Simulation of loss mechanisms in organic solar cells: A description of the mesoscopic Monte Carlo technique and an evaluation of the first reaction method

Groves, Chris; Kimber, Robin G. E.; Walker, Alison B.

doi:10.1063/1.3483603

Cited by 51 publications

(49 citation statements)

References 44 publications

(73 reference statements)

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“…The various permitted behaviors of each particle can be determined by a series of rate coefficients, k, for the physical, kinetic processes that occur within the device. These are not just limited to carrier hopping -for example, many KMC studies have also considered photo and electrical injection, exciton transport and dissociation, and carrier recombination in order to simulate a complete electronic device [95,97,98,100]. Generally, the simulations proceed as follows.…”

Section: Charge Mobilitymentioning

confidence: 99%

“…While both contributions are material dependent, density functional theory and alternative theoretical treatments predict that λ ext is independent of chromophore length, whereas λ int decreases monotonically for longer chromophores [117][118][119]. Some investigations have had success from approximating the reorganization energy to be twice the charge carrier polaron energy, which can be tuned to match the simulated material [100,120,121], rather than explicitly calculating λ ij through QCCs or molecular dynamics [122,123].…”

Section: Charge Mobilitymentioning

confidence: 99%

“…The exponential term contains the free-energy difference between the initial and final hopping states, ∆E ij = E j − E i , and therefore represents a penalty associated with hops across energies with magnitudes significantly greater than λ ij . The majority of other investigations that employ this semi-classical Marcus treatment use a lattice-based model of a complete active layer, the morphology of which can be inferred from MD simulations [93], or by numerical methods such as modified Cahn-Hilliard [94][95][96][97] or Ising model techniques [98][99][100]. In these cases, the free energy, ∆E ij , takes into account any local variation in the energy levels (which is often selected from a density of state (DoS) distribution), the Coulomb interactions between nearby charge carriers and their images, as well as any contributions from the applied electric field across the morphology [96,97,101,102].…”

Section: Charge Mobilitymentioning

confidence: 99%

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Computationally connecting organic photovoltaic performance to atomistic arrangements and bulk morphology

Jones

Jankowski

2017

Molecular Simulation

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Rationally designing roll-to-roll printed organic photovoltaics requires a fundamental understanding of active layer morphologies optimized for charge separation and transport, and which ingredients can be used to self-assemble those morphologies. In this review article we discuss advances in three areas of computational modeling that provide insight into active layer morphology and the charge transport properties that result. We explain the computational bottlenecks prohibiting atomistically-detailed simulations of device-scale active layers and the coarse-graining and hardware acceleration strategies for overcoming them. We review coarse-grained simulations of organic photovoltaic active layers and show that high throughput simulations of experimentally-relevant length scales are now accessible. We describe a new Python package diffractometer that permits grazing-incidence X-ray scattering patterns of simulated active layers to be compared against experiments. We explain the accurate calculation of charge-carrier mobilities from coarse-grained active layer morphologies by using atomistic backmapping, quantum chemical calculations, and kinetic Monte Carlo simulations. We employ these simulations to show that ordering of poly(3-hexylthiophene-2,5-diyl) explains a factor of 1000 improvement in charge mobility. In concert, we present a suite of computational tools enabling large-scale electronic properties of organic photovoltaics to be studied and screened for by molecular simulations.

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Section: Charge Mobilitymentioning

confidence: 99%

Section: Charge Mobilitymentioning

confidence: 99%

Section: Charge Mobilitymentioning

confidence: 99%

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Computationally connecting organic photovoltaic performance to atomistic arrangements and bulk morphology

Jones

Jankowski

2017

Molecular Simulation

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“…MC simulations have been applied earlier to study exciton diffusion and relaxation processes in organic materials [22][23][24] and excitonic processes determining the efficiency of photovoltaic devices. [25][26][27] We employ MC simulations to study how in a transient PL experiment the timedependent emission varies as a function of both the dye and triplet exciton concentrations, for a range of realistic microscopic-scale parameters which describe the exciton diffusion and long-range dipole-dipole interaction processes. We consider a mixed mechanism in which both processes are included.…”

