Mamatimin Abbas

Balanced charge carrier mobilities in bulk heterojunction organic solar cells

All solution processed ambipolar bulk heterojunction organic field effect transistors were fabricated using Au and Al as hole and electron injection contacts to study both types of charge carrier mobilities in a single device. Poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) were mixed with different ratios. Well balanced electron and hole mobilities were obtained at 1:0.3 ratio. Organic solar cells with the same ratio yielded draft enhancement in device performance parameters, indicating optimized carrier transport in the bulk of solar cell devices.

Application of non-metal doped titania for inverted polymer solar cells

Inverted bulk-heterojunction polymer solar cells have been fabricated applying non-metal doped TiO2 as electron extraction buffer layers. Spin-coated films from nitrogen, sulphur, and iodine doped TiO2 nanoparticles dispersed in dimethyl sulphoxide showed comparable roughness and uniformity as those from the pure TiO2 nanoparticles. The highest power conversion efficiency (PCE) of 1.67% was obtained for N-doped TiO2, whereas in the case of pure TiO2, PCE was around 1%. The highest short circuit current density (Jsc = 10.66 mA cm−2) was achieved for I-doped TiO2. Moreover, it was observed that devices with doped TiO2 exhibit better stability under constant illumination comparing to the control devices with pure TiO2.

Piezoelectric polymer gated OFET: Cutting-edge electro-mechanical transducer for organic MEMS-based sensors

The growth of micro electro-mechanical system (MEMS) based sensors on the electronic market is forecast to be invigorated soon by the development of a new branch of MEMS-based sensors made of organic materials. Organic MEMS have the potential to revolutionize sensor products due to their light weight, low-cost and mechanical flexibility. However, their sensitivity and stability in comparison to inorganic MEMS-based sensors have been the major concerns. In the present work, an organic MEMS sensor with a cutting-edge electro-mechanical transducer based on an active organic field effect transistor (OFET) has been demonstrated. Using poly(vinylidenefluoride/trifluoroethylene) (P(VDF-TrFE)) piezoelectric polymer as active gate dielectric in the transistor mounted on a polymeric micro-cantilever, unique electro-mechanical properties were observed. Such an advanced scheme enables highly efficient integrated electro-mechanical transduction for physical and chemical sensing applications. Record relative sensitivity over 600 in the low strain regime (<0.3%) was demonstrated, which represents a key-step for the development of highly sensitive all organic MEMS-based sensors.

Control of carrier mobilities for performance enhancement of anthracene-based polymer solar cells

High performance organic solar cells were realized using an anthracene-based polymer. Charge carrier mobilities of both electrons and holes in solvent annealed polymer and fullerene derivative mixtures were studied using organic field-effect transistors. Fine tuning of donor to acceptor ratios revealed optimum conditions for balanced mobilities, which led to a high power conversion efficiency (PCE) of 4.02% in the organic solar cells. A methanol wash approach further enhanced the PCE to 4.65%. This work demonstrates the importance of carrier transport control in optimizing the performance of polymer solar cells.

A Multifunctional Interlayer for Solution Processed High Performance Indium Oxide Transistors

Multiple functionality of tungsten polyoxometalate (POM) has been achieved applying it as interfacial layer for solution processed high performance In2O3 thin film transistors, which results in overall improvement of device performance. This approach not only reduces off-current of the device by more than two orders of magnitude, but also leads to a threshold voltage reduction, as well as significantly enhances the mobility through facilitated charge injection from the electrode to the active layer. Such a mechanism has been elucidated through morphological and spectroscopic studies.

Giant electro-mechanical transduction in all-organic MEMS for physical and chemical sensors

This paper reports an organic MEMS sensor with a cutting-edge electro-mechanical transducer based on an active organic field effect transistor (OFET). The strategy lies in the integration of a piezoelectric Poly (VinyliDene Fluoride/TriFluoroEthylene) (P(VDF/TrFE)) copolymer as active gate dielectric layer in an OFET device mounted on a polymer micro-cantilever. The charges generated by the piezoelectric layer due to surface strain are converted and amplified into drain current. Such an advanced scheme enables highly efficient integrated electromechanical transduction with record relative sensitivity ((ΔID/IDS)/ε) over 600 in the low strain regime, constituting a key-step for the development of highly sensitive MEMS sensors.

Synthesis and photovoltaic properties of a new donor-acceptor conjugated polymer based on fluorinated benzothiadiazole units

A novel fluorinated copolymer (PDTSffBT) based on dithienosilole donor unit and fluorinated benzothiadiazole acceptor unit has been synthesized for polymer solar cells. This copolymer exhibits a deeper HOMO energy level compared to that of hydrogenated benzothiadiazole-based copolymer (PDTSBT), resulting in high open-circuit voltages well exceeding 0.75 V. The introduction of the two electron-withdrawing fluorine atoms on the benzothiadiazole unit also leads to an increase in the molar extinction coefficient as well as the interchain interaction in the PDTSffBT copolymer with respect to its analogue PDTSBT copolymer. Power conversion efficiency (PCE) of the device using PDTSffBT:PC71BM as active layer (2.93 %) is much higher than of a PDTSBT:PC71BM (1.64 %) counterpart under identical conditions.