Understanding S-shaped current-voltage characteristics of organic solar cells: Direct measurement of potential distributions by scanning Kelvin probe

Saive, Rebecca; Mueller, Christian; Schinke, Janusz; Lovrinčić, Robert; Kowalsky, Wolfgang

doi:10.1063/1.4846615

Cited by 27 publications

(22 citation statements)

References 14 publications

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“…Similar interface effects were also described as the cause for s-shaped I-V curves by Glatthaar et al [109], and the importance of the electrodes was investigated by Jin et al [110]. In a direct microscopic measurement, it was possible to visualize the described charge barrier in P3HT:PCBM solar cells [3]. In this measurement, a scanning electron microscopy/focused ion beam system was combined with a scanning probe system [111] to perform in-situ cross section preparation and measurement [112].…”

Section: S-shaped I-v Curves In Organic Solar Cellsmentioning

confidence: 73%

“…Although, macroscopic device properties of organic solar cells resemble the ones of their inorganic cousins, there have been extensive debates on the origin of the photovoltage [88]- [91] and on charge carrier transport mechanisms [92]- [94]. S-shaped I-V curves have also been commonly observed in organic solar cells [3], [91], [95]- [106], and several studies have attempted to explain the occurrence within the frame work of organic semiconductor charge transport [3], [91], [100], [102], [107].…”

Section: S-shaped I-v Curves In Organic Solar Cellsmentioning

confidence: 99%

“…One of the most thoroughly studied material systems in the organic photovoltaic community are poly(3-hexylthiophene): [6], [6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) solar cells. S-shaped I-V curves have frequently been observed [2], [3], [95], [105]. Kumar et al managed to tune the position of the I-V curve kink in P3HT:PCBM solar cells by introducing Bathocuprine (BCP) and V 2 O 5 at the charge extraction interfaces [95].…”

Section: S-shaped I-v Curves In Organic Solar Cellsmentioning

confidence: 99%

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S-Shaped Current–Voltage Characteristics in Solar Cells: A Review

Saive

2019

IEEE J. Photovoltaics

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S-shaped current-voltage (I-V) characteristics are a frequently occurring hurdle in the development of new solar cell material combinations and device architectures. Their presence points to the existence of a charge transport bottleneck that needs to be removed in order to unlock high fill factors and power conversion efficiencies. In this review, examples of studies in which s-shaped I-V curves have appeared are presented, and the cause and mitigation are discussed. Different solar cell material systems are often treated by separate communities, thereby, also the physics of s-shaped I-V curves have been treated separately. This review covers the main solar cell technologies-silicon, thin film, organic, hybrid-with the aim to provide an overarching picture of the common mechanisms and universal guidelines for mitigation of s-shaped I-V characteristics in emerging solar cell technologies. Except for a few studies on organic solar cells, s-shaped I-V curves are reported to result from charge transport barriers at one of the (selective) contact layers that can be overcome by interface engineering and doping.Index Terms-Current-voltage characteristics, s-shape, roll over.

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Section: S-shaped I-v Curves In Organic Solar Cellsmentioning

confidence: 73%

Section: S-shaped I-v Curves In Organic Solar Cellsmentioning

confidence: 99%

Section: S-shaped I-v Curves In Organic Solar Cellsmentioning

confidence: 99%

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S-Shaped Current–Voltage Characteristics in Solar Cells: A Review

Saive

2019

IEEE J. Photovoltaics

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“…The origins of S-kinks are usually considered to be due to at least one of the following: i) interfacial dipoles or defects, ii) charge carrier mobility imbalance and iii) energy barriers. 87,[141][142][143][144][145] The equivalent circuit model based on elementary circuit elements is used to understand the loss mechanisms that influence the FF at low PFI concentrations. In the present study, these losses are largely related to the series (R S ) and shunt (R SH ) resistances, as the composition and morphology of the active layer, and the temperature are unchanged.…”