Section: Introductionmentioning

confidence: 99%

Kinetic Monte Carlo study of triplet-triplet annihilation in organic phosphorescent emitters

Eersel

Bobbert

Coehoorn

2015

Journal of Applied Physics

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The triplet-triplet annihilation (TTA) rate in organic phosphorescent materials such as used in organic light-emitting diodes is determined predominantly either by the rate of single-step Förster-type triplet-triplet interactions, or by multi-step triplet diffusion. We show how kinetic Monte Carlo simulations may be used to analyze the role of both processes. Under steady state conditions, the effective triplet-triplet interaction rate coefficient, kTT, which is often regarded as a constant, is found to depend actually on the number of excitons lost upon a triplet-triplet interaction process and to show a significant higher-order dependence on the triplet volume density. Under the conditions encountered in transient photoluminescence (PL) studies, kTT is found to be effectively constant in the case of diffusion-dominated TTA. However, for the case of single-step TTA, a strongly different decay of the emission intensity is found, which also deviates from an analytic expression proposed in the literature. We discuss how the transient PL response may be used to make a distinction between both mechanisms. The simulations are applied to recently published work on the dye concentration dependence of the TTA rate in materials based on the archetypal green emitter tris[2-phenylpyridine]iridium (Ir(ppy)3).

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“…By introducing the energetic disorder to the density of states distribution, the fill factor can be simulated in the numerical drift-diffusion model, and the results could provide a design guidance for new polymer synthesis. could also be used to analyze the effect of morphology on the performance of organic photovoltaics [162,163].…”

Section: Relationship Between Energetic Disorder and Fill Factor By Nmentioning

confidence: 99%

Photocurrent Limiting Mechanisms in Organic Bulk Heterojunction Solar Cells

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As we use more energy as a society, there is a greater need to become less reliant on non-renewable energy sources. Photovoltaics (PV), as a method of harvesting sunlight and converting it into electricity, provide a potential way of producing clean renewable energy.Organic bulk heteojunction (BHJ) solar cells featured with low-cost, large-area and thin-film manufacture, have become more viable with the recent demonstration with power conversion efficiencies (PCE) as high as10.7%. However, there is still a room for further improvement to reach the thermodynamic PCE limit of ~22%. For organic BHJ solar cells, the efficiency is essentially limited by the low short-circuit current density, which is determined by four sequential steps that are necessary to transform incident photons to free charge carriers. These steps are photo absorption and exciton formation, exciton diffusion, polaron pair dissociation and free polaron collection. In order to know the extent to which each of these steps limits the efficiency, a systematic study to analyze the limiting mechanisms is beneficial.In this work, we report approaches that are capable of providing insight into these processes by applying several complementary experimental techniques and theoretical calculations. The material system that are studied are poly(3-hexylthiophene) (P3HT): Therefore, it is quite intrigue to explore the reasons behind that.For absorption, the optical transfer-matrix theory is applied on the multi-thinlayer structure of organic BHJ solar cells. The complex refractive index is extracted.Meanwhile, the optical electric field and the absorption efficiency are calculated and iii AcknowledgementThe Ph.D study is a strict but a joyful scientific training. To make through it, I'd like to thank to the people who gave me tremendous support in these years.First and foremost I would like to thank my supervisor, Dr. Joe C. Campbell, for his patient guidance, continual support and encouragement during my Ph.D study. I learned a lot from him, not only about how to tackle the experimental/theoretical problems, but also about the vision, the presentation skills, and the way to keep a good relationship with your collaborators. I also appreciate the research freedom that Dr. Joe C. Campbell gave to me, which allows me to deliberate, to try and to pursuit without worrying.

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Simulation of loss mechanisms in organic solar cells: A description of the mesoscopic Monte Carlo technique and an evaluation of the first reaction method

Cited by 51 publications

References 44 publications

Computationally connecting organic photovoltaic performance to atomistic arrangements and bulk morphology

Computationally connecting organic photovoltaic performance to atomistic arrangements and bulk morphology

Kinetic Monte Carlo study of triplet-triplet annihilation in organic phosphorescent emitters

Photocurrent Limiting Mechanisms in Organic Bulk Heterojunction Solar Cells

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