Interface Doping for Ohmic Organic Semiconductor Contacts Using Self‐Aligned Polyelectrolyte Counterion Monolayer

Seah, W.K.H.; Tang, Cindy G.; Png, Rui‐Qi; Keerthi, Venu; Zhao, Chao; Guo, Han; Yang, Jiayi; Zhou, Mi; Ho, Peter K. H.; Chua, Lay‐Lay

doi:10.1002/adfm.201606291

Cited by 27 publications

(17 citation statements)

References 51 publications

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“…The results reveal that the two features above are preserved. Incidentally, this justifies the assumption of identical source and drain contact resistivities in organic field-effect transistors with symmetrical contacts 44 , 45 . To obtain the theoretical dependence of ρ c on ϕ and σ G , we stepped FL through the DOS tail, evaluating electrode ϕ at each step and taking into account the carrier density accumulated at the contact (Supplementary Note 2 ).…”

Section: Resultssupporting

confidence: 53%

“…Since this contact is unchanged, the strong ϕ dependence of ρ c ( J ) can directly be attributed to the hole contact. For ϕ ≳ 5.15 eV, ρ c ( J ) shows little dependence on J , a non-dispersive behavior found also for notionally ohmic contacts in organic field-effect transistors 44 , 45 . Near ϕ pin however, ρ c ( J ) exhibits an apparent inverse power law dependence, with exponent of –0.67, between the two limits.…”

Section: Resultsmentioning

confidence: 69%

“…Although particularly important for solar cells, which are highly sensitive to the resulting series resistance, the clarification here of the ohmic transition closes a key gap in our understanding of disordered semiconductor contacts, pointing to a simple rule for the design of contacts relevant also to injection diodes and field-effect transistors. The development of heavily doped contacts, whether imposed by charge-counterbalancing polyelectrolyte monolayers 45 , or the use of self-compensated, heavily doped polymer injection layers 50 , is thus key to realizing ohmic contacts at will.…”

Section: Resultsmentioning

confidence: 99%

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Ohmic transition at contacts key to maximizing fill factor and performance of organic solar cells

et al. 2018

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While thermodynamic detailed balance limits the maximum power conversion efficiency of a solar cell, the quality of its contacts can further limit the actual efficiency. The criteria for good contacts to organic semiconductors, however, are not well understood. Here, by tuning the work function of poly(3,4-ethylenedioxythiophene) hole collection layers in fine steps across the Fermi-level pinning threshold of the model photoactive layer, poly(3-hexylthiophene):phenyl-C61-butyrate methyl ester, in organic solar cells, we obtain direct evidence for a non-ohmic to ohmic transition at the hole contact that lies 0.3 eV beyond its Fermi-level pinning transition. This second transition corresponds to reduction of the photocurrent extraction resistance below the bulk resistance of the cell. Current detailed balance analysis reveals that this extraction resistance is the counterpart of injection resistance, and the measured characteristics are manifestations of charge carrier hopping across the interface. Achieving ohmic transition at both contacts is key to maximizing fill factor without compromising open-circuit voltage nor short-circuit current of the solar cell.

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Section: Resultssupporting

confidence: 53%

Section: Resultsmentioning

confidence: 69%

Section: Resultsmentioning

confidence: 99%

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Ohmic transition at contacts key to maximizing fill factor and performance of organic solar cells

et al. 2018

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“…[ 129 ] In the community of OFET, the insertion of self‐assembled monolayer or transition metal oxide between the source/drain and organic semiconductor has been shown to improve the charge injection and extraction process. [ 130–135 ] Nuzzo et al demonstrated a graphene‐passivated nickel electrode which can be used as an efficient hole injector. [ 136 ]…”

Section: Charge Injection At Electrode–organic Interfacementioning

confidence: 99%

Interface Engineering in Organic Electronics: Energy‐Level Alignment and Charge Transport

2020

Small Science

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Organic light‐emitting diodes (OLEDs) and organic solar cells are new members of trillion‐dollar semiconductor industry. The structure of these devices generally consists of a stack of several organic layers sandwiched between two electrodes. The electronic processes such as the energy‐level alignment at and charge transport across these interfaces play a key role to the overall performance of the organic devices. Thus, interface physics is important for design and engineering of organic devices. Herein, recent progress in energy‐level alignment at and charge transport across organic interfaces is reviewed. In addition, basic material physics of organic semiconductors such as energy levels, energy disorder, and molecular orientation is introduced. Recent progress in theories and experiments on energy‐level alignment at and charge transport across molecular heterojunctions is then discussed. Case studies of applying interface physics for guiding fabrication of ideal devices are also provided.

