Origin of the Efficient Polaron-Pair Dissociation in Polymer-Fullerene Blends

Deibel, Carsten; Strobel, Thomas; Dyakonov, Vladimir

doi:10.1103/physrevlett.103.036402

Cited by 335 publications

(361 citation statements)

References 25 publications

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“…Because the exciton dissociation is an energy-releasing process, an energy barrier hindering the dissociation can be tunneled. In contrast to the Miller-Abrahams hopping, 42 which is a combination of a field-independent tunneling term and a field-dependent Boltzmann factor and has been utilized to model the CT-state dissociation at the D/A interface, 19,43,44 we propose a field-dependent tunnel process which takes into account the polarizability of the excited donor molecules. Figure 5 shows a schematic of the field-dependent tunnel process.…”

Section: A Field-dependent Ct-state Dissociation Modelmentioning

confidence: 99%

“…The obtained lower limit for the inverse localization radius γ 7.7 × 10 9 m −1 was plausible and agreed with values used for modeling in the literature. 19 Note that the above-mentioned estimates for r tunnel,0 , α, and γ were used to check the plausibility of the obtained fit parameter values. They were not used in the fitting process.…”

Section: A Influence Of the Cell Thicknessmentioning

confidence: 99%

“…One issue was the large discrepancy between modeled and experimental CT-state lifetimes τ CT . While experiments determined τ CT to be a few nanoseconds, 12,13,17 the OB model required τ CT to be on the order of microseconds [8][9][10][11]18,19 to milliseconds 20 in order to reproduce the observed internal quantum efficiencies of up to 100%. 21 Moreover, the influence of the device thickness could not be reproduced, 11,22 and two publications on BHJ cells made of poly(3-hexyl-thiophene) (P3HT) and the fullerene derivative [6,6]-phenyl-C61 butyric-acid methylester (PCBM) reported contradictory results for the material system's zero field CT-state dissociation probability p CT,0 of 40%-60% and 90%, respectively.…”

Section: Introductionmentioning

confidence: 99%

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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 Field-dependent Ct-state Dissociation Modelmentioning

confidence: 99%

Section: A Influence Of the Cell Thicknessmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Field-dependent exciton dissociation in organic heterojunction solar cells

et al. 2012

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“…1,2 However, the dominant charge carrier loss mechanism determining the photocurrent is still under discussion. The relevant processes during which the losses can occur are geminate recombination during polaron pair dissociation 3,4 , nongeminate recombination during transport of the already separated polarons 5,6 , and charge extraction from the device. 7,8 A detailed analysis considering the interplay of these mechanisms has still to be done, as already the separate processes are not completely described yet.…”

Section: Introductionmentioning

confidence: 99%

Origin of reduced polaron recombination in organic semiconductor devices

2009

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We propose a model to explain the reduced bimolecular recombination rate found in state-of-the-art bulk heterojunction solar cells. When compared to the Langevin recombination, the experimentally observed rate is one to four orders of magnitude lower, but gets closer to the Langevin case for low temperatures. Our model considers the organic solar cell as device with carrier concentration gradients, which form due to the electrode/blend/electrode device configuration. The resulting electron concentration under working conditions of a solar cell is higher at the cathode than at the anode, and vice versa for holes. Therefore, the spatially dependent bimolecular recombination rate, proportional to the local product of electron and hole concentration, is much lower as compared to the calculation of the recombination rate based on the extracted and thus averaged charge carrier concentrations. We consider also the temperature dependence of the recombination rate, which can for the first time be described with our model.

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“…Field-assisted generation in PPV-based blends was recently confirmed 824 by Mingebach et al [167]. The Braun-Onsager model was also applied to describe 825 the J/V characteristics of P3HT:PCBM solar cells [73,168], but this analysis 826 yielded long CT lifetimes of at least 100 ns [159].…”

mentioning

confidence: 99%

P3HT-Based Solar Cells: Structural Properties and Photovoltaic Performance

Moulé

Neher

Turner

2014

P3HT Revisited – From Molecular Scale to Solar Cell Devices

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Each year we are bombarded with B.Sc. and Ph.D. applications from 8 students that want to improve the world. They have learned that their future depends 9 on changing the type of fuel we use and that solar energy is our future. The hope and 10 energy of these young people will transform future energy technologies, but it will 11 not happen quickly. Organic photovoltaic devices are easy to draw AU1, but the mate-12 rials, processing steps, and ways of measuring the properties of the materials are 13 very complicated. It is not trivial to make a systematic measurement that will 14 change the way other research groups think or practice. In approaching this chapter, 15 we thought about what a new researcher would need to know about organic 16 photovoltaic devices and materials in order to have a good start in the subject. [1][2][3][4]. Similar 43 to the gold rush in the 1800s and the oil boom in the 1900s, intellectual property on 44 new technologies is now the boom industry for innovative people to become rich 45 and influential fast. In the twenty-first century, scientists and engineers are the 46 pioneers and our ideas are the prize. One of the most alluring energy technologies of 47 the past decade has been organic photovoltaics (OPV). This technology is alluring 48 because it could potentially reduce the cost of producing photovoltaic 49 (PV) modules and thereby make solar energy cost-competitive with fossil fuels. 50 As can be seen in Fig. 1, the allure of OPV brought thousands of scientists and 51 engineers into this new field, generating an exponential increase in scientific 52 knowledge (as measured by the number of scientific AU4 articles) in this area. The 53 sharp focus on OPV technology has led to an explosion of interest in enabling 54 technologies such as polymer synthesis, polymer physics, microstructural measure-55 ment techniques, multiscale modeling, photophysics, organic electronics, organic-56 inorganic hybrid materials, etc. All of this intense focus into one research area has 57 also created intense competition between research groups. With so many new 58 scientific articles published yearly, it is impossible to read them all, and repeat or 59 redundant articles have become unfortunately and unavoidably common. Even 60 review articles and books about OPV have proliferated, making production of an 61 original perspective difficult and a complete literature review impractical. We 62 apologize in advance if any important work is not cited here. 63Under this backdrop, we have decided to produce an article that is designed to be 64 helpful to students and postdocs who are entering this field. Rather than focusing on 65 the efficiency of devices or the morphology of materials (subjects that are covered 66 very well elsewhere), we instead focus some attention on how to approach OPV 67 research from a more practical (laboratory-based) perspective. Section 1 introduces A.J. Moulé et al. 68OPV devices, modules, and scale-up. Section 2 discusses fabrication of poly-3- Device Characterist...

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Origin of the Efficient Polaron-Pair Dissociation in Polymer-Fullerene Blends

Cited by 335 publications

References 25 publications

Field-dependent exciton dissociation in organic heterojunction solar cells

Field-dependent exciton dissociation in organic heterojunction solar cells

Origin of reduced polaron recombination in organic semiconductor devices

P3HT-Based Solar Cells: Structural Properties and Photovoltaic Performance

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