A Study on Charge Selective Transport for Highly Efficient Polymer Based Optoelectronic Devices

Abstract

Polymer based optoelectronic devices including polymer light-emitting diodes (PLEDs) and polymer solar cells (PSCs) have been recently focused for display, energy source and flexible electronic applications because of their advantages such as low cost, light weight, easy solution process fabrication and mechanical flexibility. Moreover, so much effort has been made to maximize their device performance through optimization of device configuration and charge selective transport. In particular, balanced charge transport via charge selective interfacial engineering or surface modification is promising for optimized device performance. According to the device configuration, interfacial engineering can improve the minority carrier transport with well-matched energy level, passivate the charge trap sites and enhance the materials compatibility. It can also block abundant majority carrier and reduce the exciton quenching, leading to improving the recombination rate of balanced charges in PLEDs while disrupting bimolecular recombination in PSCs. Here, I present variety interfacial engineering strategies employing modified charge transport layer such as graphene oxide (GO) as a hole transport layer (HTL) in conventional PLEDs and surface modified zinc oxide (ZnO) as an electron transport layer (ETL) using ionic liquid molecules (ILMs), conjugated polyelectrolyte (CPE) and amine-based polar solvents in inverted polymer light-emitting diodes (iPLEDs) and polymer solar cells (iPSCs). A GO layer with a wide band gap blocks transport of electrons from an emissive layer to an indium tin oxide (ITO) anode while reduces the exciton quenching between the GO layer and the emissive layer. As a result, the GO layer maximizes hole-electron recombination within the emissive layer leading to improvement of device performance in PLEDs. In addition, surface modified ZnO layers with various interfacial layers such as ILMs, CPE and amine-based polar solvents remarkably enhance the devices performance by introducing spontaneously oriented interfacial dipoles between the ZnO layer and active layer in iPLEDs and iPSCs. This charge selective interfacial engineering is a promising way for organic optoelectronic devices such as organic photovoltaics (OPVs), organic light-emitting diodes (OLEDs), organic thin film transistors (OTFTs), and organic laser diodes (OLDs).