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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.


Related in: MedlinePlus

FF vs. time of inverted OSCs based on neat and plasmonically sensitized TiOx (a,c) and ZnO (b) during illumination with 1/10 of the AM1.5 radiation with UV spectral range blocked (either λ > 550 nm or λ > 475 nm).Photoactive material is P3HT:PC60BM for (a, b) and PCDTBT:PC70BM for (c–e) (for details see Methods section). (d) and (e) display the J/V characteristics corresponding to the FF data shown in (c).
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f5: FF vs. time of inverted OSCs based on neat and plasmonically sensitized TiOx (a,c) and ZnO (b) during illumination with 1/10 of the AM1.5 radiation with UV spectral range blocked (either λ > 550 nm or λ > 475 nm).Photoactive material is P3HT:PC60BM for (a, b) and PCDTBT:PC70BM for (c–e) (for details see Methods section). (d) and (e) display the J/V characteristics corresponding to the FF data shown in (c).

Mentions: It is now instructive to study these metal-oxides as electron extraction layers in OSCs. Here, the fill factor (FF) is monitored vs. time during illumination with AM1.5 solar light with UV spectral range blocked (Figure 5 a-c). OSCs with non-sensitized metal oxides (TiOx or ZnO) remain in a state of low FF < 40% and thus low PCE (with s-shaped I/V characteristics as seen exemplary in Figure 1b). This situation does not change even if the illumination intensity is increased by an order of magnitude and is extended to 1 h duration. It has to be noted, that the AM1.5 solar spectrum delivers an intensity of about 15 mW/cm2 between 550 and 650 nm. Even if we use a green laser to supply a significantly higher intensity (λ = 532 nm, 700 mW/cm2), the FF of non-sensitized samples remains low after 1 h of continuous illumination. Therefore, the excitation of non-sensitized metal oxides via sub-bandgap defect states does not appear to account for oxygen desorption and the concomitant lowering of the WF. On the contrary, during illumination with a tenfold attenuated AM1.5 solar radiation with UV spectral range blocked, the devices based on plasmonically sensitized electron extraction layers show a continuous improvement of the FF until a saturated state with a high FF and high PCE is reached within less than 5 min (Figure 5 a-c). This finding holds for both TiOx and ZnO layers sensitized by AgNPs and applies regardless of whether P3HT:PC60BM or PCDTBT:PC70BM is used as photoactive layer. Note, a table with the characteristics of the OSC devices studied here can be found in the supporting information (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)

FF vs. time of inverted OSCs based on neat and plasmonically sensitized TiOx (a,c) and ZnO (b) during illumination with 1/10 of the AM1.5 radiation with UV spectral range blocked (either λ > 550 nm or λ > 475 nm).Photoactive material is P3HT:PC60BM for (a, b) and PCDTBT:PC70BM for (c–e) (for details see Methods section). (d) and (e) display the J/V characteristics corresponding to the FF data shown in (c).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f5: FF vs. time of inverted OSCs based on neat and plasmonically sensitized TiOx (a,c) and ZnO (b) during illumination with 1/10 of the AM1.5 radiation with UV spectral range blocked (either λ > 550 nm or λ > 475 nm).Photoactive material is P3HT:PC60BM for (a, b) and PCDTBT:PC70BM for (c–e) (for details see Methods section). (d) and (e) display the J/V characteristics corresponding to the FF data shown in (c).
Mentions: It is now instructive to study these metal-oxides as electron extraction layers in OSCs. Here, the fill factor (FF) is monitored vs. time during illumination with AM1.5 solar light with UV spectral range blocked (Figure 5 a-c). OSCs with non-sensitized metal oxides (TiOx or ZnO) remain in a state of low FF < 40% and thus low PCE (with s-shaped I/V characteristics as seen exemplary in Figure 1b). This situation does not change even if the illumination intensity is increased by an order of magnitude and is extended to 1 h duration. It has to be noted, that the AM1.5 solar spectrum delivers an intensity of about 15 mW/cm2 between 550 and 650 nm. Even if we use a green laser to supply a significantly higher intensity (λ = 532 nm, 700 mW/cm2), the FF of non-sensitized samples remains low after 1 h of continuous illumination. Therefore, the excitation of non-sensitized metal oxides via sub-bandgap defect states does not appear to account for oxygen desorption and the concomitant lowering of the WF. On the contrary, during illumination with a tenfold attenuated AM1.5 solar radiation with UV spectral range blocked, the devices based on plasmonically sensitized electron extraction layers show a continuous improvement of the FF until a saturated state with a high FF and high PCE is reached within less than 5 min (Figure 5 a-c). This finding holds for both TiOx and ZnO layers sensitized by AgNPs and applies regardless of whether P3HT:PC60BM or PCDTBT:PC70BM is used as photoactive layer. Note, a table with the characteristics of the OSC devices studied here can be found in the supporting information (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