Relating Frontier Orbital Energies from Voltammetry and Photoelectron Spectroscopy to the Open‐Circuit Voltage of Organic Solar Cells

Willems, R.E.M.; Weijtens, Christ H. L.; Vries, Xander de; Coehoorn, R.; Janssen, Raj René

doi:10.1002/aenm.201803677

Cited by 77 publications

(98 citation statements)

References 64 publications

(173 reference statements)

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“…We fit the experimental dark current densities using E g,fit , σ int,h , and A i ,fit as fitting parameters (Table ). The E g,fit values match very well to the expected E g , within the experimental error of the UPS data (≈0.1 eV) . We found that when σ int was set equal to σ b , the experimental activation barriers would not be reproduced correctly.…”

Section: Jd R and Eqe Of Bhj Opds Measured At V = −2 V At Photon Ensupporting

confidence: 64%

“…Ultraviolet Photoelectron Spectroscopy : The UPS measurements were performed according to recently published methods and are further detailed in the Supporting Information.…”

Section: Methodsmentioning

confidence: 99%

“…Since J d and V oc are measured under entirely different illumination and voltage bias conditions, this correlation is intriguing. The V oc of BHJ photovoltaic devices is known to vary linearly with the energy difference between the acceptor LUMO and donor HOMO, here referred to as the effective bandgap ( E g ). Indeed, we find that the V oc depends linearly on E g , with slope of the linear fit equal to 1 (Figure S5, Supporting Information).…”

Section: Jd R and Eqe Of Bhj Opds Measured At V = −2 V At Photon Enmentioning

confidence: 99%

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On the Origin of Dark Current in Organic Photodiodes

Simone

Dyson

Weijtens

et al. 2019

Advanced Optical Materials

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110

138

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Minimizing the reverse bias dark current while retaining external quantum efficiency is crucial if the light detection sensitivity of organic photodiodes (OPDs) is to compete with inorganic photodetectors. However, a quantitative relationship between the magnitude of the dark current density under reverse bias ( Jd) and the properties of the bulk heterojunction (BHJ) active layer has so far not been established. Here, a systematic analysis of Jd in state‐of‐the‐art BHJ OPDs using five polymers with a range of energy levels and charge transport characteristics is presented. The magnitude and activation energy of Jd are explained using a model that assumes charge injection from the metal contacts into an energetically disordered semiconductor. By relating Jd to material parameters, insights into the origin of Jd are obtained that enable the future selection of successful OPD materials.

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Section: Jd R and Eqe Of Bhj Opds Measured At V = −2 V At Photon Ensupporting

confidence: 64%

“…Ultraviolet Photoelectron Spectroscopy : The UPS measurements were performed according to recently published methods and are further detailed in the Supporting Information.…”

Section: Methodsmentioning

confidence: 99%

Section: Jd R and Eqe Of Bhj Opds Measured At V = −2 V At Photon Enmentioning

confidence: 99%

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On the Origin of Dark Current in Organic Photodiodes

Simone

Dyson

Weijtens

et al. 2019

Advanced Optical Materials

Self Cite

110

138

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“…One explanation for this discrepancy lies in the experimental uncertainty in determining LUMO A and HOMO D , as their absolute value can depend on the measurement technique . As an example, the HOMO energy of PCDTBT was reported to be −5.5 or −5.4 eV .…”

Section: Why Does the Experimental Jd Deviate From Its Intrinsic Limit?mentioning

confidence: 99%

“…As an example, the HOMO energy of PCDTBT was reported to be −5.5 or −5.4 eV . Furthermore, reported LUMO energies of fullerene acceptors range between −4.3 and −3.8 eV . While these uncertainties might affect the results in Figure b, they would not explain deviations from the J d empirical limits by several orders of magnitude.…”

Section: Why Does the Experimental Jd Deviate From Its Intrinsic Limit?mentioning

confidence: 99%

Organic Photodetectors and their Application in Large Area and Flexible Image Sensors: The Role of Dark Current

Simone

Dyson

Meskers

et al. 2019

Adv Funct Materials

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291

357

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Organic photodetectors (OPDs) have gained increasing interest as they offer cost-effective fabrication methods using low temperature processes, making them particularly attractive for large area image detectors on lightweight flexible plastic substrates. Moreover, their photophysical and optoelectronic properties can be tuned both at a material and device level. Visible-light OPDs are proposed for use in indirect-conversion X-ray detectors, fingerprint scanners, and intelligent surfaces for gesture recognition. Near-infrared OPDs find applications in biomedical imaging and optical communications. For most applications, minimizing the OPD dark current density (J d ) is crucial to improve important figures of merits such as the signal-to-noise ratio, the linear dynamic range, and the specific detectivity (D*). Here, a quantitative analysis of the intrinsic dark current processes shows that charge injection from the electrodes is the dominant contribution to J d in OPDs. J d reduction is typically addressed by fine-tuning the active layer energetics and stratification or by using charge blocking layers. Yet, most experimental J d values are higher than the calculated intrinsic limit. Possible reasons for this deviation are discussed, including extrinsic defects in the photoactive layer and the presence of trap states. This provides the reader with guidelines to improve the OPD performances in view of imaging applications.

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Mapping the Density of States Distribution of Organic Semiconductors by Employing Energy Resolved–Electrochemical Impedance Spectroscopy

Bäßler

Kroh

Schauer

et al. 2020

Adv Funct Materials

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Although the density of states (DOS) distribution of charge transporting states in an organic semiconductor is vital for device operation, its experimental assessment is not at all straightforward. In this work, the technique of energy resolved–electrochemical impedance spectroscopy (ER‐EIS) is employed to determine the DOS distributions of valence (highest occupied molecular orbital (HOMO)) as well as electron (lowest unoccupied molecular orbital (LUMO)) states in several organic semiconductors in the form of neat and blended films. In all cases, the core of the inferred DOS distributions are Gaussians that sometimes carry low energy tails. A comparison of the HOMO and LUMO DOS of P3HT inferred from ER‐EIS and photoemission (PE) or inverse PE (IPE) spectroscopy indicates that the PE/IPE spectra are by a factor of 2–3 broader than the ER‐EIS spectra, implying that they overestimate the width of the distributions. A comparison of neat films of MeLPPP and SF‐PDI2 or PC(61)BM with corresponding blends reveals an increased width of the DOS in the blends. The results demonstrate that this technique does not only allow mapping the DOS distributions over five orders of magnitude and over a wide energy window of 7 eV, but can also delineate changes that occur upon blending.

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Relating Frontier Orbital Energies from Voltammetry and Photoelectron Spectroscopy to the Open‐Circuit Voltage of Organic Solar Cells

Cited by 77 publications

References 64 publications

On the Origin of Dark Current in Organic Photodiodes

On the Origin of Dark Current in Organic Photodiodes

Organic Photodetectors and their Application in Large Area and Flexible Image Sensors: The Role of Dark Current

Mapping the Density of States Distribution of Organic Semiconductors by Employing Energy Resolved–Electrochemical Impedance Spectroscopy

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