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Analytical model for the photocurrent-voltage characteristics of bilayer MEH-PPV/TiO2 photovoltaic devices.

Chen C, Wu F, Geng H, Shen W, Wang M - Nanoscale Res Lett (2011)

Bottom Line: An analytical model is developed for the photocurrent-voltage characteristics of the bilayer polymer/TiO2 photovoltaic cells.Bilayer polymer/TiO2 cells consisting of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and TiO2, with different thicknesses of the polymer and TiO2 films, were prepared for experimental purposes.The experimental results for the prepared bilayer MEH-PPV/TiO2 cells under different conditions are satisfactorily fitted to the model.

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Affiliation: Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, PR China. mtwang@ipp.ac.cn.

ABSTRACT
The photocurrent in bilayer polymer photovoltaic cells is dominated by the exciton dissociation efficiency at donor/acceptor interface. An analytical model is developed for the photocurrent-voltage characteristics of the bilayer polymer/TiO2 photovoltaic cells. The model gives an analytical expression for the exciton dissociation efficiency at the interface, and explains the dependence of the photocurrent of the devices on the internal electric field, the polymer and TiO2 layer thicknesses. Bilayer polymer/TiO2 cells consisting of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and TiO2, with different thicknesses of the polymer and TiO2 films, were prepared for experimental purposes. The experimental results for the prepared bilayer MEH-PPV/TiO2 cells under different conditions are satisfactorily fitted to the model. Results show that increasing TiO2 or the polymer layer in thickness will reduce the exciton dissociation efficiency in the device and further the photocurrent. It is found that the photocurrent is determined by the competition between the exciton dissociation and charge recombination at the donor/acceptor interface, and the increase in photocurrent under a higher incident light intensity is due to the increased exciton density rather than the increase in the exciton dissociation efficiency.

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Schematic band diagram for a bilayer TiO2/MEH-PPV device under (a) E > 0 and (b) E < 0.
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Figure 3: Schematic band diagram for a bilayer TiO2/MEH-PPV device under (a) E > 0 and (b) E < 0.

Mentions: In a bilayer device, the electrons are injected into the acceptor layer and the holes remain in the donor layer after the interfacial exciton dissociation [39]. In other words, each charge carrier is in its respective phase. Therefore, in our case, the charge recombination in single polymer or TiO2 layer can be ignored. However, the recombination at the D/A interface must be considered. The presence of the internal electric field in the device may affect the charge-transport properties and also the charge recombination and exciton dissociation rates at the D/A interface. In our model, the exciton dissociation efficiency ηCT is expressed in terms of the ratio between exciton recombination and separation. As shown in Figure 3a, when applying a forward internal electric field (E > 0), the drift and diffusion currents of the electrons (holes) in the TiO2 (polymer) layer are in the same direction, the electric field contributes to suppress the recombination of injected electrons in TiO2 with holes in the highest-occupied molecular orbital (HOMO) of the polymer by accelerating their separation at the polymer/TiO2 interface.


Analytical model for the photocurrent-voltage characteristics of bilayer MEH-PPV/TiO2 photovoltaic devices.

Chen C, Wu F, Geng H, Shen W, Wang M - Nanoscale Res Lett (2011)

Schematic band diagram for a bilayer TiO2/MEH-PPV device under (a) E > 0 and (b) E < 0.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211440&req=5

Figure 3: Schematic band diagram for a bilayer TiO2/MEH-PPV device under (a) E > 0 and (b) E < 0.
Mentions: In a bilayer device, the electrons are injected into the acceptor layer and the holes remain in the donor layer after the interfacial exciton dissociation [39]. In other words, each charge carrier is in its respective phase. Therefore, in our case, the charge recombination in single polymer or TiO2 layer can be ignored. However, the recombination at the D/A interface must be considered. The presence of the internal electric field in the device may affect the charge-transport properties and also the charge recombination and exciton dissociation rates at the D/A interface. In our model, the exciton dissociation efficiency ηCT is expressed in terms of the ratio between exciton recombination and separation. As shown in Figure 3a, when applying a forward internal electric field (E > 0), the drift and diffusion currents of the electrons (holes) in the TiO2 (polymer) layer are in the same direction, the electric field contributes to suppress the recombination of injected electrons in TiO2 with holes in the highest-occupied molecular orbital (HOMO) of the polymer by accelerating their separation at the polymer/TiO2 interface.

Bottom Line: An analytical model is developed for the photocurrent-voltage characteristics of the bilayer polymer/TiO2 photovoltaic cells.Bilayer polymer/TiO2 cells consisting of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and TiO2, with different thicknesses of the polymer and TiO2 films, were prepared for experimental purposes.The experimental results for the prepared bilayer MEH-PPV/TiO2 cells under different conditions are satisfactorily fitted to the model.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, PR China. mtwang@ipp.ac.cn.

ABSTRACT
The photocurrent in bilayer polymer photovoltaic cells is dominated by the exciton dissociation efficiency at donor/acceptor interface. An analytical model is developed for the photocurrent-voltage characteristics of the bilayer polymer/TiO2 photovoltaic cells. The model gives an analytical expression for the exciton dissociation efficiency at the interface, and explains the dependence of the photocurrent of the devices on the internal electric field, the polymer and TiO2 layer thicknesses. Bilayer polymer/TiO2 cells consisting of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and TiO2, with different thicknesses of the polymer and TiO2 films, were prepared for experimental purposes. The experimental results for the prepared bilayer MEH-PPV/TiO2 cells under different conditions are satisfactorily fitted to the model. Results show that increasing TiO2 or the polymer layer in thickness will reduce the exciton dissociation efficiency in the device and further the photocurrent. It is found that the photocurrent is determined by the competition between the exciton dissociation and charge recombination at the donor/acceptor interface, and the increase in photocurrent under a higher incident light intensity is due to the increased exciton density rather than the increase in the exciton dissociation efficiency.

No MeSH data available.


Related in: MedlinePlus