Optically switchable transistor via energy-level phototuning in a bicomponent organic semiconductor

Abstract

Organic semiconductors are suitable candidates for printable, flexible and large-area electronics. Alongside attaining an improved device performance, to confer a multifunctional nature to the employed materials is key for organic-based logic applications. Here we report on the engineering of an electronic structure in a semiconducting film by blending two molecular components, a photochromic diarylethene derivative and a poly(3-hexylthiophene) (P3HT) matrix, to attain phototunable and bistable energy levels for the P3HT's hole transport. As a proof-of-concept we exploited this blend as a semiconducting material in organic thin-film transistors. The device illumination at defined wavelengths enabled reversible tuning of the diarylethene's electronic states in the blend, which resulted in modulation of the output current. The device photoresponse was found to be in the microsecond range, and thus on a technologically relevant timescale. This modular blending approach allows for the convenient incorporation of various molecular components, which opens up perspectives on multifunctional devices and logic circuits.

Electronic Properties of Optically Switchable Photochromic Diarylethene Molecules at the Interface with Organic Semiconductors

“…13) dissolved in chloroform solvent were directly spin coated onto Au substrates. The thickness of the films was varied by adjusting spinning speed and solution concentration.…”

“…Using PCOMs in blends with organic semiconductors or as photo-addressable interlayer between an organic semiconductor and an electrode, the photo-induced switching can tune charge transport as well as charge injection (extraction) properties in photoswitchable devices. [13][14][15][16] The underlying reason is that the energy level offset between the highest occupied molecular orbital (HOMO) level of PCOMs and either the Fermi level (E F ) of the electrodes and/or the valence band of the organic semiconductor in the device are minimized for one isomer state and maximized for the other, as selected by appropriate photo-induced switching. Analogous arguments apply when considering the lowest unoccupied molecular orbital (LUMO) level and the conduction band.…”

“…[10] It was reported that this change in IE can be used to alter the current through the channel of organic field effect transistors (OFET) where DAE molecules were blended into the polymeric semiconductor poly(hexylthiophene) (P3HT). [12,13] Nevertheless, the energy level alignment (ELA) at the electrode/DAE as well as the organic semiconductor/DAE interfaces is not comprehensively understood. Particularly with respect to metal electrodes, the energy position of DAE frontier levels is yet unknown, and even the ability to photo-switch the molecules in proximity to the metal can questioned due to dipole selection rules.…”

“…Consequently, the electrical properties of the devices are modulated by either the formation of photoswitchable trap states or energy barriers for charges at organic/PCOM or metal/PCOM interfaces, and multifunctionality is realized as the device can be addressed electrically and optically. [13,15] The application of PCOMs in electronic devices requires high thermal stability of the material in its individual isomer state, and at the same time, a highly efficient and robust photoisomerization process. Therefore, DAE molecules show promising potential due to their high fatigue resistance and thermal bistability.…”

Electrochemical Switching of Conductance with Diarylethene-Based Redox-Active Polymers

“…4−6 Light-switching within self-assembled monolayers (SAMs), 7−9 and in polymer films 10−12 has been demonstrated by several groups to date, 13,14 with azobenzene, 15 spiropyran, 16 and diarylethene 17 photochromic switches playing an important role as the photoresponsive elements in such systems. 18−20 A major challenge associated with the use of SAMs and thin (e.g., < 20 nm) polymer films in organic electronic devices, however, is that the magnitude of the change in conductance achievable is limited by the background tunneling current, which limits applications in organic-based devices.…”