The University of Hong Kong, Hong Kong
Title: Distinct multi-physical effects of plasmonic metal nanostructures for high performance optoelectronic devices
Biography: W C H Choy
The remarkable enhancement of plasmon -optical and -electrical effects by metal nanostructures will be described in detail for high performance optoelectronic devices such as light emitting diodes and solar cells. Taking plasmonic organic solar cell as an example, the power conversion efficiency can reach over 10.5%. The plasmon-optical effects have been utilized to optically enhance active layer absorption in organic solar cells (OSCs). The exploited plasmonic resonances of metal nanomaterials are typically from the fundamental dipole/high-order modes with narrow spectral widths for regional OSC absorption improvement. The conventional broadband absorption enhancement (using plasmonic effects) needs linear-superposition of plasmonic resonances. Moreover, with appropriate incorporation of metal nanostructures into the multilayered OSCs, plasmon-electrical effects can be introduced to improve the electrical properties of carrier transport layer and eliminate the space charge limit of organic active layer. In this talk, we will describe the details of the plasmon -optical and -electrical effects by introducing metal nanostructures on different layer of OSCs. Recently, through strategic incorporation of gold nanostars (Au NSs) in between hole transport layer (HTL) and active layer, the excited plasmonic asymmetric modes offer a new approach toward broadband enhancement. Remarkably, the improvement can be explained by energy transfer of plasmonic asymmetric modes of Au NS. Moreover, Au NSs simultaneously deliver plasmon-electrical effects which shorten transport path length of the typically low-mobility holes and lengthen that of high-mobility electrons for better balanced carrier collection. Meanwhile, the resistance of HTL is reduced by Au NSs. Consequently, PCE of 10.5% has been achieved through cooperatively plasmon-optical and -electrical effects of Au NSs. With the understanding of the multi-physical (optical and electrical) effects, we will also demonstrate significant performance improvement of plasmonic nanostructures for organic light emitting diode applications.