiencies (EQEs) of OSCs have already exceeded 85% [8], with internal quantum
efficiencies from absorbed photons to electrons close to 100% [9]. Further increases
in the PCE of OSCs is currently limited mainly by the open-circuit voltage (V OC ),
and to achieve additional increases in the PCE, it is therefore very important to clarify
the factors that determine V OC in OSCs, and to find a strategy for improving it.
In this chapter, we first provide the theoretical background explaining how V OC
is determined in OSCs. We then describe recent findings on how the D/A interfacial
properties largely affect V OC , and how it can be improved by controlling the nanostructure at the D/A interface. Finally, we present our conclusions and describe future
prospects for further improvement of V OC in OSCs.
S. Izawa (B)
National Institutes of Natural Science, Institute for Molecular Science, 5-1 Higashiyama
Myodaiji, Aichi, Okazaki 444-8787, Japan
e-mail: izawa@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_8
195