Sgj Simon Mathijssen

Poly(diketopyrrolopyrrole-terthiophene) for ambipolar logic and photovoltaics.

A new semiconducting polymer, PDPP3T, with alternating diketopyrrolopyrrole and terthiophene units is presented. PDPP3T has a small band gap of 1.3 eV and exhibits nearly balanced hole and electron mobilities of 0.04 and 0.01 cm(2) V(-1) s(-1), respectively, in field-effect transistors (FETs). By the combination of two identical ambipolar transistors, an inverter was constructed that exhibits a gain of approximately 30. When PDPP3T was combined with [60]PCBM or [70]PCBM in a 1:2 weight ratio, photovoltaic cells were made that provide a photoresponse up to 900 nm and an AM1.5 power conversion efficiency of 3.8 or 4.7%, respectively. In contrast to the almost constant FET mobility, the efficiency of the photovoltaic cells was found to be strongly dependent on the molecular weight of PDPP3T and the use of diiodooctane as a processing agent.

Efficient Solar Cells Based on an Easily Accessible Diketopyrrolopyrrole Polymer

A new easily accessible, high molecular weight, alternating dithieno-diketopyrrolopyrrolophenylene copolymer provides high electron and hole mobilities exceeding 0.02 cm2 V-1 s-1 in FETs and AM1.5 power conversion efficiencies of 4.6% and 5.5% in solar cells when combined with [60]PCBM and [70]PCBM. The performance of the solar cells strongly depends on the use of a processing agent.

Small band gap copolymers based on furan and diketopyrrolopyrrole for field-effect transistors and photovoltaic cells

Four small band gap semiconducting copolymers based on electron deficient diketopyrrolopyrrole alternating with electron rich trimers containing furan and benzene or thiophene have been synthesized via Suzuki polymerization. The polymers have optical band gaps between 1.4 and 1.6 eV, optimized for solar energy conversion, and exhibit ambipolar charge transport in field-effect transistors with hole and electron mobilities higher than 10−2 cm2 V−1 s−1. In solar cells the polymers are used as electron donors and provide power conversion efficiencies up to 3.7% in simulated solar light when mixed with [70]PCBM as acceptor.

Small band gap polymers based on diketopyrrolopyrrole

New small band gap polymers incorporating diketopyrrolopyrrole units have been synthesized using Suzuki and Yamamoto polymerization. By alternating the electron-deficient diketopyrrolopyrrole units with different electron-rich aromatic segments, polymers were obtained with band gaps ranging from 1.24 to 1.77 eV in thin films. In field-effect transistors these polymers exhibit ambipolar charge transport with hole and electron mobilities up to 2.1 × 10−3 cm2/Vs and 1.6 × 10−4 cm2/Vs, respectively. The polymers were applied as electron donor in bulk heterojunction solar cells with [60]PCBM as electron acceptor to give a maximum power conversion efficiency of 1.7% under simulated standard solar light (AM1.5G, 100 mW/cm2). The morphology of the bulk heterojunction blend seems to limit the photovoltaic performance.

Fast ambipolar integrated circuits with poly(diketopyrrolopyrrole-terthiophene)

Ambipolar integrated circuits were prepared with poly(diketopyrrolopyrrole-terthiophene) as the semiconductor. The field-effect mobility of around 0.02 cm2/V s for both electrons and holes allowed for fabrication of functional integrated complementary metal-oxide semiconductor (CMOS)-like inverters and ring oscillators. The oscillation frequency was found to have a near quadratic dependence on the supply bias. The maximum oscillation frequency was determined to be 42 kHz, which makes this ring oscillator the fastest CMOS-like organic circuit reported to date.

Proton migration mechanism for the instability of organic field-effect transistors

During prolonged application of a gate bias, organic field-effect transistors show an instability involving a gradual shift of the threshold voltage toward the applied gate bias voltage. We propose a model for this instability in p-type transistors with a silicon-dioxide gate dielectric, based on hole-assisted production of protons in the accumulation layer and their subsequent migration into the gate dielectric. This model explains the much debated role of water and several other hitherto unexplained aspects of the instability of these transistors.

Scanning Kelvin probe microscopy on organic field-effect transistors during gate bias stress

The reliability of organic field-effect transistors is studied using both transport and scanning Kelvin probe microscopy measurements. A direct correlation between the current and potential of a p-type transistor is demonstrated. During gate bias stress, a decrease in current is observed, that is correlated with the increased curvature of the potential profile. After gate bias stress, the potential changes consistently in all operating regimes: the potential profile gets more convex, in accordance with the simultaneously observed shift in threshold voltage. The changes of the potential are attributed to positive immobile charges, which contribute to the potential, but not to the current.

Ordered Semiconducting Self-Assembled Monolayers on Polymeric Surfaces Utilized in Organic Integrated Circuits

We report on a two-dimensional highly ordered self-assembled monolayer (SAM) directly grown on a bare polymer surface. Semiconducting SAMs are utilized in field-effect transistors and combined into integrated circuits as 4-bit code generators. The driving force to form highly ordered SAMs is packing of the liquid crystalline molecules caused by the interactions between the linear alkane moieties and the pi-pi stacking of the conjugated thiophene units. The fully functional circuits demonstrate long-range order over large areas, which can be regarded as the start of flexible monolayer electronics.

On the width of the recombination zone in ambipolar organic field effect transistors

The performance of organic light emitting field effect transistors is strongly influenced by the width of the recombination zone. We present an analytical model for the recombination profile. By assuming Langevin recombination, the recombination zone width W is found to be given byW=4.34dδ, with d and δ the gate dielectric and accumulation layer thicknesses, respectively. The model compares favorably to both numerical calculations and measured surface potential profiles of an actual ambipolar device.

Anomalous current transients in organic field-effect transistors

Here we study the origin of the gate bias-stress effect in organic p-type transistors. Based on water-mediated exchange between holes in the semiconductor and protons in the gate dielectric, we predict anomalous current transients for a non-constant gate bias, while ensuring accumulation. When applying a strongly negative gate bias followed by a less negative bias a back-transfer of protons to holes and an increase of the current is expected. We verify this counterintuitive behavior experimentally and can quantitatively model the transients with the same parameters as used to describe the threshold voltage shift.