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Plasmonically sensitized metal-oxide electron extraction layers for organic solar cells.

Trost S, Becker T, Zilberberg K, Behrendt A, Polywka A, Heiderhoff R, Görrn P, Riedl T - Sci Rep (2015)

Bottom Line: It is shown that in the plasmonically sensitized metal-oxides the illumination with visible light lowers the WF due to desorption of previously ionosorbed oxygen, in analogy to the process found in neat metal oxides upon UV exposure, only.As underlying mechanism the transfer of hot holes from the metal to the oxide upon illumination with hν < Eg is verified.The general applicability of this concept to most common metal-oxides (e.g. TiOx and ZnO) in combination with different photoactive organic materials is demonstrated.

View Article: PubMed Central - PubMed

Affiliation: Institute of Electronic Devices, University of Wuppertal, Rainer-Gruenter-Str. 21, 42119 Wuppertal, Germany.

ABSTRACT
ZnO and TiOx are commonly used as electron extraction layers (EELs) in organic solar cells (OSCs). A general phenomenon of OSCs incorporating these metal-oxides is the requirement to illuminate the devices with UV light in order to improve device characteristics. This may cause severe problems if UV to VIS down-conversion is applied or if the UV spectral range (λ < 400 nm) is blocked to achieve an improved device lifetime. In this work, silver nanoparticles (AgNP) are used to plasmonically sensitize metal-oxide based EELs in the vicinity (1-20 nm) of the metal-oxide/organic interface. We evidence that plasmonically sensitized metal-oxide layers facilitate electron extraction and afford well-behaved highly efficient OSCs, even without the typical requirement of UV exposure. It is shown that in the plasmonically sensitized metal-oxides the illumination with visible light lowers the WF due to desorption of previously ionosorbed oxygen, in analogy to the process found in neat metal oxides upon UV exposure, only. As underlying mechanism the transfer of hot holes from the metal to the oxide upon illumination with hν < Eg is verified. The general applicability of this concept to most common metal-oxides (e.g. TiOx and ZnO) in combination with different photoactive organic materials is demonstrated.

No MeSH data available.


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Optical spectra of (1-T⊥-R⊥) for TiOx, TiOx coated with 0.6 nm of Ag and TiOx/AgNP/TiOx (3 nm) in linear (a) and logarithmic (b) representation, to allow for a magnified view of the absorption in the sub-bandgap region.Corresponding spectra of the analogous samples based on ZnO (c, d). The overall layer thickness is 100 nm. T⊥ and R⊥ denote the transmission and reflection measured normal to the sample surface (see Methods).
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f3: Optical spectra of (1-T⊥-R⊥) for TiOx, TiOx coated with 0.6 nm of Ag and TiOx/AgNP/TiOx (3 nm) in linear (a) and logarithmic (b) representation, to allow for a magnified view of the absorption in the sub-bandgap region.Corresponding spectra of the analogous samples based on ZnO (c, d). The overall layer thickness is 100 nm. T⊥ and R⊥ denote the transmission and reflection measured normal to the sample surface (see Methods).

Mentions: Regarding their optical properties, the AgNP sensitized TiOx layers show a pronounced spectral signature in the sub-bandgap region of the metal-oxide (Figure 3). Instead of the sometimes ambiguous use of “absorption”, we decided to use (1-T⊥-R⊥), instead. Here, T⊥ and R⊥ are the transmission and reflection measured perpendicular to the sample surface (“specular”). In perfectly planar thin film stacks light neither reflected nor transmitted can be attributed to absorption within the stack. On the other hand, with silver nanoparticles involved light missing in specular direction may also be scattered diffusively (Figure S2b). Hence, in the spectral region of the plasmon resonance a significant part of (1-T⊥-R⊥) can be attributed to scattering45. Thus, for a solar cell, the spectral signature found in the plasmonically sensitized samples does not a–priori imply attenuation of the incident solar intensity and in fact no drop in Jsc is found in the corresponding OSCs (see e.g. Figure 1b and Table S1). The spectral difference of the external quantum efficiency (EQE) of an OSC based on neat TiOx and a plasmonically sensitized TiOx layer, respectively, is shown in the supporting information (Figure S3). The EQE of the OSCs with plasmonically sensitized TiOx layer is somewhat higher for λ > 500 nm. This may be attributed to plasmonic scattering of the incident light, accounting for improved in-coupling. This is in agreement with the scattering spectra showing an onset at 500 nm (Figure S2b). As a result of the EQE data, a difference of Jsc for the two cells of about 0.5 mA/cm2 is derived. This is in agreement with the characteristics given in Table S1.


