Langevin recombination and space-charge-perturbed current transients in regiorandom poly(3-hexylthiophene)

Pivrikas, Almantas; Juška, G.; Österbacka, Ronald; Westerling, M.; Viliũnas, M.; Arlauskas, K.; Stubb, H.

doi:10.1103/physrevb.71.125205

Cited by 74 publications

(60 citation statements)

References 20 publications

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“…[34][35][36] The recombination coefficient can be estimated from the amount of charge extracted during a TOF experiment. 4,37,38 However, the external circuit resistance influences the extracted charge, 9 making the measurement unreliable due to its dependence on the experimental conditions. Previous works have neglected the impact of the RC circuit.…”

Section: Introductionmentioning

confidence: 99%

Molecular weight dependent bimolecular recombination in organic solar cells

Philippa

Stolterfoht

White

et al. 2014

The Journal of Chemical Physics

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Charge carrier recombination is studied in operational organic solar cells made from the polymer:fullerene system PCDTBT:PC71BM (poly[N-9"-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2thienyl-2',1',3'-benzothiadiazole)] : [6,6]-phenyl-C 70 -butyric acid methyl ester). A newly developed technique High Intensity Resistance dependent PhotoVoltage (HI-RPV) is presented for reliably quantifying the bimolecular recombination coefficient independently of variations in experimental conditions, thereby resolving key limitations of previous experimental approaches. Experiments are performed on solar cells of varying thicknesses and varying polymeric molecular weights. It is shown that solar cells made from low molecular weight PCDTBT exhibit Langevin recombination, whereas suppressed (non-Langevin) recombination is found in solar cells made with high molecular weight PCDTBT.

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Section: Introductionmentioning

confidence: 99%

Molecular weight dependent bimolecular recombination in organic solar cells

Philippa

Stolterfoht

White

et al. 2014

The Journal of Chemical Physics

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“…9 Furthermore, it was demonstrated that the bimolecular recombination processes in conjugated polymers is correctly described by the Langevin expression. 10 However, the major difference between a pristine semiconductor and a blend is that in the latter the electrons and holes are confined to different phases, and the recombination of free electrons and holes now mainly occurs across the interface of the materials, as schematically indicated in Fig. 1͑b͒.…”

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confidence: 99%

Bimolecular recombination in polymer/fullerene bulk heterojunction solar cells

Koster

Mihailetchi

Blom

2006

Applied Physics Letters

525

515

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Bimolecular recombination in organic semiconductors is known to follow the Langevin expression, i.e., the rate of recombination depends on the sum of the mobilities of both carriers. We show that this does not hold for polymer/fullerene bulk heterojunction solar cells. The voltage dependence of the photocurrent reveals that the recombination rate in these blends is determined by the slowest charge carrier only, as a consequence of the confinement of both types of carriers to two different phases.

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“…It is easy to show that in this case the carrier lifetime becomes equal to the transit time and even equal to the dielectric relaxation time (τ = t tr = τ σ ). 16 The reason for the extracted charge being approximately equal to CU is that only charge approximately equal to CU can be transported at the time (SCLC condition: j SCLC = CU/t tr ) and while it reaches the opposite electrode the rest of charge will recombine due to the fast Langevin-type recombination in the reservoir.The following equation has been derived to experimentally estimate the relation between the charge carrier transport and recombination in high light intensity ToF, when the extracted charge Q e saturates as a function of light intensity: 16where β is the bimolecular recombination coefficient, d L is the photogeneration region (e.g. surface or volume), and β L is the Langevin recombination coefficient.…”

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confidence: 99%

A review of charge transport and recombination in polymer/fullerene organic solar cells

Pivrikas

Sariciftci

Juška

et al. 2007

Progress in Photovoltaics

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538

490

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INTRODUCTION TO CHARGE CARRIER TRANSPORT IN ORGANIC SOLAR CELLSIncreasing energy consumption and rising energy prices in the world forces to look for energy alternatives, one of the most promising being the photovoltaic solar energy conversion. Various concepts and device architectures of organic solar cells have been actively studied for more than 30 years. [1][2][3][4][5][6][7][8] Efficiencies, routinely exceeding 4-5% have been reached in thin-film organic solar cells today. From purely academic point of view, the research of organic solar cells is interesting due to novel photophysical phenomena, whereas technologically low fabrication costs due to roll-toroll printing possibilities drive the economic point of view. There are four main important processes which might limit the power conversion efficiency of photovoltaic devices: 9 1. Light absorption in the film. 2. Free charge carrier generation. 3. Charge transport to the opposite electrodes and extraction by the electrodes. 4. Carrier recombination.When the photoexcitation (an exciton) is created after the photon energy is absorbed in the material, mobile charge carriers must be created by splitting the exciton into a free electron and hole. Therefore, donor and acceptor blends are used in the organic photovoltaics to facilitate photoinduced charge transfer. If the exciton reaches the donor-acceptor interface, the electron can then be transferred to the material with lower lying Lowest Unoccupied Molecular Orbit (LUMO) if I D * − E A − Coulomb < 0, where I D * is the ionization potential of the excited donor, E A the electron affinity of the acceptor, and Coulomb summarizes all the electrostatic interactions including the exciton binding energy and all polarizations. The important parameters here are the exciton diffusion length and the distance between the donor and acceptor phases.Furthermore, both these charge carriers must be transported to the opposite electrodes and reach them prior to recombination. If after photoinduced charge transfer the electron and hole are still bound by the Coulomb potential, then typically for low mobility materials, they cannot escape from each others attraction and will finally recombine. However, the excitons can be split into free electrons and holes when the carrier dissipation distance is larger than the Coulomb radius. To fulfill this condition the Coulomb field must be screened or charge carrier hopping distance must be larger than the Coulomb radius (for low mobility materials it is unrealistic). 10 In this case mobile charge carriers can be transported to the contacts either by carrier diffusion or electric field induced drift. In order to have unity quantum efficiency for charge extraction, one needs to fulfill the condition that the charge carrier transit time t tr is much smaller than the carrier lifetime τ (t tr τ). The carrier transit time t tr = d/µE is determined by the charge carrier mobility µ, sample thickness d, and the electric field E inside the film. If the photocurrent is governed by the carrier dri...

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Langevin recombination and space-charge-perturbed current transients in regiorandom poly(3-hexylthiophene)

Cited by 74 publications

References 20 publications

Molecular weight dependent bimolecular recombination in organic solar cells

Molecular weight dependent bimolecular recombination in organic solar cells

Bimolecular recombination in polymer/fullerene bulk heterojunction solar cells

A review of charge transport and recombination in polymer/fullerene organic solar cells

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