Organic phototransistor from solution cast, ordered crystals assembly of a pentacene derivative

Abstract

Fabrication of organic crystals assembly of a small molecule, viz, 6,13 bis(tri-isopropylsilylethynyl) pentacene by solution casting is reported. The pentacene derivative is chosen because of its excellent crystal forming ability and reasonably high solubility in a range of organic solvents. Solution-processed crystals of 6,13 bis(tri-isopropylsilylethynyl) pentacene are deposited from high boiling point solvent and show strong molecular ordering. Based on the solution-processed crystals, bottom-contact organic field-effect transistors and organic phototransistors have been fabricated, producing excellent device performances. Transistors based on the said molecule exhibit high on/off current ratio (>103) and a maximum field-effect mobility ~0.49 cm2 V−1 s−1. Moreover, phototransistor fabricated from said crystals exhibits fast response speed, good photoresponsivity (ca. 0.4 A W−1), high photo to dark current ratio (ca. 500) and reproducible and reversible photoswitching characteristics under visible illumination. Dependence of photocurrent on illumination intensity indicates an effective way for controlling photo-carriers generation in active material and hence of tuning and modulating device’s performance. The ability to make large area organic crystals through solution processing opens up new possibilities for integrated device applications of organic nanostructures for future large-scale and low-cost plastic optoelectronic devices.