Tailored merocyaninedyes for solution-processed BHJ solar cells

Bürckstümmer, Hannah; Kronenberg, Nils M.; Gsänger, Marcel; Stolte, Matthias; Meerholz, Klaus; Würthner, Frank

doi:10.1039/b916181c

Cited by 127 publications

(131 citation statements)

References 37 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: 80%

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: 80%

Field-dependent exciton dissociation in organic heterojunction solar cells

et al. 2012

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“…It is slightly reduced compared with the pure compound ( μ h = 5 × 10 − 5 cm 2 V − 1 s − 1 ). [ 15 ] Secondly, the absorption spectra were found to be almost identical in the spectral region between 400 and 900 nm, where the dye absorbs (see Fig. 4 ).…”

Section: Direct Comparison Of Highly Effi Cient Solution-and Vacuum-pmentioning

confidence: 96%

“…[ 14 ] Using the sol (spin-coating) approach, power conversion effi ciencies ( PCE ) up to 2.6% have been achieved. [ 15 ] Since the applied MCs are small molecules with rather short alkyl chains they can not only be processed from solution, but some can also be thermally evaporated. In this Communication, we compare the two processing methods for BHJ solar cells using MC dyes as electron donor compounds, selecting those that are suffi ciently soluble and do not thermally decompose upon sublimation.…”

Section: Direct Comparison Of Highly Effi Cient Solution-and Vacuum-pmentioning

confidence: 99%

Direct Comparison of Highly Efficient Solution‐ and Vacuum‐Processed Organic Solar Cells Based on Merocyanine Dyes

et al. 2010

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Identically configured bulk heterojunction organic solar cells based on merocyanine dye donor and fullerene acceptor compounds (see figure) are manufactured either from solution or by vacuum deposition, to enable a direct comparison. Whereas the former approach is more suitable for screening purposes, the latter approach affords higher short-circuit current density and power conversion efficiency.

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“…The semiconductors are arranged in groups of structurally similar compounds. They range from apolar aromatic hydrocarbons (anthracene, [22] rubrene, [23] and DIP [24] ), over triphenylamines [25][26][27] and donor-acceptor-donor compounds (squaraines, [28] and diketopyrrolopyrroles [29] ) to highly polar merocyanines (MD353, [30] and HB194 [31] )…”

Section: Theoretical Approachmentioning

confidence: 99%

“…Thus, besides the more conventional organic semiconductor molecules such as anthracene and rubrene, we also included quadrupolar diketopyrrolopyrrole DPP and squaraine and even two highly dipolar merocyanines because, recently, these dyes and pigments afforded surprisingly good electronic and optoelectronic performances as active semiconducting compounds in organic transistors and solar cells. [32] For the dipolar merocyanines, we chose [31] HB194 and MD353 [33] because, despite their rather different electronic structure, both dyes could be used successfully as donor materials in bulk heterojunction solar cells in combination with C 60 fullerene and its derivative PCBM. Here, HB194 is a more polyene-like dye that shows a strong increase of the dipole moment upon optical excitation whereas MD353 possesses almost equal dipole moments in the ground and excited state, leading to narrow cyanine-type absorption bands.…”

Section: Introductionmentioning

confidence: 99%

QM/MM calculations combined with the dimer approach on the static disorder at organic‐organic interfaces of thin‐film organic solar cells composed of small molecules

Brückner

Stolte²,

Würthner³

et al. 2017

J of Physical Organic Chem

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A QM/MM approach using ωB97X-D combined with AMOEBA calculations was used to analyze the energetic disorder in the vicinity of interfaces in amorphous organic heterostructures. Distributions of ground-, excited-, and cationic-state energies as well as of ionization potentials and excitation energies, all being relevant quantities for the transport properties of thin films, were calculated. As already found for bulk amorphous organic semiconductors, local densities of states at molecular interfaces possess Gaussian-shaped profiles with a significant amount of disorder. Assuming a disorder-limited activation of exciton and charge transport, a decrease in the amount of disorder could improve the transport properties. Relating calculated disorders to molecular parameters revealed that in line with the Bässler model, especially the molecular polarity, its change upon electronic excitation, and the molecular polarizability are relevant quantities leading to energetically largely disordered films. Moreover, because of the different mechanisms of exciton and polaron delocalization, a given morphology with disordered charge-transport levels gives not necessarily rise to disordered exciton-transport levels and vice versa. | INTRODUCTIONDisorder in molecular organic semiconductors has been recognized as a key parameter limiting the semiconductor's transport properties for both charges and excitons. [1] A random distribution of the molecules in a disordered amorphous film results in considerable variations in local intermolecular interactions. This gives rise to a distribution of ionization and excitation energies, the relevant quantities for charge and exciton transport, which depend among others on these intermolecular interaction energies. [2] According to the central limit theorem, resulting densities of states (DOSs) for excitons and charges have a Gaussian shape because intermolecular interaction energies are composed of many independently varying contributions. [3] The width of the Gaussian-shaped DOSs, ie, the standard deviation of the Gaussian normal distribution σ, is referred to as the disorder parameter and characterizes the amount of site energy disorder, ie, of static disorder, in the semiconducting solid-state system. [2] Based on this Gaussian DOS, the Bässler model describes charge transport in organic semiconductors as an incoherent hopping process between the normally distributed sites. [4] The expression "disorder" can be connected with geometrical and energetical disorder. In line with the Bässler nomenclature, in the following the expression, "disorder" is always used to characterize the energetic disorder unless otherwise noted. Although experimentally detected field-and temperature-dependent charge carrier mobilities confirm the predictions of the Bässler model in principle, no direct experimental proof for the Gaussian-shaped DOS, particularly of charge carriers, in disordered molecular semiconductors † This article is published as part of a special issue to celebrate the 80 th birthday of P...

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Tailored merocyaninedyes for solution-processed BHJ solar cells

Cited by 127 publications

References 37 publications

Field-dependent exciton dissociation in organic heterojunction solar cells

Field-dependent exciton dissociation in organic heterojunction solar cells

Direct Comparison of Highly Efficient Solution‐ and Vacuum‐Processed Organic Solar Cells Based on Merocyanine Dyes

QM/MM calculations combined with the dimer approach on the static disorder at organic‐organic interfaces of thin‐film organic solar cells composed of small molecules

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