Light-activated electric bistability for evaporated silver nanoparticles in organic field-effect transistors

Recent advances in organic electric bistability show undeniable potential in applications in the field of information technology due to enviable compatibility with flexible substrates and subsidized fabrication costs. However, such electrical bistability necessitates stable charge storage, which indicates the force equilibrium for the trapped charge and the memory window is formed. Luckily, the assistance of photo-irradiation has been seen as an efficient approach to obtain an organic electric bistability performance. Application of electric field has been proposed to effectively restrain the release of trapped charges, therefore affecting the corresponding memory behavior. Alternatively, desired charge storage can be achieved by embedding metal nanoparticles into the dielectric layer of organic field-effect transistors. However, the trapped charges have been reported to escape soon, after where a potential barrier such as silver nanoparticles has not been used.

Researchers led by Professor Yuguang Ma at the State Key Laboratory of Luminescent Materials and Devices in South China University of Technology employed photo-irradiation to the active electric bistability behavior in organic field-effect transistors embedded with evaporated metal nanoparticles. They designed a novel operation mode to exhibit the memory behavior and to explore the origin of the formation of stable charge states. Their work is now published in the research journal, Phys.Chem.Chem.Phys.

The research team begun their experiment by selecting n-doped silicon and thermally grown silicon (IV) oxide as the back-gate and first gate inorganic gates dielectrics. They then embedded the evaporated naked silver nanoparticles in the isolated layer of PTB7-based organic field-effect transistors where their electric bistability behavior was successfully activated by photo-irradiation.

The authors observed that the devices displayed no obvious memory behavior in the dark; while under weak photo-irradiation, an excellent memory window was achieved. The team noted that the designed varying operation modes exhibited the memory behavior and enabled exploration of the origin of the formation of stable charge state. Furthermore, the researchers noted that surplus photo-generated electric field was generated by the immobilized photo-generated electrons. This was seen to confine the trapped charge in the charge storage media after the gate voltage and photo-irradiation were detached.

The study shows that evaporated silver nanoparticles has been introduced in a PTB7-based organic field-effect transistor, where the electric bistability behavior has successfully been activated by photo-irradiation. The results by Professor Yuguang Ma research team have shown that the photo-irradiation created more charges at the interface, and the presence of silver nanoparticles allowed effective charge storage of the majority carriers, which increased the drain current and lowered the gate-operating voltage. This implicates that the memory window can be achieved at very low light density and does not require strong adsorption.

PTB7 – polymer poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b0]dithiophene-2,6-diyl][3- fluoro- 2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]]  (a classic hole transporting organic photovoltaic polymer)