Simulating Phase Transition Dynamics on Non-trivial Domains

Bolikowski, Łukasz; Gokieli, Maria

doi:10.1007/978-3-642-55195-6_48

Cited by 2 publications

(4 citation statements)

References 33 publications

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“…Since the interaction energy determines the average domain size of the resulting morphologies, this single parameter allowed us to simulate bulk heterojunction morphologies with a controllably varying average feature size. We employed David Eyre's linearly stabilized Cahn-Hilliard integration scheme [44,45] to solve the Cahn-Hilliard equation on a 2-D grid, an approach that has previously been applied to generate polymer-fullerene BHJ morphologies. [28,29] Although other Cahn-Hilliard-based studies have investigated morphology characteristics such as average feature size [46], annealing time (represented by the C-H integration time), [28] and tortuosity on OPV device performance, [47] for this study, we are primarily interested in the effects of the amorphous, mixed-composition interfacial regions and how such regions may be important for BHJs to function.…”

Section: Cahn-hilliard Generated Morphologiesmentioning

confidence: 99%

Drift-Diffusion Studies of Compositional Morphology in Bulk Heterojunctions: The Role of the Mixed Phase in Photovoltaic Performance

Finck

Schwartz

2016

Phys. Rev. Applied

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The active layers of most OPV devices are constructed from a blend of two organic compounds. The two materials spontaneously segregate into pure component phases during device fabrication, creating a bicontinuous network of conduction pathways that are selective for electron or hole charge carriers. The morphological distribution of these materials within the active layer has long been known to influence charge transport and resulting device performance. In addition to the two purecomponent phases present in these devices, a third, mixed-composition phase exists at the interface between the two pure phases. The exact effects of this mixed-composition phase on OPV device performance are not well understood, although it has been argued that the presence of a mixed phase is necessary for optimal device operation. In this work, we probe the effects of having a mixed-composition, interfacial phase on the performance and charge transport characteristics of organic photovoltaic (OPV) devices through a series of drift-diffusion model simulations. We start with set of model morphologies with only pure component phases and then introduce an interfacial, mixed-phase in a controllable fashion. Our simulations show that a modest amount of mixing initially improves device efficiency by reducing the tortuosity of the device's conduction pathways and easing morphological traps. However, an excessive amount of mixing can actually degrade highconductivity pathways, reducing photovoltaic performance. The point at which mixing switches from being beneficial to instead detrimental to OPV performance differs depending on the average domain size of a device's morphology. Devices with smaller feature sizes are more susceptible to the debilitating effects of overmixing, so that the presence of a mixed-phase may either raise power conversion efficiency by as much as 100% or lower it by as much as 50%, depending on the average domain size and the extent of mixing. This suggests that variations in the amount of mixed-composition phase with different processing conditions is one of the key factors that makes optimizing bulk heterojunction OPV devices difficult.

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Section: Cahn-hilliard Generated Morphologiesmentioning

confidence: 99%

Drift-Diffusion Studies of Compositional Morphology in Bulk Heterojunctions: The Role of the Mixed Phase in Photovoltaic Performance

Finck

Schwartz

2016

Phys. Rev. Applied

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“…Since the mobility profiles generated by our random distribution may or may not be representative of what a carrier encounters in a working device, we also investigated a second way of generating spatially-disordered mobility profiles. Our second method is based on the Cahn-Hillard (C-H) model, which is used to describe the spontaneous phase separation of binary fluids [35]. We note that the C-H formalism has been used in the past to model the spatial structure of the components in bulk heterojunction solar cells [47][48][49].…”

Section: -D Mobility Profiles Built From Cahn-hilliard Morphologiesmentioning

confidence: 99%

“…Our choice to also generate mobility profiles via the C-H formalism allows us to further test the effects of spatial disorder on device performance, by seeing if the way mobility profiles are generated has any significant effect on the results. Thus, we also utilized an ensemble of mobility profiles generated from cross-sections of morphologies determined by solving the Cahn-Hilliard equation [35]:…”

Section: -D Mobility Profiles Built From Cahn-hilliard Morphologiesmentioning

confidence: 99%

“…Our work at this stage intentionally neglects the effects of energetic disorder, which would be expected to accompany structurally disordered morphologies, in order to isolate the effects of structural disorder alone on OPV device physics. We present two methods for generating spatially-disordered mobility profiles: one method where each profile is generated by random sampling from a probability distribution of possible carrier mobilities, and a second method where profiles are generated from the disordered morphologies generated by Cahn-Hilliard (C-H) modeling [34,35]. Both sampling methods result in mobility profiles that contain regions of exceptionally high and/or low mobilities for the carriers.…”

Section: Introductionmentioning

confidence: 99%

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Drift-Diffusion Modeling of the Effects of Structural Disorder and Carrier Mobility on the Performance of Organic Photovoltaic Devices

Finck

Schwartz

2015

Phys. Rev. Applied

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We probe the effects of structural disorder on the performance of organic photovoltaic (OPV) devices via Drift-Diffusion (D-D) modeling. We utilize ensembles of spatially disordered 1-dimensional mobility profiles to approximate the 3-dimensional structural disorder present in actual devices. Each replica in our ensemble approximates one high-conductivity pathway through the threedimensional network(s) present in a polymer-based bulk heterojunction solar cell, so that the ensemble-averaged behavior provides a good approximation to a full 3-dimensional structurally disordered device. Our calculations show that the short circuit current, fill factor and power conversion efficiency of simulated devices are all negatively impacted by the inclusion of structural disorder, but that the open circuit voltage is nearly impervious to structural defects. This is in contrast to energetic disorder, where previous studies found that spatial variation in the energy in OPV active layers causes a decrease in the open circuit voltage. We also show that structural disorder causes the greatest detriment to device performance for feature sizes between 2 nm and 10 nm. Since this is on the same length scale as the fullerene crystallites in experimental devices, it suggests both that controlling structural disorder is critical to the performance of OPV devices and that the effects of structural disorder should be included in future D-D modeling studies of organic solar cells.

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Simulating Phase Transition Dynamics on Non-trivial Domains

Cited by 2 publications

References 33 publications

Drift-Diffusion Studies of Compositional Morphology in Bulk Heterojunctions: The Role of the Mixed Phase in Photovoltaic Performance

Drift-Diffusion Studies of Compositional Morphology in Bulk Heterojunctions: The Role of the Mixed Phase in Photovoltaic Performance

Drift-Diffusion Modeling of the Effects of Structural Disorder and Carrier Mobility on the Performance of Organic Photovoltaic Devices

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