Boosting the Performance of Organic Phototransistors Utilizing Oriented Thin-Films of Liquid Crystalline Conjugated Polymer PBTTT C-14

Abstract

To improve the organic field-effect transistor (OFET) performance, the advantages of the unidirectional floating film transfer method (UFTM) are utilized to fabricate uniaxially aligned thin film of a liquid crystalline semiconducting polymer (SCP) upon a SiO2 surface modified with a self-assembled monolayer (SAM) of alkyl-silane. We deposited the SAM of octadecyl-triethoxy silane (OTES) by spin coating onto the SiO2 gate dielectric surface to make the surface hydrophobic and promote the molecular self-assembly of aligned SCP. The electrical anisotropy of the UFTM fabricated thin films of poly [2,5-bis (3-tetradecylthiophen-2-yl) thieno [3,2-b] thiophene] (PBTTT) C-14 were studied by constructing parallel and perpendicular OFETs. Parallel OFET exhibits a mobility of 0.13 cm2 V−1sec−1, a dark on-off ratio of 2.6 × 105, and 0V Vth. Further, OFETs are utilized as organic phototransistors (OPTs) under monochromatic green light (525 nm) illumination at an intensity of 3 mWcm−2. The photosensitivity and responsivity of parallel OPT are 6.3 × 104 and 81 AW−1, respectively, which are much more pronounced compared to that of the corresponding perpendicular OPT with the photosensitivity and responsivity of 2 × 102 and 6.2 AW−1, respectively. This work contributes to the advancement of organic photodetector technology, offering valuable guidance for future device development and applications. © 2025 Wiley-VCH GmbH.