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We report a new type of ordered monolayer for the surface modification of organic semiconductors. Fullerene derivatives with fluorocarbon chains ([6,6]-phenyl-C(61)-buryric acid 1H,1H-perfluoro-1-alkyl ester or FC(n)) spontaneously segregated as a monolayer on the surface of a [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) film during a spin-coating process from the mixture solutions, as confirmed by X-ray photoelectron spectroscopy (XPS). Ultraviolet photoelectron spectroscopy (UPS) showed the shift of ionization potentials (IPs) depending on the fluorocarbon chain length, indicating the formation of surface dipole moments. Surface-sensitive vibrational spectroscopy, sum frequency generation (SFG) revealed the ordered molecular orientations of the C(60) moiety in the surface FC(n) layers. The intensity of the SFG signals from FC(n) on the surface showed a clear odd-even effect when the length of the fluorocarbon chain was changed. This new concept of the surface-segregated monolayer provides a facile and versatile approach to modifying the surface of organic semiconductors and is applicable to various organic optoelectronic devices.

Abstract: Precise control of the molecular arrangements at the interface between the electron donor and acceptor in mixed bulk heterojunctions (BHJs) remains challenging, despite the correlation between structural characteristics and efficiency in organic photovoltaics (OPVs). This study reveals that the substitution patterns of linear and branched alkyl side chains on electron‐donating/‐accepting alternating copolymers can control the positions of an acceptor molecule (C60) around the π‐conjugated main chains in mixed BHJs. Two‐dimensional solid‐state NMR demonstrates a marked difference in the location of C60 in the blend films. A copolymer with an electron‐accepting unit positioned in close proximity to C60 demonstrated higher OPV performance in combination with various fullerene derivatives. This molecular design offers precise control over the interfacial molecular structure, thereby paving the way for overcoming the current limitations of OPVs comprising mixed BHJs. [ABSTRACT FROM AUTHOR]

End-functionalized poly(3-butylthiophene) with a thiol group (P3BT-S) was synthesized and used to form a self-assembled monolayer (SAM). It can induce the end-on orientation in the thin film which has the potential to further enhance hole mobility up to 1.1 × 10−2 cm2 V−1 s−1 in the vertical direction. [ABSTRACT FROM AUTHOR]

A fullerene attached all-semiconducting polymer was synthesized and applied to single component polymer photovoltaic cells. The current approach gives a method of obtaining a reliable donor acceptor mixing morphology by molecular design and achieving efficient photovoltaic devices with long thermal stability. [ABSTRACT FROM AUTHOR]

A novel semiconducting polymer poly(4-hexyloxythiazole) with a low optical band gap of 1.4 eV was synthesized and used in organic electronic devices. X-ray diffraction (XRD) measurements reveal a high degree of crystallinity and lamellar packing of poly(4-hexyloxythiazole) in the film similar to poly(3-hexylthiophene). Field effect transistor charge mobility of poly(4-hexyloxythiazole) arrived 0.02 cm 2 /V s. Bulk heterojunction type solar cells based on poly(4-hexyloxythiazole) shows a photoresponse up to about 900 nm. [ABSTRACT FROM AUTHOR]

Controlling the orientation of highly anisotropic structures of polymers is important because the majority of their mechanical, electronic, and optical properties depend on the orientation of the polymer backbone. In thin films, the polymer chains tend to adopt an orientation parallel to the substrate; therefore, forcing the chains to stand perpendicular to the substrate is challenging. We have developed a simple way to achieve this end-on orientation. We functionalized one end of a poly(3-butylthiophene) (P3BT) chain with a 1H,1H,2H,2H,3H,3H-perfluoroundecyl group, which caused spontaneous self-segregation of the polymer (P3BT-F17) to the surface of the polymer film. In P3BT-F17/polystyrene (PS) blend films, a highly ordered end-on orientation of the conjugated backbone was observed in the surface-segregated layer of the crystalline P3BT-F17. Furthermore, when the film was spin-coated from a mixture of P3BT-F17 and P3BT, the chain orientation of P3BT-F17 at the surface forced the P3BT in the bulk of the film to adopt the end-on orientation because of the high crystallinity of P3BT. The electronic conductivity measured perpendicular to the film surface also reflected the end-on orientation in the bulk, resulting in a more than 30-fold enhancement of the hole mobility. [ABSTRACT FROM AUTHOR]