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“…When using doped polymers to modify Au electrodes, the ambipolar behaviors of a D–A conjugated polymer, poly(2,5‐bis(alkyl)‐1,4‐dioxopyrrolo[3,4‐c]pyrrole‐3,6‐diyl‐thiophene‐2,5‐diylthieno[2,3‐b]thiophene‐2,5‐diyl‐thiophene‐2,5‐diyl) (DPPT2‐T), could be transformed into those of p‐ or n‐FETs, alternatively (Figure e,f). Seah et al used a polyelectrolyte counterion monolayer as the interlayer to dope the contact interface and achieved Ohmic contacts with contact resistivities in the range of 0.1–1 Ω cm 2 . With a self‐aligned polyelectrolyte counterion interlayer, an enhancement in performance could be realized for both p‐ and n‐type OFETs.…”

Section: Binary Interfaces In Functional Devicesmentioning

confidence: 99%

Precise Control of Interfacial Charge Transport for Building Functional Optoelectronic Devices

Zhang

Chen

Guo

2019

Adv Materials Technologies

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studies have not only improved device performance, but have even built novel functions. At present, interface engineering has become a research hotspot and has great potential for further applications in diverse fields, ranging from integrated circuits and energy conversion to catalysis and chemical/biosensors. Scientists with various backgrounds have been devoting great efforts to this area, which has moved from the simple improvement of device performance to branch out in broad directions, indicating its interdisciplinarity.As shown in Figure 1c, an important interface for an FET is the semiconductor/ electrode interface, which typically determines the efficiency of charge carrier injection and extraction. In general, the charge injection of a metal/organic semiconductor (OSC) junction can be described in terms of thermal electron emission or tunneling mechanisms, depending on the concentration of defect states inside the bandgap (Figure 1c, left and middle). [1] By carefully selecting the self-assembled monolayer (SAM) or thin buffer interlayer to modify the metal electrode (Figure 1c, right), the interface charge injection barrier can be fine-tuned, thereby significantly reducing the contact resistance of the device. More interestingly, by using a stimuli-responsive conformational isomer as a functional layer to modify the electrode interface, functionalization of the electrodes can be achieved. This concept laid the foundation for the construction of functional devices such as optical/electrical switches, memory, and photodetectors.The semiconductor/dielectric interface is another important interface in FETs, that governs carrier transport (Figure 1d, left), because generation, transport, and regulation of charge carriers all occur in the first few layers (<10 nm) of semiconductors at the interface (Figure 1d, middle). In addition, the modification of the dielectric surface has been shown to help reduce the defects, improve the roughness, change the polarity, and modulate the surface hydrophilic/hydrophobic properties. These changes further affect the transport of carriers at the semiconductor/dielectric interface (Figure 1d, right) and have a significant impact on the morphology of the semiconductor layer. Furthermore, modification of the interface with SAMs or stimuli-responsive layers offers an important and general methodology to improve device performance and even integrate new molecular functionalities, such as photocontrollable memory, superconductivity, and charge-trap memory, into organic electrical circuits. Optoelectronic devices and interfaces therein have captured great attention in both scientific and industrial communities because of the wide variety of their unique properties. From a materials chemistry point of view, each layer and individual component of an optoelectronic device possesses the possibility of flexible chemical modification, making it feasible to dope, mix, and physically/chemically modify the interface. Exploiting the novel properties in optoelectronic devices with diverse la...

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Interface Doping for Ohmic Organic Semiconductor Contacts Using Self‐Aligned Polyelectrolyte Counterion Monolayer

Cited by 27 publications

References 51 publications

Ohmic transition at contacts key to maximizing fill factor and performance of organic solar cells

Ohmic transition at contacts key to maximizing fill factor and performance of organic solar cells

Interface Engineering in Organic Electronics: Energy‐Level Alignment and Charge Transport

Precise Control of Interfacial Charge Transport for Building Functional Optoelectronic Devices

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