Correlating the effective work function at buried organic/metal interfaces with organic solar cell characteristics

Shamieh, Basel; Anselmo, Ana Sofia; Vogel, Uwe; Lariou, Eirini; Hayes, Sophia C.; Koch, Norbert; Frey, Gitti L.

doi:10.1039/c8tc02381f

Cited by 10 publications

(7 citation statements)

References 44 publications

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“…Work function is by definition a surface property and the EWF at interfaces depends on the electrochemical and electrical properties of the interfacing materials, and the chemical and physical interactions between them . Hence, work function values measured for bare metal surfaces or even distinctly prepared additive/metal interfaces do not necessarily reflect the energy level alignment at the organic/metal buried interface . Moreover, specific processing condition employed to fabricate the sample for direct energy level study may differ from those adopted for actual device fabrication .…”

Section: Resultsmentioning

confidence: 99%

Tuning Contact Resistance in Top‐Contact p‐Type and n‐Type Organic Field Effect Transistors by Self‐Generated Interlayers

Sarkar

Shamieh

Verbeek

et al. 2019

Adv Funct Materials

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(1 of 9)combined with inherent mechanical flexi bility. [1] Accordingly, extensive research efforts are invested in the development of protocols suitable for flexible device fabrication, rolltoroll processing, and printing, [2] and the design and synthesis of high performance materials, specifi cally high mobility semiconductors, [3] gate insulators, [4] and printable conductors. [5] Importantly, because charge injection, extraction, and accumulation occur at the interfaces of different materials, new solution processing methodologies that control the structure and composition of interfaces in OFETs are also essential for high performances. [6] One seminal inter facial electronic process that limits OFET performances is inefficient charge car rier injection from the source electrode to the organic semiconducting channel. Efficient injection into the organic semiconductor requires Ohmic con tacts, i.e., barrierless energy level align ment at the organic/metal interface. [6a,7] The Schottky barriers, and associated contact resistance, can be reduced by aligning either the highest occupied molecular orbital (HOMO) of a ptype organic semicon ductor or the lowest unoccupied molecular orbital (LUMO) of an ntype organic semiconductor, with the work function of the metal electrode. Therefore, tuning the work function of the metal electrode is a practical approach for optimizing charge injection/extraction and hence device performance. [8] A wellestablished strategy to tune the effective work function (EWF) at the organic/metal interface is by introducing ultrathin organic or inorganic interlayers between the metal contact and the organic semiconductor. [9] In case of organic interlayer, polar molecules are placed at the semiconductor/metal interface and modify the EWF by imposing a dipole at the interface. The energy level alignment can be controllably tuned through the chemical composition of the molecule and the direction and magnitude of the dipole. [7,10] The most common techniques of depositing organic interlayers onto substrates are thermal deposition [11] and spin coating from orthogonal solvents. [12] Another wellknown technique is to deposit selfassembled monolayers (SAM) by immersing the substrate with metal electrodes in the SAM solution prior to the semiconductor Contact resistance significantly limits the performance of organic field-effect transistors (OFETs). Positioning interlayers at the metal/organic interface can tune the effective work-function and reduce contact resistance. Myriad techniques offer interlayer processing onto the metal pads in bottom-contactOFETs. However, most methods are not suitable for deposition on organic films and incompatible with top-contact OFET architectures. Here, a simple and versatile methodology is demonstrated for interlayer processing in both p-and n-type devices that is also suitable for top-contact OFETs. In this approach, judiciously selected interlayer molecules are co-deposited as additives in the semiconducting polymer active layer. During top contact dep...

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Section: Resultsmentioning

confidence: 99%

Tuning Contact Resistance in Top‐Contact p‐Type and n‐Type Organic Field Effect Transistors by Self‐Generated Interlayers

Sarkar

Shamieh

Verbeek

et al. 2019

Adv Funct Materials

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“…Thus, OPVs with BIPO and TIPO interfacial materials exhibited drastic increases in all photovoltaic parameters, as expected. The higher V oc values of OPVs with interfacial layers, compared to those of OPVs with Al-only cathodes, are attributable to the increased work function differences between the anodes and cathodes. − The work function of the cathode decreased on introduction of an interfacial layer; the difference between the effective work functions of the anode and cathode thus increased. The increased V oc values of OPVs with interfacial layers support the results of the UPS measurements discussed above.…”

Section: Resultsmentioning

confidence: 99%

A Solution-Processed Cathode Interfacial Layer Facilitates Efficient Energy Level Alignment in Organic Photovoltaics

et al. 2021

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We synthesized and used small-molecule cathode interfacial materials in organic photovoltaic devices (OPVs). Two small-molecule interfacial materials with phosphine oxide and benzoimidazole groups induced strong interface dipoles and chelated with the metal electrodes. The molecules can be dissolved in various organic solvents for processing. We used isopropanol (an environmentally benign solvent) to dissolve the small-molecule materials and spin-coated solutions onto photoactive layers. The materials formed ohmic contacts between the electron acceptor PC71BM and the Al cathodes and facilitated efficient charge carrier extraction at the electrodes of OPVs. Analyses of the material and device properties of the two interfacial materials and the photovoltaic performances of OPVs with the materials revealed that the materials were promising cathode interfacial materials for photovoltaic applications. The interfacial material featuring two benzoimidazole groups optimally formed smooth interfacial layers affording better energy level alignment between the electron acceptors and the cathode.

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“…For example, we recently showed that interlayers composed of two molecules, one that effectively reduces the barrier for electron injection and the second that effectively reduces the barrier for hole injection, perfectly balance ambipolar OFET performance. 14,18,19 Deposition of such interlayers requires judicious materials selection and sensitive tuning and processing of the distinct interlayers, which inflict significant complications on device manufacturing and cost effectiveness. Therefore, it is necessary to develop a practical and simple solution for barrierless injection of both electrons and holes from one type of electrode into an organic semiconductor film.…”

Section: Introductionmentioning

confidence: 99%

Universal electrode for ambipolar charge injection in organic electronic devices

et al. 2022

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Correlating the effective work function at buried organic/metal interfaces with organic solar cell characteristics

Abstract: Self-generated interlayers provide insight on the energy level alignment at the organic semiconductor/back contact interface in organic solar cells.

Cited by 10 publications

References 44 publications

Tuning Contact Resistance in Top‐Contact p‐Type and n‐Type Organic Field Effect Transistors by Self‐Generated Interlayers

Tuning Contact Resistance in Top‐Contact p‐Type and n‐Type Organic Field Effect Transistors by Self‐Generated Interlayers

A Solution-Processed Cathode Interfacial Layer Facilitates Efficient Energy Level Alignment in Organic Photovoltaics

Universal electrode for ambipolar charge injection in organic electronic devices

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