Near-ultraviolet photodetector based on hybrid polymer/zinc oxide nanorods by low-temperature solution processes

Abstract

In this article, we have proposed a nanostructured near-ultraviolet photodetector ͑Ͻ400 nm͒ based on the ZnO nanorod/polyfluorene hybrid by solution processes at low temperature. The current-voltage characteristic of the hybrid device demonstrates the typical pn-heterojunction diode behavior, consisting of p-type polymer and n-type ZnO nanorods, respectively. The relative quantum efficiencies of the hybrid device exhibit a nearly three order difference while illuminated under UV and visible light, respectively. The responsivity for the device can reach to 0.18 A / W at 300 nm by applying a bias of −2 V, which provides a route to fabricate a low-cost near-UV photodetector.

Fabrication and characterisation of hybrid photodiodes based on PCPDTBT–ZnO active layers

“…To obtain photodiodes with high rectification ratios, efficient charge injection through the PCPDTBT and ZnO layers under forward bias is needed. This was achieved by ensuring that the potential barriers between each layer was low, so the data supports the view that using an MoO3 hole transport layer and Ag electrode minimises this barrier, as ITO-ZnO is already known to form an Ohmic contact [11]. The quality of the polymer film can also influence the diode properties and previous reports from this group show that the mobility of this polymer is high when using hole only devices, when compared to materials such as P3HT [18].…”

“…The solar cell performance under AM1.5G illumination is low, with a Power Conversion Efficiency (PCE) of 0.070%. This is to be expected owing to the planar interface, which usually leads to lower performances than devices based on ZnO nanocrystals or vertically aligned ZnO nanowires, because of the smaller interfacial area between the polymer and acceptor [11]. However, this does compare closely with the 'record' efficiency for a planar HPD.…”

“…ZnO has also been used widely for the development of hybrid photovoltaics or photodiodes (HPDs). In photovoltaics, performances up to 0.11% have been reported for 'planar' devices, where the ZnO is deposited as a flat, uniform surface and up to 0.76% for devices made with ZnO nanowires, which create an interdigitated interface with the organic layer [11]. In addition, up to 2.0% has been reported for devices using ZnO nano-particles/crystals in a bulk-heterojunction configuration with an donor material such as Poly(3-hexylthiophene-2,5-diyl) (P3HT) [11].…”

“…In photovoltaics, performances up to 0.11% have been reported for 'planar' devices, where the ZnO is deposited as a flat, uniform surface and up to 0.76% for devices made with ZnO nanowires, which create an interdigitated interface with the organic layer [11]. In addition, up to 2.0% has been reported for devices using ZnO nano-particles/crystals in a bulk-heterojunction configuration with an donor material such as Poly(3-hexylthiophene-2,5-diyl) (P3HT) [11]. Most work on hybrid devices has focused on photovoltaics and utilised organic semiconductors such as polyfluorene [12], P3HT [11] or polyaniline [13].…”

“…In addition, up to 2.0% has been reported for devices using ZnO nano-particles/crystals in a bulk-heterojunction configuration with an donor material such as Poly(3-hexylthiophene-2,5-diyl) (P3HT) [11]. Most work on hybrid devices has focused on photovoltaics and utilised organic semiconductors such as polyfluorene [12], P3HT [11] or polyaniline [13]. Whilst the performance as photovoltaics is low, the potential as photo-diodes or detectors has not been fully investigated.…”