We report the synthesis, characterization, solution-phase assembly of nanowires, field-effect charge transport, and photovoltaic properties of regioregular poly(3-pentylthiophene) (P3PT), the first ...regioregular poly(3-alkylthiophene) with an odd-numbered alkyl side chain length to be so investigated. Two samples of P3PT with weight-average molecular weights of 61 800 and 77 000 and 1.4−1.5 polydispersity index have comparable solubility and processability in organic solvents as regioregular poly(3-hexylthiophene) (P3HT) but have a higher melting transition at 259 °C. X-ray diffraction of P3PT films revealed a lamellar structure with an interlayer d 100 spacing of 1.51 nm and a π-stacking d 010 spacing of 0.374 nm, both smaller than in P3HT. Crystalline nanowires of 16−17 nm width and aspect ratios as high as 465 were assembled from P3PT solution. Field-effect transistors fabricated from P3PT thin films showed a mobility of holes of up to 0.10 cm2/(V s), and the carrier mobility increased with molecular weight. Bulk heterojunction solar cells based on P3PT/fullerene (PC71BM) blend thin films had a power conversion efficiency of 3.70% under 100 mW/cm2 AM1.5 solar illumination in air and a maximum external quantum efficiency of 69%. Similarly illuminated solar cells based on nanocomposites of P3PT nanowires/PC71BM had a 3.33% power conversion efficiency. These results demonstrate that P3PT is an attractive polymer semiconductor suitable for applications in thin-film and nanowire-based field-effect transistors and bulk heterojunction solar cells.
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Understanding the influence of polymer molecular weight on the morphology, photophysics, and photovoltaic properties of polymer solar cells is central to further advances in the design, processing, ...performance and optimization of the materials and devices for large scale applications. We have synthesized six number-average molecular weight (
M
n
) values (21-127 kDa) of biselenophene-naphthalenediimide copolymer (
PNDIBS
)
via
direct heteroarylation polymerization and used them to investigate the effects of the acceptor polymer molecular weight on the charge transport, blend photophysics, blend morphology, and photovoltaic properties of all-polymer solar cells (all-PSCs) based on
PNDIBS
and the donor polymer
PBDB-T
. The short-circuit current and power conversion efficiency (PCE) of the
PBDB-T
:
PNDIBS
blend devices were found to increase with increasing
M
n
until reaching peaks at an optimal molecular weight of 55 kDa and then decreased with further increases in
M
n
. The maximum PCE of 10.2% observed at the optimal
M
n
value of 55 kDa coincided with optimal blend charge transport properties, blend photophysics, and blend morphology at this critical molecular weight. Compared to the bi-continuous network of ∼5.5-6.5 nm crystalline domains with predominantly
face-on
molecular orientations observed at 55 kDa, a relatively disordered microstructure with larger scale phase separation was evident at higher
M
n
while more finely packed crystalline domains were seen at 21 kDa. The sensitivity of the device efficiency to the active layer thickness was found to also depend on the
PNDIBS
M
n
value. These results highlight the importance of tuning the molecular weight of the polymer components to optimize the morphology, charge transport, photophysics and efficiency of all-polymer solar cells. The results also provide new insights on structure-property relationships for a promising n-type semiconducting copolymer.
This work provides a unified understanding on how polymer molecular weight influences the blend photophysics, blend morphology, charge transport, and photovoltaic properties of all-polymer solar cells.
The solution-phase self-assembly of nanowires (NWs) from diblock copolymer semiconductors, poly(3-butylthiophene)-block-poly(3-octylthiophene), of different block compositions gave crystalline NWs of ...similar width (13−16 nm) but a tunable average aspect ratio (length/width) of 50−260. The power conversion efficiency of bulk heterojunction solar cells comprising the diblock copolythiophene NWs and PC71BM was found to increase with increasing aspect ratio, reaching 3.4% at the highest average aspect ratio of 260. The space charge limited current mobility of holes in neat films of the copolymer NWs and in copolymer NWs/PC71BM films (∼1.0 × 10−4 cm2/(V s)) was invariant with aspect ratio, reflecting the parallel orientation of the NWs to the substrate. The enhancement of photovoltaic efficiency with increasing aspect ratio of NWs was explained in terms of increased exciton and charge photogeneration and collection in the bulk heterojunction solar cells.
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New donor–acceptor copolymers incorporating both a strong electron-accepting diketopyrrolopyrrole unit and a weak electron-deficient thiazolothiazole or benzobisthiazole moiety were synthesized, ...characterized, and found to exhibit very high charge carrier mobility. Stille coupling copolymerization gave copolymers having moderate number-average molecular weights of 17.0–18.5 kDa with polydispersities of 3.3–4.0 and optical band gaps of 1.22–1.38 eV. High performance p-channel field-effect transistors were obtained using the thiazolothiazole-linked copolymers, PDPTT and PDPTTOx, giving hole mobilities of 0.5 and 1.2 cm2/(V s), respectively, with on/off current ratios of 105 to 106. In contrast, the benzobisthiazole-linked copolymer PDPBT had a substantially lower field-effect mobility of holes (0.005 cm2/(V s)) due to its amorphous solid state morphology. Bulk heterojunction solar cells fabricated by using one of the thiazolothiazole-linked copolymer, PDPTT, as electron donor and PC71BM acceptor show a power conversion efficiency of 3.4% under 100 mW/cm2 AM1.5 irradiation in air.