Section: Rectification Of Opvsmentioning

confidence: 99%

Influence of perfluorinated ionomer in PEDOT:PSS on the rectification and degradation of organic photovoltaic cells

et al. 2018

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Poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is widely used to build optoelectronic devices. However, as a hygroscopic waterbased acidic material, it brings major concerns for stability and degradation, resulting in an intense effort to replace it in organic photovoltaic (OPV) devices. In this work, we focus on the perfluorinated ionomer (PFI) polymeric additive to PEDOT:PSS. We demonstrate that it can reduce the relative amplitude of OPV device burn-in, and find two distinct regimes of influence. At low concentrations there is a subtle effect on wetting and work function, for instance, with a detrimental impact on the device characteristics, and above a threshold it changes the electronic and device properties. The abrupt threshold in the conducting polymer occurs for PFI concentrations greater than or equal to the PSS concentration and was revealed by monitoring variations in transmission, topography, work-function, wettability and OPV device characteristics. Below this PFI concentration threshold, the power conversion efficiency (PCE) of OPVs based on poly(3-hexylthiophene-2,5-diyl):[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) are impaired largely by low fill-factors due to poor charge extraction. Above the PFI concentration threshold, we recover the PCE before it is improved beyond the pristine PEDOT:PSS layer based OPV devices. Supplementary to the performance enhancement, PFI improves OPV device stability and lifetime. Our degradation study leads to the conclusion that PFI prevents water from diffusing to and from the hygrosopic PEDOT:PSS layer, which slows down the deterioration of the PEDOT:PSS layer and the aluminum electrode. These findings reveal mechanisms and opportunities that should be taken into consideration when developing components to inhibit OPV degradation. 35-38 whilst oxidation, delamination and interfacial effects may occur at the electrodes. 39-45 Metal ion diffusion from the electrodes and changes in morphology have also been reported in both the active and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) layers. C. T. Howells et al. 2/14organic optoelectronics between indium tin oxide (ITO) anodes and active layers. [54][55][56][57] With its metal properties, 58-62 PEDOT:PSS and similar conducting layers are part of the contact and are sometimes called hole injection layers in light emitting devices. By analogy, in this solar cell work, PEDOT:PSS is then referred to as a hole extraction layer (HEL) rather than a hole transport layer or interlayer. The large ionisation potential promotes an Ohmic contact and improves the built-in electric field, whilst high conductivity and transparency ensure minimal resistive and optical losses, respectively. 53,63,64 The HEL also helps to prevent metal ion diffusion from the ITO into the active layer and the cathode from short-circuiting the anode. 50 The PSS is a water-soluble polyelectrolyte that serves as a charge balancing dopant during the polymerisation of EDOT monomers. It oxidises and stabi...

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“…Furthermore, we observe a substantial charge carrier extraction barrier and hence S-shaped I-V curve, which is a wellknown phenomena that can be attributed to accumulated space charges at the material interfaces or a non-ideal Ohmic contact. [61][62][63][64] This observation can be explained by the nonoptimized metal semiconductor interfaces, which are likely to induce recombination-active trap states and accumulated space charges. We note that the photocurrent under the AM 1.5G spectrum was below the detection limit ($1 pA) of the source measure unit used and therefore did not allow the measurement of our devices under the full solar spectrum.…”

Section: -26mentioning

confidence: 99%

Au-Cu2O core-shell nanowire photovoltaics

Oener

Mann

Sciacca

et al. 2015

Applied Physics Letters

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Semiconductor nanowires are among the most promising candidates for next generation photovoltaics. This is due to their outstanding optical and electrical properties which provide large optical cross sections while simultaneously decoupling the photon absorption and charge carrier extraction length scales. These effects relax the requirements for both the minority carrier diffusion length and the amount of semiconductor needed. Metal-semiconductor core-shell nanowires have previously been predicted to show even better optical absorption than solid semiconductor nanowires and offer the additional advantage of a local metal core contact. Here, we fabricate and analyze such a geometry using a single Au-Cu2O core-shell nanowire photovoltaic cell as a model system. Spatially resolved photocurrent maps reveal that although the minority carrier diffusion length in the Cu2O shell is less than 1 μm, the radial contact geometry with the incorporated metal electrode still allows for photogenerated carrier collection along an entire nanowire. Current-voltage measurements yield an open-circuit voltage of 600 mV under laser illumination and a dark diode turn-on voltage of 1 V. This study suggests the metal-semiconductor core-shell nanowire concept could be extended to low-cost, large-scale photovoltaic devices, utilizing for example, metal nanowire electrode grids coated with epitaxially grown semiconductor shells.

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Understanding S-shaped current-voltage characteristics of organic solar cells: Direct measurement of potential distributions by scanning Kelvin probe

Cited by 27 publications

References 14 publications

S-Shaped Current–Voltage Characteristics in Solar Cells: A Review

S-Shaped Current–Voltage Characteristics in Solar Cells: A Review

Influence of perfluorinated ionomer in PEDOT:PSS on the rectification and degradation of organic photovoltaic cells

Au-Cu2O core-shell nanowire photovoltaics

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