Plasmonically sensitized metal-oxide electron extraction layers for organic solar cells.

Trost S, Becker T, Zilberberg K, Behrendt A, Polywka A, Heiderhoff R, Görrn P, Riedl T - Sci Rep (2015)

Optical spectra of (1-T⊥-R⊥) for TiOx, TiOx coated with 0.6 nm of Ag and TiOx/AgNP/TiOx (3 nm) in linear (a) and logarithmic (b) representation, to allow for a magnified view of the absorption in the sub-bandgap region.Corresponding spectra of the analogous samples based on ZnO (c, d). The overall layer thickness is 100 nm. T⊥ and R⊥ denote the transmission and reflection measured normal to the sample surface (see Methods).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4296292&req=5

f3: Optical spectra of (1-T⊥-R⊥) for TiOx, TiOx coated with 0.6 nm of Ag and TiOx/AgNP/TiOx (3 nm) in linear (a) and logarithmic (b) representation, to allow for a magnified view of the absorption in the sub-bandgap region.Corresponding spectra of the analogous samples based on ZnO (c, d). The overall layer thickness is 100 nm. T⊥ and R⊥ denote the transmission and reflection measured normal to the sample surface (see Methods).
Mentions: Regarding their optical properties, the AgNP sensitized TiOx layers show a pronounced spectral signature in the sub-bandgap region of the metal-oxide (Figure 3). Instead of the sometimes ambiguous use of “absorption”, we decided to use (1-T⊥-R⊥), instead. Here, T⊥ and R⊥ are the transmission and reflection measured perpendicular to the sample surface (“specular”). In perfectly planar thin film stacks light neither reflected nor transmitted can be attributed to absorption within the stack. On the other hand, with silver nanoparticles involved light missing in specular direction may also be scattered diffusively (Figure S2b). Hence, in the spectral region of the plasmon resonance a significant part of (1-T⊥-R⊥) can be attributed to scattering45. Thus, for a solar cell, the spectral signature found in the plasmonically sensitized samples does not a–priori imply attenuation of the incident solar intensity and in fact no drop in Jsc is found in the corresponding OSCs (see e.g. Figure 1b and Table S1). The spectral difference of the external quantum efficiency (EQE) of an OSC based on neat TiOx and a plasmonically sensitized TiOx layer, respectively, is shown in the supporting information (Figure S3). The EQE of the OSCs with plasmonically sensitized TiOx layer is somewhat higher for λ > 500 nm. This may be attributed to plasmonic scattering of the incident light, accounting for improved in-coupling. This is in agreement with the scattering spectra showing an onset at 500 nm (Figure S2b). As a result of the EQE data, a difference of Jsc for the two cells of about 0.5 mA/cm2 is derived. This is in agreement with the characteristics given in Table S1.

Bottom Line: It is shown that in the plasmonically sensitized metal-oxides the illumination with visible light lowers the WF due to desorption of previously ionosorbed oxygen, in analogy to the process found in neat metal oxides upon UV exposure, only.As underlying mechanism the transfer of hot holes from the metal to the oxide upon illumination with hν < Eg is verified.The general applicability of this concept to most common metal-oxides (e.g. TiOx and ZnO) in combination with different photoactive organic materials is demonstrated.

View Article: PubMed Central - PubMed

Affiliation: Institute of Electronic Devices, University of Wuppertal, Rainer-Gruenter-Str. 21, 42119 Wuppertal, Germany.

ABSTRACT
ZnO and TiOx are commonly used as electron extraction layers (EELs) in organic solar cells (OSCs). A general phenomenon of OSCs incorporating these metal-oxides is the requirement to illuminate the devices with UV light in order to improve device characteristics. This may cause severe problems if UV to VIS down-conversion is applied or if the UV spectral range (λ < 400 nm) is blocked to achieve an improved device lifetime. In this work, silver nanoparticles (AgNP) are used to plasmonically sensitize metal-oxide based EELs in the vicinity (1-20 nm) of the metal-oxide/organic interface. We evidence that plasmonically sensitized metal-oxide layers facilitate electron extraction and afford well-behaved highly efficient OSCs, even without the typical requirement of UV exposure. It is shown that in the plasmonically sensitized metal-oxides the illumination with visible light lowers the WF due to desorption of previously ionosorbed oxygen, in analogy to the process found in neat metal oxides upon UV exposure, only. As underlying mechanism the transfer of hot holes from the metal to the oxide upon illumination with hν < Eg is verified. The general applicability of this concept to most common metal-oxides (e.g. TiOx and ZnO) in combination with different photoactive organic materials is demonstrated.

No MeSH data available.


Related in: MedlinePlus