Suppressing the environmental dependence of the open‐circuit voltage in inverted polymer solar cells through a radical polymer anodic modifier

Rostro, Lizbeth; Galicia, Lucio; Boudouris, Bryan W.

doi:10.1002/polb.23640

Cited by 31 publications

(25 citation statements)

References 47 publications

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“…Moreover, the PTMA thin film stacks were irradiated with solar light and the effects on the electrical properties were monitored. Specifically, while the use of PTMA as an anodic interfacial modifier in inverted geometry OPV devices has been demonstrated, the effect that sustained illumination exposure has on the PTMA layer itself was not evaluated. For example, light irradiation can catalyze the oxidation between oxygen and the conjugated thiophene ring on the backbone of poly(3‐hexylthiophene) .…”

Section: Resultsmentioning

confidence: 99%

On the Environmental and Electrical Bias Stability of Radical Polymer Conductors in the Solid State

Baradwaj

Rostro

Boudouris

2015

Macro Chemistry & Physics

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Radical polymers are emerging as a promising class of electronically active macromolecules for solid‐state organic electronic applications due to their synthetic flexibility and scalability; however, the electrical and chemical stability of radical polymer thin films has yet to be established. Here, it is demonstrated that the model radical polymer, poly(2,2,6,6‐tetramethylpiperidinyloxy methacrylate) (PTMA), shows excellent solid‐state electrochemical stability when exposed to both bias stressing and varying amounts of moisture in the environment. Specifically, PTMA thin films show consistent performance when continuously swept across a variety of voltage ranges. Furthermore, PTMA remains stable when exposed to a constantly applied bias for 20 h. These two key results demonstrate the stability of the open‐shell repeat unit and the reversibility of the chemical oxidation–reduction (redox) reaction that facilitates charge transport. Additionally, PTMA thin films that are exposed to a range of relative humidity values for 2 h retained consistent electronic performance before and after humidity exposure. This highlights that exposure to water vapor does not decrease the robustness associated with the nitroxide radical. These results establish the stoutness associated with radical polymers and highlight the potential for radical polymers to be implemented in a number of advanced organic electronic technologies.

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Section: Resultsmentioning

confidence: 99%

On the Environmental and Electrical Bias Stability of Radical Polymer Conductors in the Solid State

Baradwaj

Rostro

Boudouris

2015

Macro Chemistry & Physics

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“…There have been other recent studies where other polymer acids and radical polymers have been used in place of PEDOT:PSS, but in these cases device effi ciencies have not been improved relative to devices with PEDOT:PSS HTLs, though Nafi on, in particular, has been shown to improve device lifetime. [ 15,32,33 ] …”

Section: Introductionmentioning

confidence: 99%

Doped Interlayers for Improved Selectivity in Bulk Heterojunction Organic Photovoltaic Devices

Mauger

Glasser

Villers

et al. 2015

Adv Materials Inter

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can be inserted between the active layer and the contact layer to create a new interface with more favorable properties, which is the method explored here. These thin layers are often called interlayers and many types of materials have been investigated, such as low work-function metals, [ 3,4 ] metal salts, [ 5 ] silane-based selfassembled monolayers (SAMs), [ 6 ] phosphonic-acid SAMs, [ 7,8 ] metal oxides, [9][10][11] polymers, [12][13][14][15] and polyelectrolytes. [ 16 ] Other examples are also available in the literature, with a thorough review provided by Ma et al. [ 1 ] The majority of these interlayers improve device performance by reducing electronic barriers for extraction of the desired charge carrier and/or increasing charge selectivity by blocking the undesired charge carrier. Creating interfaces or layers that preferentially extract only one polarity of charge carrier are key to optimizing BHJ devices since the intermixed donor and acceptor do not create a diode.Charge selective layers create a thermodynamic barrier for collection of the undesired carrier (electron or hole). The effects of selective layers on OPV diode characteristics in the dark and under illumination are distinct from changes due to shifts in the contact layer work function ( φ ).[ 17 ] Changes in φ tend to only manifest themselves in the open-circuit voltage ( V oc ), whereas changes in selectivity from thermodynamic barriers (with constant φ ) are evident in the reverse saturation current and shunt resistance, in addition to V oc . Additionally, a study comparing injection and extraction effi ciency in OPV devices with and without selective contacts showed that the dominant mechanism controlling V oc is injection, with charge selective contacts having a much lower rate of charge injection into the active layer. [ 18 ] One of the most commonly used charge selective contact layers in OPV devices is the polymer blend poly(3,4-ethylenedi oxythiophene):poly(styrene sulfonate) (PEDOT:PSS). The nanostructure of PEDOT:PSS layers is complex due to the phase-separated colloidal structure of the PEDOT:PSS ink. In the bulk of the layer, elongated ellipsoids of PEDOT are surrounded by thin shells of PSS. [ 19,20 ] This morphology gives rise to its anisotropic conductivity and refractive index. [ 21,22 ] However, the surface of the PEDOT:PSS has a 3-4 nm thick PSS-rich surface layer. [23][24][25] This PSS-rich layer forms due to surface energy considerations. In blend fi lms, the component with the lowest surface energy

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“…It is postulated that, in the presence of an electric field, adjacent radical sites will undergo electron transfer with one another if there is a sufficiently high density of radical sites present within the film to allow for electrochemical reaction to propagate from one electrode to the other . This mechanism has allowed radical polymers to be implemented in non‐volatile memory devices, diodes, and as an interfacial modifying layer in solar cells . It is critical to note that these electronic applications are only possible due to the open‐shell moiety, and the chemistry of the radical unit plays a crucial role in the transport and stability properties of the materials .…”

Section: Radical Polymersmentioning

confidence: 99%

Recent advances in the syntheses of radical-containing macromolecules

Wingate

Boudouris

2016

J. Polym. Sci. Part A: Polym. Chem.

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Tailor-made polymers containing specific chemical functionalities have ushered in a number of emerging fields in polymer science. In most of these next-generation applications the focus of the community has centered upon closed-shell macromolecules. Conversely, macromolecules containing stable radical sites have been less studied despite the promise of this evolving class of polymers. In particular, radical-containing macromolecules have shown great potential in magnetic, energy storage, and biomedical applications. Here, the progress regarding the syntheses of open-shell containing polymers are reviewed in two distinct subclasses. In the first, the syntheses of radical polymers (i.e., materials composed of nonconjugated macromolecular backbones and with open-shell units present on the polymer pendant sites) are described. In the second, polyradical (i.e., macromolecules containing stabi-lized radical sites either within the macromolecular backbone or those containing radical sites that are stabilized through a large degree of conjugation) synthetic schemes are presented. Thus, the state-of-the-art in open-shell macromolecular syntheses will be reported and future means by which to advance the current archetype will be discussed. By detailing the synthetic pathways possible for, and the inherent synthetic limitations of, the creation of these functional polymers, the community will be able to extend the bounds of the radical-containing macromolecular paradigm.

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Suppressing the environmental dependence of the open‐circuit voltage in inverted polymer solar cells through a radical polymer anodic modifier

Cited by 31 publications

References 47 publications

On the Environmental and Electrical Bias Stability of Radical Polymer Conductors in the Solid State

On the Environmental and Electrical Bias Stability of Radical Polymer Conductors in the Solid State

Doped Interlayers for Improved Selectivity in Bulk Heterojunction Organic Photovoltaic Devices

Recent advances in the syntheses of radical-containing macromolecules

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