Organic semiconductor

About: Organic semiconductor is a research topic. Over the lifetime, 15905 publications have been published within this topic receiving 533881 citations.

Universal strategy for Ohmic hole injection into organic semiconductors with high ionization energies.

Abstract: Barrier-free (Ohmic) contacts are a key requirement for efficient organic optoelectronic devices, such as organic light-emitting diodes, solar cells, and field-effect transistors. Here, we propose a simple and robust way of forming an Ohmic hole contact on organic semiconductors with a high ionization energy (IE). The injected hole current from high-work-function metal-oxide electrodes is improved by more than an order of magnitude by using an interlayer for which the sole requirement is that it has a higher IE than the organic semiconductor. Insertion of the interlayer results in electrostatic decoupling of the electrode from the semiconductor and realignment of the Fermi level with the IE of the organic semiconductor. The Ohmic-contact formation is illustrated for a number of material combinations and solves the problem of hole injection into organic semiconductors with a high IE of up to 6 eV. It is shown that Ohmic contacts for the injection of hole carriers into organic semiconductors with high ionization energy can be formed by adding ultrathin interlayers with higher ionization energy.

Scaling behavior and parasitic series resistance in disordered organic field-effect transistors

Abstract: The scaling behavior of the transfer characteristics of solution-processed disordered organic thin-film transistors with channel length is investigated. This is done for a variety of organic semiconductors in combination with gold injecting electrodes. From the channel-length dependence of the transistor resistance in the conducting ON-state, we determine the field-effect mobility and the parasitic series resistance. The extracted parasitic resistance, typically in the MΩ range, depends on the applied gate voltage, and we find experimentally that the parasitic resistance decreases with increasing field-effect mobility.

Hysteresis of pentacene thin-film transistors and inverters with cross-linked poly(4-vinylphenol) gate dielectrics

Abstract: The authors report the effects of hydroxyl groups (OH bonds) on the electrical reliabilities of pentacene organic thin-film transistors (OTFTs) with poly-4-vinylphenol (PVP) gate dielectrics. PVP gate dielectric films mixed with different concentrations of methylated poly(melamine-co-formaldehyde) (MMF) were fabricated, and experiments on the hysteresis behavior of the OTFT device were conducted. Pentacene TFTs with the PVP (MMF 0wt.%) exhibited a large hysteresis, while in the PVP (MMF 125wt.%), nearly no hysteresis was observed. Large hysteresis observed in OTFT devices was confirmed to be strongly related to the hydroxyl groups existing inside of the polymeric dielectrics and could reduced by the decrease of OH group.

Large n- and p-type thermoelectric power factors from doped semiconducting single-walled carbon nanotube thin films

Abstract: Lightweight, robust, and flexible single-walled carbon nanotube (SWCNT) materials can be processed inexpensively using solution-based techniques, similar to other organic semiconductors. In contrast to many semiconducting polymers, semiconducting SWCNTs (s-SWCNTs) represent unique one-dimensional organic semiconductors with chemical and physical properties that facilitate equivalent transport of electrons and holes. These factors have driven increasing attention to employing s-SWCNTs for electronic and energy harvesting applications, including thermoelectric (TE) generators. Here we demonstrate a combination of ink chemistry, solid-state polymer removal, and charge-transfer doping strategies that enable unprecedented n-type and p-type TE power factors, in the range of 700 μW m−1 K−2 at 298 K for the same solution-processed highly enriched thin films containing 100% s-SWCNTs. We also demonstrate that the thermal conductivity appears to decrease with decreasing s-SWCNT diameter, leading to a peak material zT ≈ 0.12 for s-SWCNTs with diameters in the range of 1.0 nm. Our results indicate that the TE performance of s-SWCNT-only material systems is approaching that of traditional inorganic semiconductors, paving the way for these materials to be used as the primary components for efficient, all-organic TE generators.

Co(III) Complexes as p-Dopants in Solid-State Dye-Sensitized Solar Cells

Abstract: Following our recent work on the use of Co(III) complexes as p-type dopants for triarylamine-based organic hole-conductors, we herein report on two new Co(III) complexes for doping applications. With the aim of ameliorating the dopant’s suitability for its use in solid-state dye-sensitized solar cells, we show how the properties of the dopant can be easily adjusted by a slight modification of the molecular structure. We prove the eligibility of the two new dopants by characterizing their optical and electrochemical properties and give evidence that both of them can be used to oxidize the molecular hole-transporter spiro-MeOTAD. Finally, we fabricate high-performance solid-state dye-sensitized solar cells using a state-of-the-art metal-free organic sensitizer in order to elucidate the influence of the type of dopant on device performance.