LED and OLED-based optic sensor array for colourimetric analysis

Abstract

In this report, the development of flexible OLED-based (organic light-emitting diodes) light emitter and detector array is discussed for low-cost colourimetric analysis of water samples. LEDs have been used as optical sensors by measuring their discharge time, when exposed to different light intensities. This report investigates whether an LED emitter and detector array, with different colour LEDs and therefore wavelengths, can be used for colourimetric analysis (specifically a colourimetric pH test). This report also investigates whether flexible OLEDs can be used to create a similar light emission and detection array as the LED array. The flexibility and inkjet printability of OLEDs make it desirable for lab-on-chip, microfluidic, rapid diagnostic devices, which is agrowing field of research. Using OLEDs as light detectors is a novel concept; therefore OLED panels were characterized as light detecting devices in this report in terms of wavelength sensitivities, angular response, emission spectra, discharge time, photocurrent, capacitance, and resistance. These results were compared to the results of an LED, used as a light detector. A discrete model of the OLED was also simulated in SPICE software. The manufacturing of OLEDs was also investigated. Printed electronics is a growing additive manufacturing technique that is capable of printing small, low-cost, printed electronic devices on flexible substrates. Inkjet printed electronics is of special interest as there is little material wastage and high resolutions are attainable. Flexible OLEDs have been manufactured using a combination of screen printing, inkjet printing, and nano-printing techniques. In this report, an investigation was done on whether a fully inkjet printed OLED can be manufactured. A fully inkjet printable OLED structure was simulated, and the layers of the OLED structure and layer thicknesses were then optimized to maximize the number of photons that exit the device.