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Charge transport properties in thin films of Poly(2‐methoxy‐5‐(3′,7′‐dimethyloctyloxy)‐1,4‐phenylenevinylene) (MDMO PPV) cast using either chloroform (CF), toluene (TOL), or chlorobenzene (CB) as solvent were investigated. Hole mobility (μ) in these thin films measured using time‐of‐flight transient photoconductivity showed an increasing trend with respect to the solvent used in the same order, that is, μCF (2.4 × 10−7 cm2/Vs) < μTOL (6.9 × 10−7 cm2/Vs) < μCB (2.3 × 10−6 cm2/Vs). Observed variations in mobilities were attributed to different morphologies of MDMO PPV chains in thin films cast using the aforesaid solvents. Nature of the interchain interactions and aggregate formation were obtained using photoluminescence (PL), Raman spectroscopy, and AFM studies. Ratio of PL peak intensities of 0–0 and 0–1 transitions, which is a direct measure of interchain interaction, was the highest in CB and lowest in CF. Variation in the relative intensities of out‐of‐plane wagging of vinylene group (∼963 cm−1 mode) in Raman spectra suggested different extent of coiling of polymer chains in these thin films. From these observations, it was elicited that aggregate size and interchain interactions are highest in CB and least in CF. AFM‐based topographic images of thin films further supported these variations in the size of aggregates. Variation in the aggregate sizes and interchain interactions explained the corresponding variation in the mobility. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1431–1439

The effect of oligomer concentration on the performance of polymer and oligomer blended system based photo-detectors was investigated. Improvement in dark rectification ratio and photoresponse of diode were observed in the blended system photodetectors compared to pristine polymer based photodetectors. The photodetectors fabricated with poly(3hexylthiophene) (P3HT) and α, ω-di-hexyl-sexithiophene (DH6T) were tuned to two different wavelengths namely 525 nm and 400 nm respectively, corresponding to the maximum of the absorption of polymer and oligomer materials respectively. It was observed that the effective conjugation length and disorder in the polymer chains critically affect the photoresponse of organic optoelectronic devices. In this study, improvement in effective conjugation length and disorder were observed as the concentration of DH6T in the blend was increased; leading to the enhancement in the photoresponse of the fabricated device with these blends. Herein, with the increase of DH6Tconcentartion in the blended thin films, the photoresponsivity of fabricated photodetectors towards near UV at ∼400 nm wavelength in addition to the 525 nm wavelength was found to be increased. Comparable photosensitivity (∼1.6×10 3 ) and responsivity (∼18 A W −1 ) were achieved for both the wavelengths separately, in the blended photodetectors fabricated with a DH6T concentration of 40%. Such devices tuned to dual wavelength may also find their application in the field of optically switched logic gates.

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