Charge Generation Kinetics and Transport Mechanisms in Blended Polyfluorene Photovoltaic Devices

Snaith, Henry J.; Arias, Ana Claudia; Morteani, Arne C.; Silva, Carlos; Friend, Richard H.

doi:10.1021/nl0257418

Cited by 211 publications

(217 citation statements)

References 13 publications

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“…The elimination of the nanoscale defect structures from morphologies D to F causes an increase of about 1.23% in the PCE, 24% in the IQE, and 55% in the charge transport efficiency under real-circuit conditions. These observations are in agreement with the experimental findings of Snaith et al, 39 who found through composition analysis and photoluminescence emission spectroscopy experiments on PFB/F8BT-polymer blends that the process of charge transport and not the process of charge generation is the limiting factor of the device performance. We should also point out in this context that several recent experimental and theoretical studies 4,27,37,38,40,42 have demonstrated that structural characteristics can strongly affect the processes of charge generation and recombination as well as charge transport to the electrodes.…”

Section: Resultssupporting

confidence: 93%

“…Recent experiments indicate that such structural characteristics can strongly affect the complementary processes of charge generation and charge recombination as well as the process of charge transport to the electrodes. For example, Coffey and Ginger 37,38 observed very recently with time-resolved electrostatic force microscopy that, contrary to the common belief, 39 the domain centers of their DA-polyfluorene blends provide a much greater contribution to the photocurrent than the region in close proximity to the DA heterojunctions. They explained their observations by the mixing of the D-or A-rich phases with a minority fraction of the other component, which affects charge generation as well as charge transport.…”

Section: Introductionmentioning

confidence: 97%

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A new multiscale modeling method for simulating the loss processes in polymer solar cell nanodevices

Pershin

Donets

Baeurle

2012

The Journal of Chemical Physics

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The photoelectric power conversion efficiency of polymer solar cells is till now, compared to conventional inorganic solar cells, still relatively low with maximum values ranging from 7% to 8%. This essentially relates to the existence of exciton and charge carrier loss phenomena, reducing the performance of polymer solar cells significantly. In this paper we introduce a new computer simulation technique, which permits to explore the causes of the occurrence of such phenomena at the nanoscale and to design new photovoltaic materials with optimized opto-electronic properties. Our approach consists in coupling a mesoscopic field-theoretic method with a suitable dynamic Monte Carlo algorithm, to model the elementary photovoltaic processes. Using this algorithm, we investigate the influence of structural characteristics and different device conditions on the exciton generation and charge transport efficiencies in case of a novel nanostructured polymer blend. More specifically, we find that the disjunction of continuous percolation paths leads to the creation of dead ends, resulting in charge carrier losses through charge recombination. Moreover, we observe that defects are characterized by a low exciton dissociation efficiency due to a high charge accumulation, counteracting the charge generation process. From these observations, we conclude that both the charge carrier loss and the exciton loss phenomena lead to a dramatic decrease in the internal quantum efficiency. Finally, by analyzing the photovoltaic behavior of the nanostructures under different circuit conditions, we demonstrate that charge injection significantly determines the impact of the defects on the solar cell performance.

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Section: Resultssupporting

confidence: 93%

Section: Introductionmentioning

confidence: 97%

A new multiscale modeling method for simulating the loss processes in polymer solar cell nanodevices

Pershin

Donets

Baeurle

2012

The Journal of Chemical Physics

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“…Geminate recombination, bimolecular recombination, and space-charge effects can all play a role, 16 and the exact effect of morphology on each of these processes is still the subject of debate. 17 Further research is required to identify the exact physical origin of the full current-voltage curve, in particular the factors which determine the open-circuit voltage 18 and fill factor. 19 Computational modeling offers a way of investigating these issues and informing ongoing experimental work.…”

Section: Introductionmentioning

confidence: 99%

A microscopic model for the behavior of nanostructured organic photovoltaic devices

Marsh

Groves

Greenham

2007

Journal of Applied Physics

225

233

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Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. We present a Monte Carlo model of carrier separation and recombination in nanostructured organic photovoltaic ͑OPV͒ devices which takes into account all electrostatic interactions, energetic disorder, and polaronic effects. This permits a detailed analysis of the strong morphology dependence of carrier collection efficiency. We find that performance is determined both by the orientation of the heterojunction relative to the external electric field as well as by carrier confinement due to polymer intermixing. The model predicts that an idealized interdigitated structure could achieve overall efficiencies twice as high as blends. The model also reproduces the weakly sublinear intensity dependence of short-circuit photocurrent ͑I SC ͒ seen in experiment. We show that this is not the result of space-charge effects but of bimolecular recombination. Disconnected islands of polymer in coarser blends result in bimolecular recombination even at low intensities and should therefore be minimized. By including a microscopic description of dark injection, the model can describe the full current-voltage ͑J-V͒ characteristics of different OPV structures. We examine the effect of morphology, intensity, mobility, and recombination rate on key parameters such as short-circuit current, open-circuit voltage ͑V OC ͒, and fill factor ͑FF͒. The model reproduces the intensity-dependent contribution to V OC in a bilayer above that of a blend observed in experiment. We find that performance in both bilayers and blends is very sensitive to the recombination rate across the heterojunction. The model also predicts a striking dependence of performance on mobility. Indeed it is shown that a tenfold increase in mobility dramatically improves I SC and FF and doubles the maximum power output in a bilayer device. As well as informing routes for improving device performance, the model also offers an improved microscopic understanding of OPV operation.

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“…6,7 Next to PLEDs, F8BT is also used as active electron donating material in polymer/polymer solar cells, where it is blended with other fluorene based copolymers. [8][9][10][11][12] Furthermore, F8BT has a relatively high electron affinity ͑ϳ3.3 eV͒ and a large ionization potential of ϳ5.9 eV. As a result it can also be used as an electron-acceptor in allpolymer bulk heterojunctions.…”

mentioning

confidence: 99%

Electron and hole transport in poly(fluorene-benzothiadiazole)

Zhang

Blom

2011

Applied Physics Letters

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We investigate the electron and hole transport in poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4,8-diyl)] (F8BT). An Ohmic hole contact on F8BT is achieved by using the high work function anode MoO3 as hole injection contact, enabling the occurrence of space-charge limited currents. The electron transport in F8BT is trap-limited and the traps can be deactivated using n-type doping by decamethylcobaltocene (DMC). Due to the alignment of the energy levels of DMC and F8BT the electrons from the DMC donor not only fill the traps but also fill up the lowest unoccupied molecular orbital of F8BT such that the electron transport can be enhanced beyond the hole transport.

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Charge Generation Kinetics and Transport Mechanisms in Blended Polyfluorene Photovoltaic Devices

Cited by 211 publications

References 13 publications

A new multiscale modeling method for simulating the loss processes in polymer solar cell nanodevices

A new multiscale modeling method for simulating the loss processes in polymer solar cell nanodevices

A microscopic model for the behavior of nanostructured organic photovoltaic devices

Electron and hole transport in poly(fluorene-benzothiadiazole)

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