UV‐Sensing Semitransparent Organic Field‐Effect Transistors with Wide Bandgap Small Molecular Channel and Polymeric Gate‐Insulating Layers

Abstract

This study demonstrates UV‐sensing semitransparent organic field‐effect transistors (OFETs) with wide bandgap small molecular channel and polymeric gate‐insulating layers. N,N′‐di(1‐naphthyl)‐N,N′‐diphenyl‐(1,1′‐biphenyl)‐4,4′‐diamine (NPB) is employed as the wide bandgap channel layer, while poly(methyl methacrylate) is introduced as the wide bandgap gate‐insulating layer. The performance of OFETs is optimized by NPB thickness control and thermal treatment. Results show that the best device performance (on/off ratio = 4.7 × 106 and hole mobility = 4.2 × 10−5 cm2 V−1 s−1) is achieved by thermal treatment of the 130 nm thick NPB layers at 70 °C for 30 min leading to a noticeably changed surface morphology in the NPB layers. The optimized OFETs exhibit excellent operation stability without hysteresis, while those with semitransparent silver electrodes deliver quite a good transparency. The semitransparent OFETs can sensitively detect a UV light with high stability even though no photoresponse is measured under a visible light.

Light‐Insensitive Organic Field‐Effect Transistors with n‐Type Conjugated Polymers Containing Dinitrothiophene Units

“…The similar trend with the film thickness was measured for the transfer curves in Figure b. This result indicates that 75 nm is an optimum thickness for maximizing the channel current by the trade‐off between charge transport volume (capacity) and effective field‐effect zone (distance) because the thicker channel layers can deliver higher charge transport capacity but the effective field effect cannot reach the channel region far from the gate electrodes . Here, it is noted that all devices exhibited very low off current (<10 pA) irrespective of the PODTPPD‐DNT thickness.…”

“…Considering that the thickness of channel layers in OFETs is usually in the range of ≈50 nm or less, a reasonable transparency can be made if electrodes are transparent (metal oxides) or semitransparent (metals) . However, there should be large fluctuations in drain current when the OFETs with the (semi)transparent electrodes are operated under daylight (or room light) condition because most organic semiconducting materials can absorb ultraviolet (UV) and/or visible (vis) light including near‐infrared (NIR) light in some cases .…”

Recent Progress in Organic Phototransistors: Semiconductor Materials, Device Structures and Optoelectronic Applications

“…Furthermore, they are easily integrated in electronic circuitry for their complementary metal‐oxide‐semiconductor (CMOS)‐like configuration . The physical processes of OPTs involve the absorption of light in particular wavelength, the exciton formation, exciton diffusion, exciton dissociation and the transport of resulting free charge carriers. Each step has a significant impact on the device performance.…”

“…Upon light irradiation, the excitons which have a relatively high binding energy, are generated in the organic semiconductor materials . The high exciton binding energy is ascribed to a combination of weak electron‐electron correlation and low dielectric constant in organic materials, and not favorable for the exciton dissociation, compared to the ones in inorganic semiconductors.…”

Effect of Top Channel Thickness in Near Infrared Organic Phototransistors with Conjugated Polymer Gate-Sensing Layers

“…On this account, organic photodetectors with organic sensing layers have been recently spotlighted because organic materials can bestow better softness and flexibility than inorganic materials [15][16][17]. In particular, organic phototransistors (OPTRs), which are based on organic field-effect transistors (OFETs), have attracted keen interest due to their capability of signal amplification by three-electrode structures, leading to maximizing sensitivity [18][19][20][21][22][23]. Organic channel layers in most organic phototransistors act as a sensing medium at the same time and typically are placed beneath source/drain electrodes, even though some top channel layers (above source/drain electrodes) have been attempted for the purpose of visible light detection [19,[24][25][26].…”