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Varied-length conjugated polyelectrolytes (2–5 methylene units) containing CPDT-alt-BT were synthesized to study the optical, electrochemical, and morphological properties. These were used in accumulation mode organic electrochemical transistors.

Polymers using thieno[2,3-b]indole (2-TI) with high planarity were synthesized and utilized for the photovoltaics. Conjugated polymers (PTIDTBT, PTIFDTBT and PTIDFDTBT) containing 2-TI as electron-donating unit and fluorinated DTBT as electron-accepting unit were synthesized. To enhance the effect of lowering highest occupied molecular orbital (HOMO) energy level for the high open-circuit voltages (VOC), we utilized new thieno[2,3-b]indole (2-TI) moiety as the weak electron-donating group and the fluoro-substituted electron-accepting BT unit. The polymer composed of BT with two fluorine unit coupled with 2-TI, PTIDFDTBT, shows higher VOC out of the series. The device comprising PTIDFDTBT and PC71BM (1:3) showed a VOC of 0.79 V, a JSC of 8.39 mA/cm2, and a fill factor (FF) of 0.48, giving a power conversion efficiency of 3.21%.

For the utilization in the polymer solar cells, conjugated polymers were synthesized using electron-deficient units, 2-{3-[4,6-bis-(4-hexyl-thiophen-2-yl)-pyrimidin-2-yl]-phenyl}-thiazolo[5,4-b]pyridine (mTP) or 2-{4-[4,6-bis-(4-hexylthiophen-2-yl)-pyrimidin-2-yl]-phenyl}-thiazolo[5,4-b]pyridine (pTP). To increase the electron-deficiency of the pyrimidine unit, thiazolopyridine (TP), strong electron-withdrawing group, was incorporated at the meta-/para-position of the phenylene connector which is attached to the pyrimidine. It was confirmed that the TP unit at para-position has stronger intramolecular charge transfer (ICT) effect to shift the absorption to the longer wavelength region and deepens the highest occupied molecular orbital (HOMO) energy level. The polymers with 4-(1-octylnonyl)-6-(2-thienyl)-4H-thieno[3,2,-b]indole (TTI) having the decent solubility for the morphology show the superior open-circuit voltage (V OC ) value of the mTTI/pTTI devices compared to the others. Also, the polymers with TTI show increased short-circuit current (J SC ), fill factor (FF), and power conversion efficiency (PCE) due to high face-on populations.

The development of new techniques that can be used to modify the molecular orientations and structures of organic compounds in organic thin films is in urgent demand to overcome the low levels of charge transport in such films and to ultimately achieve high-efficiency organic opto-electronics. Here, we report structural transformation and electrical characterization of a poly(3-hexylthiophene) (P3HT) semiconductor thin film under femtosecond laser irradiation at a level below the ablation threshold. A combination of grazing incidence X-ray diffraction and near edge X-ray absorption fine structure analyses reveal that the laser procedure effectively switches the P3HT orientation from edge-on to face-on, and the stability of this face-on orientation was also confirmed. Various laser fluence levels ranging up to the ablation threshold were tested, and the P3HT film with a transformed face-on orientation resulting from the optimized fluence level showed a charge current in the vertical direction three times greater than did the pristine film. This enhancement in the charge current was attributed to the vertical π–π stacking of the face-on orientation. These results also confirmed the effectiveness of our novel method for modifying organic thin films, and we expect this method to be attractive for the development of organic electronics and hybrid device applications.

In this report, a series of copolymers based on 6-(2-thienyl)-4H-thieno[3,2-b]indole (TTI) as an electron-rich unit and fluorinated DTBT as an electron-deficient unit were synthesized, namely PTTIF1 and PTTIF2, and applied to photovoltaic devices. TTI unit was coupled with fluorinated DTBT to utilize the merit of introduction of fluorine atom leading to the lowering of the HOMO energy level while keeping high planarity of the conjugated backbone. The synthesized copolymers show a noticeable change in HOMO energy levels as compared with non-fluorinated polymer (PTTIDTBT-h). Optimized photovoltaic devices of PTTIF2 exhibited power conversion efficiency of 4.36% with decent JSC and FF values, which can be explained by the higher charge transporting ability of PTTIF2 with preferable face-on crystallite population than PTTIF1 in grazing incident wide-angle X-ray scattering (GIWAXS).