High-Bandwidth Organic Light Emitting Diodes for Ultra-Low Cost Visible Light Communication Links

Visible light communications (VLC) have attracted considerable interest in recent years due to an increasing need for data communication links in home and enterprise environments. Organic light-emitting diodes (OLEDs) are widely used in display applications owing to their high brightness, high quality colour-rending capability and low cost. As a result, they are attractive candidates for the implementation of ultra-low cost visible light optical links in free-space and guided-wave communications. However, OLEDs need to exhibit a bandwidth of at least ~MHz to be able to support the modest data rates (~Mbps) required in these applications. Although fluorescent OLEDs typically exhibit shorter photon lifetimes than inorganic LEDs, the bandwidth performance of the large size OLEDs used in display applications are limited by their electrical characteristics. In this work, we present a detailed physical simulation that describes well the performance of fast OLED devices that exhibit significant -3 dB bandwidths (f3dB) of 44 MHz obtained for a 0.12 mm² device. It is demonstrated that the reduction of the device size results in a significant bandwidth improvement due primarily to a reduction in parasitic capacitance of the devices, though this is counteracted by carrier dynamic effects. The model provides an insight into the basic physical properties of the OLED and may be used for optimisation of future generations of OLED devices.

1. INTRODUCTION

In an era of ever-increasing data generation and transmission, visible light communications (VLC) has attracted significant interest for end-user applications. Organic LEDs (OLEDs) can be deposited using a variety of technologies on a multitude of different substrates. They show high brightness and have a relatively low cost, making them good candidates for low-cost VLC links [1], particularly as advanced coding and array techniques may eventually enable >Gbps aggregate data rates [2]. However, the inherently low mobility of organic semiconductors means that they are often bandwidth-limited and can struggle to achieve the ~Mbps data rates required (at a minimum) for use in communications. Nonetheless, with analysis and optimisation afforded by simulation and modelling techniques, it may be possible to understand better the behaviour of such organic devices and correspondingly to optimise their design for such high-bandwidth applications.