Organic semiconductors are emerging as a viable alternative to amorphous silicon in a range of thin‐film transistor devices. With the possibility to formulate these p‐type materials as inks and ...subsequently print into patterned devices, organic‐based transistors offer significant commercial advantages for manufacture, with initial applications such as low performance displays and simple logic being envisaged. Previous limitations of both air stability and electrical performance are now being overcome with a range of both small molecule and polymer‐based solution‐processable materials, which achieve charge carrier mobilities in excess of 0.5 cm2 V−1 s−1, a benchmark value for amorphous silicon semiconductors. Polymer semiconductors based on thienothiophene copolymers have achieved amongst the highest charge carrier mobilities in solution‐processed transistor devices. In this Progress Report, we evaluate the advances and limitations of this class of polymer in transistor devices.
Thienothiophene semiconducting polymers can exhibit a planar backbone conformation, leading to highly crystalline structures, often with good orientation and inter‐grain alignment. This thin‐film microstructure is optimal in achieving high charge‐carrier mobilities in organic field‐effect transistors.
A polyanionic electrolyte is used as gate insulator in top‐gate p‐channel polymer thin‐film transistors. The high capacitance of the polyelectrolyte film allows the transistors and integrated ...circuits to operate below 1.5 V. Seven‐stage ring oscillators that operate at supply voltages down to 0.9 V and exhibit signal propagation delays as low as 300 µs per stage are reported.
The impact of side-chain variations on the photothermal stability of solar cells containing poly(benzodithiophene-diketopyrrolopyrrole) polymers are investigated in the absence of oxygen. Four ...different side-chains of benzodithiophene (BDT) are synthesized and copolymerized with diketopyrrolopyrrole (DPP) by Stille polymerization. The photothermal stability is measured as active layer blends with phenyl-C61-butyric acid methyl ester (PCBM) in encapsulated inverted photovoltaic cell architecture with zinc oxide and
PSS as transport layers (ITO/ZnO/active layer/
PSS/Ag). Device degradation is correlated to the morphological behavior of the polymer:blend upon AM1.5 illumination (UV-visible light, 50 °C) and have been investigated by AFM, XRD, and UV-Vis. Once exposed to the light and to the temperature the BHJ stability is governed by two processes (i) PCBM crystallization and (ii) PCBM dimerization. Dimerization results in a rapid initial performance decrease followed by a more gradual decrease caused by a slower thermally activated crystallization. Depending on the blend morphology, dictated by the polymer's alkyl chain, the two processes occur to different extents thereby modulating the BHJ stability. Thus, of the polymer side-chains explored, linear alkyl side-chains stabilized the bulk heterojunction most effectively followed by no side-chain, alkoxy and branched side-chains. Lowering the concentration of fullerene in the active layer also reduces the rate of degradation across the polymers tested. This is a result of both the rate of crystallization and dimerization of fullerene being dependent on its concentration and the nature of the polymer side-chains. This approach appears to be a general strategy to increase the polymer:PCBM stability.
The synthesis of three novel thiophene-based conjugated molecules (1−3) is presented. We report the electronic and redox properties of these compounds along with the corresponding electrochemically ...prepared polymers. The structures of compounds 1 and 2 have been confirmed by single-crystal X-ray diffraction studies. Noncovalent S···O interactions in 1 act to hold the molecule in a planar conformation and this is in stark contrast to the twisted nature of the 3,4-ethylenedithiothiophene (EDTT) analogue. The degree of planarity within the molecules dictates the effective conjugation length within the materials and also the packing of the molecules in the solid state. CGL-TOF studies give hole mobilities up to 4 × 10−5 cm2 V−1 s−1 for compound 1 and 1.5 × 10−5 cm2 V−1 s−1 for 2.
We have used particle induced X-ray emission analysis and particle induced gamma-ray emission analysis to determine the elemental impurity concentrations in ...poly(2,5-bis(3-decylthiophen-2-yl)thieno2,3-bthiophene samples that have undergone different washing and extraction procedures to remove impurities. Field-effect transistors (FETs) were fabricated from the materials and their electrical characteristics show no significant differences between the devices made from different material samples. Reducing the metal residue levels below the ones measured in the starting material (300
mg/kg Fe, 7
mg/kg Zn, 3000
mg/kg Pd and 12000
mg/kg Sn) does not improve the FET performance. This suggests that it is not necessary to completely remove metal residues in the polymer for FET applications.
The Positive Reinforcement Opportunity Project (PROP) was a pilot program developed to build on the efficacy of contingency management (CM) using positive reinforcement to address the treatment needs ...of gay and bisexual men currently using crystal methamphetamines (meth). It was hypothesized that a version of CM could be implemented in San Francisco that was less costly than traditional treatment methods and reached gay and other MSM using meth who also engaged in highrisk sexual activity. Of the 178 men who participated in PROP from December 2003 to December 2005, many self-reported behaviors for acquiring and spreading sexually transmitted diseases including HIV infection. During the initial intake, 73% reported high-risk sexual behavior in the prior three months, with 60% reporting anal receptive and/or insertive sex without condoms. This report describes the implementation of PROP and suggest both its limitations and potential strengths. Initial findings suggest that PROP was a useful and low cost substance use treatment option that resulted in a 35% 90-day completion rate, which is similar to graduation rates from traditional, more costly treatment options. Further evaluation of the limited data from three- and six-month follow-up of those who completed PROP is currently ongoing.
The Positive Reinforcement Opportunity Project (PROP) was a pilot program developed to build on the efficacy of contingency management (CM) using positive reinforcement to address the treatment needs ...of gay and bisexual men currently using crystal methamphetamines (meth). It was hypothesized that a version of CM could be implemented in San Francisco that was less costly than traditional treatment methods and reached gay and other MSM using meth who also engaged in high-risk sexual activity. Of the 178 men who participated in PROPfrom December 2003 to December 2005, many self-reported behaviors for acquiring and spreading sexually transmitted diseases including HIV infection. During the initial intake, 73% reported high-risk sexual behavior in the prior three months, with 60% reporting anal receptive and/or insertive sex without condoms. This report describes the implementation of PROP and suggest both its limitations and potential strengths. Initial findings suggest that PROP was a useful and low cost substance use treatment option that resulted in a 35% 90-day completion rate, which is similar to graduation rates from traditional, more costly treatment options. Further evaluation of the limited data from three- and six-month follow-up of those who completed PROP is currently ongoing.
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