Bulk heterojunction organic solar cells based on merocyanine colorants

Kronenberg, Nils M.; Deppisch, Manuela; Würthner, Frank; Lademann, Hans W. A.; Deing, Kaja; Meerholz, Klaus

doi:10.1039/b813341g

Cited by 177 publications

(147 citation statements)

References 32 publications

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“…This D/A combination yielded an effective band gap E eff = E LUMO,acceptor − E HOMO,donor (where LUMO stands for lowest unoccupied molecular orbital and HOMO stands for highest occupied molecular orbital) of 1.7 eV and thus allowed open-circuit voltages V oc of more than 1 V. Figure 1 shows an overview of the layer sequence, the molecular structures, and the energy levels of the materials used in the cell stack. 28 Bulk heterojunction device results for similar chromophores have been published, 33,34 and it has been shown that these materials can be processed wetchemically from solution as well as by vacuum thermal evaporation. 35 In this work thermal evaporation was used because it allowed for a simpler fabrication of well-defined multilayer structures like PHJ cells.…”

Section: A Methodsmentioning

confidence: 86%

Field-dependent exciton dissociation in organic heterojunction solar cells

et al. 2012

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In organic heterojunction solar cells, the generation of free charge carriers takes place in a multistep process which involves charge transfer (CT) states, that is, bound electron-hole pairs at the interface between donor and acceptor molecules. Past efforts to model the CT-state dissociation during solar cell operation were not able to consistently reproduce the experimentally observed field and temperature dependence. This discrepancy between model and experiment was partly due to the field-dependent free charge carrier collection process, which plays an important role in the widely used bulk heterojunction cell configuration and superimposes a possible field-dependent charge carrier generation process. In order to distinguish between generation and collection of free charge carriers, we propose the planar heterojunction cell configuration as a model system to study the field-dependent charge carrier generation process in organic heterojunction solar cells. We apply this model system to check current CT-state dissociation models against experimental data. Although the models can quantitatively account for the photocurrent's dependence on the applied voltage and the device thickness, they fail to account for the virtually negligible temperature dependence of the field-dependent charge-generation process. This discrepancy is traced back to a common feature of the models: an Arrhenius-like temperature dependence, distinctive of all processes involving a thermally activated jump over an energy barrier. As a solution to the problem, we introduce an exciton dissociation model based on a field-dependent tunnel process and demonstrate its consistency with the experimental observations. Our results indicate that the current microscopic picture of the charge-generation process in organic heterojunction solar cells being limited by the CT-state dissociation process needs to be reconsidered.

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Section: A Methodsmentioning

confidence: 86%

Field-dependent exciton dissociation in organic heterojunction solar cells

et al. 2012

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“…7 Recently, the first BHJ solar cells that are based entirely on small conjugated molecules (i.e., PCBM as electron acceptor and various electron donor components) have been published, indicating the increasing interest in this emerging research field. [8][9][10][11][12][13][14][15][16][17][18][19][20] With dendrimers or oligomers based on typical organic semiconductors derived from oligothiophenes, PCE values up to 2.5% could be achieved.…”

Section: Introductionmentioning

confidence: 94%

Optimized solution-processed merocyanine:PCBM organic bulk heterojunction solar cell

Kronenberg

2011

J. Photon. Energy

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Abstract. We present the in-depth investigation of solution-processed bulk-heterojunction solar cells based on the merocyanine dye MD304 as a donor in combination with the soluble fullerene derivative [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) as acceptor. The optimized MD304:PCBM devices exhibit an external quantum efficiency of ca. 50%, and a power conversion efficiency of up to 2.1% under standard illumination and 2.7% under reduced illumination intensities. Because of the strongly dipolar character of merocyanine dyes the bulk material features a relatively large dielectric constant, which is beneficial for charge transport and reduced carrier recombination. This somewhat compensates the limited hole mobility of the dipolar merocyanine. C 2011 Society of Photo-Optical Instrumentation Engineers.

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“…Second, because of increase in charge carrier transfer throughout the PCBM rich domains in the solar cell active layer. The transport of photogenerated charges through the active layer seems to improve with the increasing PCBM content [32]. The PCBM rich domains in the blends may assist charge collection in the high PCBM content blends, owing to the high electron mobility in the PCBM [34].…”

Section: Device Performance Under White Lightmentioning

confidence: 99%

“…The largest value of V OC in Figure 6 is 0.31 V, which may be small in comparison with the difference between the HOMO of the donor and the LUMO of the acceptor, with assumption that the results of cyclic voltammetry from [15,16] are accurate for the materials. This can be explained by the fact that the electrochemical studies are carried out for dissolved molecules in solution, while tightly packed π-π aggregates are formed in the solid state; thus, it is assumed that the redox potentials of individual molecules in solution do not properly reflect the energetic situation in a solid material, and hence in the actual device [32]. This leads to an alteration of the frontier orbital energies of molecules in C6:PCBM composite compared to those of isolated molecular species.…”

Section: External Photocurrent Quantum Efficiency Spectramentioning

confidence: 99%

Investigation of PCBM Concentration on the Performance of Small Organic Solar Cell

Ismail

Soga

Jimbo

2012

ISRN Renewable Energy

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We have fabricated bulk heterojunction organic solar cells using coumarin 6 (C6) as a small organic dye, for light harvesting and electron donating, with fullerene derivative [6,6]-phenyl-C 61 butyric acid methyl ester (PCBM), acting as an electron acceptor, by spin-coating technique of the blend solutions. We have studied effect of PCBM concentration on photocurrent and performance parameters of the solar cells. We found that the optical absorption of the dye increased with increasing its concentration in the active layer blends. The higher concentrations of PCBM in active layer enhanced the photocurrent of the solar cells, as a result of improving charge carrier separation and electron transport in solar cell active layer. The improved charge carrier separation between C6, as a donor, and PCBM, as an acceptor, was indicated through the formation of bulk heterojunction by blending C6 with PCBM. The formation of C6:PCBM bulk heterojunction blend was confirmed through the symbatic behavior of the corresponding solar cell and, also, through the homogeneity and smoothing in the atomic force microscopy images of the C6:PCBM blend films. For the same reasons, the performance parameters of the C6:PCBM solar cell improved by modification of the PCBM concentration in the solar cell active layer.

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Bulk heterojunction organic solar cells based on merocyanine colorants

Cited by 177 publications

References 32 publications

Field-dependent exciton dissociation in organic heterojunction solar cells

Field-dependent exciton dissociation in organic heterojunction solar cells

Optimized solution-processed merocyanine:PCBM organic bulk heterojunction solar cell

Investigation of PCBM Concentration on the Performance of Small Organic Solar Cell

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