Role of interchain coupling in the metallic state of conducting polymers.

We investigated the charge dynamics of the conductivity enhancement from 2 to 1000 S/cm in poly(3, 4-ethylenedioxythiophene):poly(styrenesulfonate) as induced by structural changes through the addition of a polar solvent and the following solvent bath treatment. Our results indicate that the addition of a polar solvent selectively enhanced the π-π coupling of the polymer chains, resulting in the reduction of disorder and tremendously increasing the charge carrier mobility, which yielded an insulator-to-metal transition. In contrast, the following solvent bath treatment selectively enhanced the intergrain coupling, which did not affect the disorder or the mobility but increased the charge carrier density. Therefore, we demonstrate that the conduction-character defining disorder in this conducting polymer system is determined by the extent of interchain coupling.

Efficient TCO-free organic solar cells with modified poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) anodes.

Organic photovoltaic cells (OPVs) with a highly conductive poly 3,4-ethylenedioxythiophene:poly styrenesulfonate (PEDOT:PSS) layer as an anode and that were modified with the addition of some organic solvents such as sorbitol (So), dimethyl sulfoxide (DMSO), N-methyl-pyrrolidone (NMP), dimethylformamide (DMF), and ethylene glycol (EG) were fabricated without the use of transparent conducting oxide (TCO). The conductivity of the PEDOT:PSS film that was modified with each additive was enhanced by three orders of magnitude. According to the atomic force microscopy (AFM) study, the conductivity enhancement might have been related to the better connections between the conducting PEDOT chains. The TCO-free solar cells with a modified PEDOT:PSS layer and an active layer composed of poly (3-hexylthiophene) (P3HT) and phenyl [6, 6] C61 butyric acid methyl ester (PCBM) performed as well as the indium-tin-oxide (ITO)-based organic solar cells. The power conversion efficiency (PCE) of the organic solar cells with a DMSO-, So + DMSO-, and EG-modified PEDOT:PSS layer reached 3.51, 3.64, and 3.77%, respectively, under an illumination of AM 1.5 (100 mW/cm2).

Synthesis and characterization of new dithienosilole-based copolymers for polymer solar cells.

A series of dithienosilole-based copolymers, poly [(4,4'-bis(2-hexyl)dithieno[3,2-b:2',3'-d]silole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-5,5'-diyl] (P1), poly[(4,4'-bis(2-hexyl)dithieno[3,2-b:2',3'-d]silole)-2,6-diyl-alt-(2,2'-bithiazole)-5,5'-diyl] (P2), poly[(4,4'-bis(2-hexyl)dithieno[3,2-b:2',3'-d]silole)-2, 6-diyl-alt-(10 -methyl-phenothiazine)-3,7-diyl](P3), poly[(4,4'-bis(2-hexyl)dithieno[3,2-b:2',3'-d]silole)-2,6-diyl-alt-(4,7-bis(2-thienyl)-9,10-anthracene)-5,5'-diyl] (P4) were synthesized by the Pd-catalyzed Stille polymerization method. Electron-deficient benzothiadiazole and bithiazole units and electron-rich phenothiazine and anthracene moieties were incorporated into the polymer backbone to obtain the broad absorption spectrum and to improve the hole-transporting characteristics, respectively. The polymer solar cell (PSC) was fabricated with a layered structure of ITO/PEDOT:PSS/polymer:C71-PCBM (1:3)/LiF/Al. The best performance of PSC was obtained at P3:C71-PCBM which reaches a power conversion efficiency (PCE) of 1.18%, with a short circuit current density (J(sc)) of 4.75 mA/cm2, an open circuit voltage (V(oc)) of 0.71 V, and a fill factor (FF) of 0.35 under AM 1.5G irradiation (100 mW/cm2).

A series connection architecture for large-area organic photovoltaic modules with a 7.5% module efficiency.

The fabrication of organic photovoltaic modules via printing techniques has been the greatest challenge for their commercial manufacture. Current module architecture, which is based on a monolithic geometry consisting of serially interconnecting stripe-patterned subcells with finite widths, requires highly sophisticated patterning processes that significantly increase the complexity of printing production lines and cause serious reductions in module efficiency due to so-called aperture loss in series connection regions. Herein we demonstrate an innovative module structure that can simultaneously reduce both patterning processes and aperture loss. By using a charge recombination feature that occurs at contacts between electron- and hole-transport layers, we devise a series connection method that facilitates module fabrication without patterning the charge transport layers. With the successive deposition of component layers using slot-die and doctor-blade printing techniques, we achieve a high module efficiency reaching 7.5% with area of 4.15 cm(2).

Simplified tandem polymer solar cells with an ideal self-organized recombination layer.

A new tandem architecture for printable photovoltaics using a versatile organic nanocomposite containing photoactive and interfacial materials is demonstrated. The nanocomposite forms an ideal self-organized recombination layer via a spontaneous vertical phase separation, which yields a simplified tandem structure fabricated with only four component layers and a high tandem efficiency of 10.8%.

Effects of hole and electron transporting interlayers for inverted polymer solar cells.

An efficient inverted polymer solar cell (PSC) with a transparent amorphous titanium oxide (TiOx) as an electron transporting layer (ETL) between bottom electrode and photo-active layer, and a tungsten oxide (WO3) inserted as a hole transporting layer (HTL) was fabricated. Introducing of ETL and HTL results in increases in the open circuit voltage (VOC), short circuit current (JSC) and the fill factor (FF). The inverted PSC device with TiOx and WO3 layer showed the higher power conversion efficiency (PCE) than that of conventional PSC. The PCE of 3.73% was achieved at inverted device, and was retained over 87% of its initial efficiency after 25 days in the ambient air without encapsulation.

Fano resonance in crossed carbon nanotubes.

We report the observation of the resonant transport in multiwall carbon nanotubes in a crossed geometry. The resonant transport is manifested by an asymmetric peak in the differential conductance curve. The observed asymmetric conductance peak is well explained by the Fano resonance originating from the scattering at the contact region of the two nanotubes. The conductance peak depends sensitively on the external magnetic field and exhibits Aharonov-Bohm-type oscillation.