Post-processing treatment of conductive polymers to enhance electrical conductivity

A method for enhancing electrical conductivity of a film which includes at least one conductive polymer. The method includes providing the film comprising the at least one conductive polymer and at least one polymer acid, agitating the film in at least one reagent; and, placing the film on a heated surface. The at least one reagent includes a reagent acid that is stronger than the polymer acid. The conductivity of the treated film is significantly greater than the conductivity of the untreated film.Board of Regents, University of Texas Syste

Ligand chemistry of titania precursor affects transient photovoltaic behavior in inverted organic solar cells

The chemistry of the precursor from which charge transport layers are formed can significantly affect the device performance of organic solar cells. Here, we compare two common precursors that are used to generate titania electron transport layers and elucidate their effects on the transient characteristics of inverted bulk-heterojunction polymer solar cells comprising poly(3-hexyl hiophene) and [6,6]-phenyl-C-61-butyric acid methyl ester. Substituting the isopropyl ligands of titanium isopropoxide with 2-methoxyethanol leads to electron transport layers that require a shorter illumination time to fill shallow electron traps. Furthermore, organic solar cells with titania electron transport layers prepared with such pre-modified titania precursor exhibit higher power-conversion efficiencies stemming from lower trap densities. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4795287open4

Semiconducting SWNTs sorted by polymer wrapping:How pure are they?

Short-channel field-effect transistors (FETs) prepared from semiconducting single-walled carbon nanotube (s-SWNT) dispersions sorted with poly(2,5-dimethylidynenitrilo-3,4-didodecylthienylene) are demonstrated. Electrical analysis of the FETs shows no evidence of metallic tubes out of a total number of 646 SWNTs tested, implying an estimated purity of our semiconducting SWNT solution higher than 99.85%. These findings confirm the effectiveness of the polymer-wrapping technique in selecting semiconducting SWNTs, as well as the potential of sorted nanotubes for the fabrication of short channel FETs comprising from 1 to up to 15 nanotubes without inter-nanotube junctions. Published by AIP Publishing

Numerical analysis with experimental verification to predict outdoor power conversion efficiency of inverted organic solar devices

Inverted organic solar cell (IOSC) devices with different volume ratios of In₂S₃ nanoparticles have been studied under local spectral irradiances in Malaysia with respect to that of AM1.5G. The J-V curves of encapsulated IOSC devices were measured outdoor using an Ivium Potentiostat and local spectral irradiances were acquired using an AVANTES spectrometer concurrently. All of the IOSC devices experienced significant improvement in power conversion efficiency (PCE) under the both local sunny and cloudy conditions with respect to the AM 1.5G, by 22–35% and 31–65%, respectively. From spectral analysis, the area under the graph of spectral irradiance in UV–visible region is significantly higher compared to infrared region for both local sunny and cloudy conditions, by 44.6% and 55.9%, respectively, while it is only recorded as 12.9% for AM 1.5G. Last but not the least, we have successfully verified the numerical analysis to predict device performance by comparing the simulated and measured PCE values for different irradiance intensities whereby the prediction of PCE is better under sunny condition with a deviation of 3.4–10.8% compared to cloudy conditions, with deviation of 28.9–30.5%

Striking the Right Balance of Intermolecular Coupling for High-Efficiency Singlet Fission

Singlet fission is a process that splits collective excitations, or excitons, into two with unity efficiency. This exciton splitting process, unique to molecular photophysics, has the potential to considerably improve the efficiency of optoelectronic devices through more efficient light harvesting. While the first step of singlet fission has been characterized in great detail, subsequent steps critical to achieving overall highly-efficient singlet-to-triplet conversion are only just beginning to become well understood. One of the most elementary suggestions, which has yet to be tested, is that an appropriately balanced coupling is necessary to ensure overall highly efficient singlet fission; that is, the coupling needs to be strong enough so that the first step is fast and efficient, yet weak enough to ensure the independent behavior of the resultant triplets. In this work, we show how high overall singlet-to-triplet conversion efficiencies can be achieved in singlet fission by ensuring that the triplets comprising the triplet pair behave as independently as possible. We show that side chain sterics govern local packing in amorphous pentacene derivative nanoparticles, and that this in turn controls both the rate at which triplet pairs form and the rate at which they decay. We show how compact side chains and stronger couplings promote a triplet pair that effectively couples to the ground state, whereas bulkier side chains promote a triplet pair that appears more like two independent and long-lived triplet excitations. Our results show that the triplet pair is not emissive, that its decay is best viewed as internal conversion rather than triplet–triplet annihilation, and perhaps most critically that, in contrast to a number of recent suggestions, the triplets comprising the initially formed triplet pair cannot be considered independently. This work represents a significant step toward better understanding intermediates in singlet fission, and how molecular packing and couplings govern overall triplet yields

Computationally Aided Design of a High-Performance Organic Semiconductor: The Development of a Universal Crystal Engineering Core

Herein, we describe the design and synthesis of a suite of molecules based on a benzodithiophene “universal crystal engineering core”. After computationally screening derivatives, a trialkylsilylethyne-based crystal engineering strategy was employed to tailor the crystal packing for use as the active material in an organic field-effect transistor. Electronic structure calculations were undertaken to reveal derivatives that exhibit exceptional potential for high-efficiency hole transport. The promising theoretical properties are reflected in the preliminary device results, with the computationally optimized material showing simple solution processing, enhanced stability, and a maximum hole mobility of 1.6 cm2 V−1 s−1

Polymer Crystallization in 25 nm Spheres

Crystallization within the discrete spheres of a block copolymer mesophase was studied by time-resolved x-ray scattering. The cubic packing of microdomains, established by self-assembly in the melt, is preserved throughout crystallization by strong interblock segregation even though the amorphous matrix block is well above its glass transition temperature. Homogeneous nucleation within each sphere yields isothermal crystallizations which follow first-order kinetics, contrasting with the sigmoidal kinetics normally exhibited in the quiescent crystallization of bulk polymers.Comment: accepted for publication in Physical Review Letters, 2/28/2000; scheduled for 5/1/2000 issu

Molecular helices as electron acceptors in high-performance bulk heterojunction solar cells

Despite numerous organic semiconducting materials synthesized for organic photovoltaics in the past decade, fullerenes are widely used as electron acceptors in highly efficient bulk-heterojunction solar cells. None of the non-fullerene bulk heterojunction solar cells have achieved efficiencies as high as fullerene-based solar cells. Design principles for fullerene-free acceptors remain unclear in the field. Here we report examples of helical molecular semiconductors as electron acceptors that are on par with fullerene derivatives in efficient solar cells. We achieved an 8.3% power conversion efficiency in a solar cell, which is a record high for non-fullerene bulk heterojunctions. Femtosecond transient absorption spectroscopy revealed both electron and hole transfer processes at the donor−acceptor interfaces. Atomic force microscopy reveals a mesh-like network of acceptors with pores that are tens of nanometres in diameter for efficient exciton separation and charge transport. This study describes a new motif for designing highly efficient acceptors for organic solar cells