High Aspect Ratio and Post-Processing Free Silver Nanowires as Top Electrodes for Inverted-Structured Photodiodes

Abstract

Silver nanowires (Ag NWs) as transparent conducting electrodes are widely used in many applications such as organic light-emitting diodes (OLEDs), polymer light-emitting diodes, touch screens, solar cells, and transparent heaters. In this work, using a large-scale synthesis, the synthesized Ag NWs had a high aspect ratio of 2820. The Ag NWs could be applied as a top transparent electrode in a device by simple drop-casting without any post-processing steps. The fabricated device comprised 4,4'-bis(carbazol-9-yl)biphenyl/MoO₃ organic/inorganic layers which are parts of the inverted structure OLEDs or solar cells. The photodiode characteristics at the UV range were observed in the device. The ability of Ag NWs to replace opaque metals as top electrodes in a device has been demonstrated.

Figure 1

(a) SEM image, (b) TEM image of Ag NWs obtained in large scale synthesis, (c) photo of the dispersion of Ag NWs in IPA, (d) XRD pattern of Ag NWs with the reference pattern of Ag (JCPDS no. 004-0783), and (e) UV–vis spectrum of synthesized Ag NWs.

Figure 2

UV–vis transmission spectra of the Ag NW electrode and of the ITO one. The black arrow shows the transmissions of the Ag NW electrode and ITO electrode at a wavelength of 340 nm.

Figure 3

(a) Device structure, (b) flat band diagram of the CBP/MoO₃ photodiode using Ag NWs as the top electrode with the flow directions of photogenerated electrons and holes across the device, (c) photo of the real device under UV light illumination with the inset showing the device on a paper under room light, and (d) SEM image of Ag NWs as the top electrode in the device. The work functions for ITO, CBP, MoO₃, and Ag NWs in the device are obtained based on references.^,

Figure 4

(a) Responsivity versus wavelength, (b) I–V curve, (c) photocurrent vs optical power, and (d) on/off switching curves (under zero-bias conditions) of CBP/MoO₃ photodiodes using Ag NWs as the top electrode and ITO as the bottom electrode.

Figure 5

Synthesis procedure of Ag NWs.