Nanoimprinted transparent metal electrodes and their applications in organic optoelectronic devices

A new type of transparent and conductive electrode (TCE) in the form of nanoscale periodically perforated metal mesh film by nanoimprint lithography (NIL) has been developed. The developed transparent metal electrodes have the characteristics of high optical transmittance and electrical conductivity, a combination of properties that makes them suitable as a replacement for indium-doped tin oxide (ITO), a predominant choice as a TCE for organic optoelectronic device applications. Not only do metals provide different work functions, but also nanoscale metallic gratings exhibit unique optical properties due to the excitation of surface plasmon resonance (SPR), which can be exploited in specially designed solar cells to achieve enhanced light absorption. The future low-cost and high performance organic optoelectronic devices will need a TCE which should be available with low-cost and high mechanical stability, the properties which ITO does not have. This work shows that transparent metal (e.g. Cu) electrodes on flexible plastic substrates exhibit not only high transmittance and conductivity, but also a superior mechanical strength to compared ITO electrode.;Organic light emitting diodes (OLEDs) and Organic solar cells (OSCs) have been demonstrated using transparent metal (Au, Ag, and Cu) electrodes as a TCE on both hard (glass) and soft (PET) substrates and showed comparable performance to the device using conventional ITO electrode. To demonstrate the possibility of PCE enhancement of OSCs using developed metal electrode, OSCs have been fabricated with a periodic (220 nm) Ag grating electrode, acting as not only a transparent electrode but also to support surface plasmon modes with localized and concentrated light distribution. Absolute PCE enhancement of about 35% for the device with Ag electrode relative to the ITO device was achieved. It has also been demonstrated that the SPR enhances the external quantum efficiency (EQE) by about 2.5 times for the Ag device compared to the ITO device. The experimental results suggested that higher enhancement would be possible for a thinner organic layer. Therefore, the use of transparent metal electrode as a TCE instead of ITO could help to realize low-cost, high performance large area flexible organic optoelectronic devices such as OSCs and OLEDs.