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46.
Introducing organic nanowire transistors Briseno, Alejandro L.; Mannsfeld, Stefan C.B.; Jenekhe, Samson A. ...
Materials today,
April 2008, 2008-04-00, 20080401, Volume:
11, Issue:
4
Journal Article
Peer reviewed
Open access
Organic nanowires self-assembled from small-molecule semiconductors and conducting polymers have attracted an enormous amount of interest for use in organic field-effect transistors. This new class ...of materials offers solution processability, the potential for elucidating transport mechanisms and structure-property relationships, and the realization of high-performance transistors that rival the performance of amorphous Si. We discuss the self-assembly of one-dimensional, single-crystalline organic nanowires, show the structures of commonly employed organic semiconductors, and review some of the advances in this field.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Electrospun nanofibers of two series of binary blends of poly2-methoxy-5-(2-ethylhexoxy)-1,4-phenylenevinylene (MEH−PPV) with regioregular poly(3-hexylthiophene) (PHT) and with ...poly(9,9-dioctylfluorene) (PFO) were prepared, and their morphology and optical and electrical properties were characterized. Morphological and photophysical studies showed that the phase-separated domains in MEH−PPV/PHT nanofibers (30−50 nm) are much smaller as compared to blend thin films (100−150 nm), and efficient energy transfer was observed in these blend nanofibers. The MEH−PPV/PFO blend nanofibers had cocontinuous or core−shell structures, and significant energy transfer was absent in these blend nanofibers as compared to bulk thin films. Field-effect transistors based on MEH−PPV/PHT blend nanofibers showed exponential dependence of hole mobility on blend composition. The hole mobility decreased from 1 × 10-4 cm2/(V s) in 20 wt % MEH−PPV blend nanofibers to 5 × 10-6 cm2/(V s) at 70 wt %. If corrected for the reduced channel area of the transistors, the effective hole mobility varies from 5 × 10-5 to 1 × 10-3 cm2/(V s) and is similar to that of spin-coated blend thin films. Our results demonstrate that electrospun nanofibers of binary blends of conjugated polymers have tunable, composition-dependent, optical, and electronic properties that can be exploited in field-effect transistors.
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Hierarchical materials that exhibit order over multiple length scales are ubiquitous in nature. Because hierarchy gives rise to unique properties and functions, many have sought inspiration from ...nature when designing and fabricating hierarchical matter. More and more, however, nature’s own high-information content building blocks, proteins, peptides, and peptidomimetics, are being coopted to build hierarchy because the information that determines structure, function, and interfacial interactions can be readily encoded in these versatile macromolecules. Here, we take stock of recent progress in the rational design and characterization of hierarchical materials produced from high-information content blocks with a focus on stimuli-responsive and “smart” architectures. We also review advances in the use of computational simulations and data-driven predictions to shed light on how the side chain chemistry and conformational flexibility of macromolecular blocks drive the emergence of order and the acquisition of hierarchy and also on how ionic, solvent, and surface effects influence the outcomes of assembly. Continued progress in the above areas will ultimately usher in an era where an understanding of designed interactions, surface effects, and solution conditions can be harnessed to achieve predictive materials synthesis across scale and drive emergent phenomena in the self-assembly and reconfiguration of high-information content building blocks.
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We report the synthesis of two barbiturate end-capped non-fullerene acceptors and demonstrate their efficient function in high voltage output organic solar cells. The acceptor with the lower LUMO ...level is shown to exhibit suppressed geminate recombination losses, resulting in enhanced photocurrent generation and higher overall device efficiency.
n-Type conjugated polymers based on naphthalene diimide (NDI) and various selenophene derivatives have been synthesized, characterized and evaluated as semiconductors for n-channel organic ...field-effect transistors (OFETs). The new poly(naphthalene diimides) (PNDIs) have weight average molecular weights of 12-107 kDa with a polydispersity of 1.1-2.6. These PNDIs combined a constant electron affinity of 3.9 eV with an optical band gap that varies from 1.7 eV in PNDISS to 1.4 eV in ePNDIBS due to intramolecular charge transfer. X-ray diffraction analysis of films of the polymers revealed a lamellar crystalline structure in which the lamellar interchain distance varied from 2.45 nm in PNDISS to 2.75 nm in PNDIBDS while the pi -stacking distance varied from 0.397 nm in PNDIBDS to 0.443 nm in PNDISS. Average field-effect electron mobility of 0.008 to 0.24 cm super(2) V super(-1) s super(-1) with high on/off current ratio (10 super(4) to 10 super(6)) was observed from the bottom gate/top contact n-channel OFETs. A 3.4-fold enhancement in electron mobility was observed in phenyl end-capped and high molecular weight ePNDIBS whereas such end-capping had no effect on the electron mobility in PNDISS and PNDIBDS.
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