Charge extraction with linearly increasing voltage: A numerical model for parameter extraction

Neukom, Martin; Reinke, Nils A.; Ruhstaller, Beat

doi:10.1016/j.solener.2011.02.028

Cited by 59 publications

(50 citation statements)

References 8 publications

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“…37 The electrical transient and impedance measurements reported here have been performed by the all-in-one characterization platform Paios developed and commercialized by Fluxim AG, Switzerland. 39 Drift-diffusion simulations to calculate the CELIV currents and charge density profiles have been generated using the commercial tool Setfos 4.4 by Fluxim AG, 40 which was already successfully used to characterize OSCs 23,30,41 and OLEDs. 38,42 Hereby, the macroscopic polarization was taken into account as demonstrated in our previous publication.…”

Section: Methodsmentioning

confidence: 99%

“…The application of this formula is, however, very limited, as the underlying assumptions (drift only, uniform charge carrier distribution, no RC-effects) are usually not justified. 23 Several other approaches have therefore been pursued to describe the full transient current, and specifically to quantify the mobility. [24][25][26][27] In bipolar devices, the peak consists of both electrons and holes, and it is not possible to unambiguously assign the extracted mobility to one specific charge carrier type.…”

Section: Introductionmentioning

confidence: 99%

“…Also, depending on the ratio of the electron and hole mobility as well as the ratio of electron and hole density the extracted mobility can be the faster one, the slower one or an average of the two species. Finally, the peak position and thereby the extracted mobility depend on the relation of the peak height j max to the displacement current plateau j 0 , the employed voltage ramp rate, (bipolar) recombination, and the external series resistance 23,25 which further complicates the analysis and can render simple analytical formulas inaccurate. There have been adaptions and extensions to the initial equation, but also these are approximations and valid only in specific cases.…”

Section: Introductionmentioning

confidence: 99%

“…28 The most general modelling approach for the bipolar case still is the dual-carrier drift-diffusion model, ideally coupled with a fitting routine, which in the end allows for a real quantitative extraction of both charge carrier mobilities. 23,29,30 II. APPROACH So far, it seemed impossible to use fully operating bipolar devices for a valid CELIV analysis.…”

Section: Introductionmentioning

confidence: 99%

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The use of charge extraction by linearly increasing voltage in polar organic light-emitting diodes

Züfle

Altazin

Hofmann

et al. 2017

Journal of Applied Physics

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We demonstrate the application of the CELIV (charge carrier extraction by linearly increasing voltage) technique to bilayer organic light-emitting devices (OLEDs) in order to selectively determine the hole mobility in N,N0-bis(1-naphthyl)-N,N0-diphenyl-1,10-biphenyl-4,40-diamine (α-NPD). In the CELIV technique, mobile charges in the active layer are extracted by applying a negative voltage ramp, leading to a peak superimposed to the measured displacement current whose temporal position is related to the charge carrier mobility. In fully operating devices, however, bipolar carrier transport and recombination complicate the analysis of CELIV transients as well as the assignment of the extracted mobility value to one charge carrier species. This has motivated a new approach of fabricating dedicated metal-insulator-semiconductor (MIS) devices, where the extraction current contains signatures of only one charge carrier type. In this work, we show that the MIS-CELIV concept can be employed in bilayer polar OLEDs as well, which are easy to fabricate using most common electron transport layers (ETLs), like Tris-(8-hydroxyquinoline)aluminum (Alq3). Due to the macroscopic polarization of the ETL, holes are already injected into the hole transport layer below the built-in voltage and accumulate at the internal interface with the ETL. This way, by a standard CELIV experiment only holes will be extracted, allowing us to determine their mobility. The approach can be established as a powerful way of selectively measuring charge mobilities in new materials in a standard device configuration.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

The use of charge extraction by linearly increasing voltage in polar organic light-emitting diodes

Züfle

Altazin

Hofmann

et al. 2017

Journal of Applied Physics

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“…The simulations are based on a standard one-dimensional driftdiffusion-recombination solver [138,139] assuming a negligible amount of equilibrium carriers, which is typically the case in organic semiconductors [52] as well as in the studied devices. For simulations of dispersive transport, we implemented a multiple trapping and release model [124,125,140] with an exponential density of localized states.…”

Section: Numerical Simulationsmentioning

confidence: 99%

Charge Generation and Transport Phenomena in Disordered Organic Semiconductors and Photovoltaic Diodes

Stolterfoht¹

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Organic semiconductors are of great interest for a broad range of optoelectronic applications due to their solution processability, chemical tunability and mechanical flexibility. In contrast to traditional banded semiconductors, organic semiconductors are intrinsically disordered systems and exhibit therefore much lower charge carrier mobilities. They are also low dielectric constant systems -as such, their photo-excitations are excitonic at room temperature with the electron-hole pair remaining Coulombically-bound. Blending organic semiconductors with differing electron affinities, so-called electron acceptors and donors, creates molecular heterojunctions which deliver the required driving force for exciton separation. These so-called bulk heterojunctions (BHJs) are the dominant architecture for creating organic photovoltaic cells and photodetectors. However, not least because of an incomplete understanding of the underlying physical mechanism that control the conversion of photons to free charges, and the subsequent extraction of these free charges to the electrodes, these organic optoelectronic systems still lag behind their inorganic counterparts.Motivated by these factors, the work described in this thesis advances the fundamental understanding of the loss mechanisms associated with charge photogeneration and charge transport phenomena in BHJ organic solar cells and photodetectors, and presents new experimental methodologies to study these processes. The transport of photogenerated charge carriers in the percolated donor: acceptor pathways towards the extracting electrodes has been studied in-depth via existing and newly developed transient photovoltage and steady-state characterization techniques. A simple but conclusive understanding has been developed which allows for minimization of the detrimental recombination of free charge carriers for given device parameters such as film thickness, applied voltage and the mobility of the slower carrier type (either electrons or holes). The models' predictions have been experimentally validated for many different (> 25) BHJ solar cell systems. Inspired by the need to selectively optimize the processes which control the photocurrent output of the cell, such a charge photogeneration and extraction, a technique to quantify and disentangle both efficiencies has been developed as a next step. Corroborated by transient absorption spectroscopy, the dynamics of the photocarrier generation process was examined. The results suggest that the so-called charge-transfer state (CTS) separation limits the conversion of photons to free charges and the photocurrent output from short-circuit to the maximum power point, strongly depending on the slower carrier ii mobility. These findings were explained by the ability of the slower carriers to leave the donor: acceptor interface via 1) a high enough mobility, 2) a sufficiently large domain size, and 3) enough conduction pathways (entropy). This work also shows that the dynamics of charge extraction and CTS dissociation are simi...

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Charge Extraction by Linearly Increasing Voltage (CELIV) Method for Investigation of Charge Carrier Transport and Recombination in Disordered Materials

Grynko

Juška

Reznik

2022

Photoconductivity and Photoconductive Materials

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Charge extraction with linearly increasing voltage: A numerical model for parameter extraction

Cited by 59 publications

References 8 publications

The use of charge extraction by linearly increasing voltage in polar organic light-emitting diodes

The use of charge extraction by linearly increasing voltage in polar organic light-emitting diodes

Charge Generation and Transport Phenomena in Disordered Organic Semiconductors and Photovoltaic Diodes

Charge Extraction by Linearly Increasing Voltage (CELIV) Method for Investigation of Charge Carrier Transport and Recombination in Disordered Materials

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