Optically switchable organic field-effect transistors based on photoresponsive gold nanoparticles blended with poly(3-hexylthiophene)

Abstract

Interface tailoring represents a route for integrating complex functions in systems and materials. Although it is ubiquitous in biological systems--e.g., in membranes--synthetic attempts have not yet reached the same level of sophistication. Here, we report on the fabrication of an organic field-effect transistor featuring dual-gate response. Alongside the electric control through the gate electrode, we incorporated photoresponsive nanostructures in the polymeric semiconductor via blending, thereby providing optical switching ability to the device. In particular, we mixed poly(3-hexylthiophene) with gold nanoparticles (AuNP) coated with a chemisorbed azobenzene-based self-assembled monolayer, acting as traps for the charges in the device. The light-induced isomerization between the trans and cis states of the azobenzene molecules coating the AuNP induces a variation of the tunneling barrier, which controls the efficiency of the charge trapping/detrapping process within the semiconducting film. Our approach offers unique solutions to digital commuting between optical and electric signals.

Fig. 1.

Chemical formula of (A) S-[4-[4-(phenylethynyl)phenyl]-ethynyl]benzene-thiol ester (acetyl-OPE) and (B) the azo-biphenyl with an acetyl-protected terminal thiol anchoring group (acetyl-AZO) and its isomerization reaction between the trans and the cis form. Schemes of the differently coated Au nanoparticles: (C) OPE-NP, (D) AZO-NP in its trans and cis form. (E) Scheme of the bottom-contact/bottom-gate field-effect transistor in which S (source), D (drain), and G (gate) are the three terminals and the semiconducting material is a blend of P3HT and the coated Au nanoparticles.

Fig. 2.

Output characteristics of (A) P3HT, (B) OPE-NP/P3HT, (C) a-AZONP/P3HT, and (D) s-AZONP/P3HT recorded at different V_G (-40, -20, 0, 20, and 40 V). Black indicates the initial state (after keeping the device in the dark for 24 h); red, after 45 min of UV irradiation; and grey, after a further 24 h in dark. Channel length (L). 5 μm.

Fig. 3.

Maximum percentage of variation during the irradiation cycles for the (A) V_TH, (B) mobility (μ), and (C) I_D, max (extracted in the linear regime, V_SD = -10 V), for the five different devices. Blue, P3HT; red, s-AZONPs; green, a-AZONPs; magenta, OPE-NPs.

Fig. 4.

Transfer characteristics (V_D = -30 V, L = 5 μm) obtained for the four different devices: black, when the device is in dark; red, when the device is under UV (the measurement started to be recorded after 5 min of irradiation). (A) P3HT, (B) OPE-NPs/P3HT, (C) a-AZONPs/P3HT, and (D) s-AZONPs/P3HT.

Fig. 5.

Photoresponse cycles over time of s-AZONPs/P3HT (in black), OPE-NPs/P3HT (in red), and P3HT (in blue). For the latter, the I_D/I_D, min was multiplied by 100 to allow a better comparison. (A) Four cycles, (B) 10 cycles, and (C) 25 cycles. V_G - V_TH = -4 V, V_D = -10 V, and L = 5 μm.