Photoconduction in Alq3

TL;DR

This study investigates the photoconduction properties of Alq3 thin films, measuring carrier generation efficiency, mobility, and space charge effects to better understand its photoelectronic behavior in device applications.

Contribution

It provides quantitative analysis of photocarrier generation, mobility, and space charge effects in Alq3, offering new insights into its photoconductive mechanisms and material quality indicators.

Findings

Photocarrier quantum efficiency is about 10%.

Quantum efficiency is largely independent of electric field.

Space charge effects cause saturation and phase shift in photocurrent.

Abstract

Photoelectronic properties of Alq3 were studied by photoconductivity measurements in thin film, sandwich (ITO/Alq3/LiF/Al) devices. We find that the photocurrent is dominated by bulk generation of carriers for incident photon energies greater than 2.75 eV. The quantum efficiency of photocarrier generation has been measured from carrier collection measurements to be about 10%. The quantum efficiency is largely independent of electric field. This enables a direct measurement of the electric field dependence of mobility using photoconductivity measurements, which is used for quantitative analysis of the dark forward current in these devices. Photoconductivity measurements were also used to obtain (\mu_{0n} \tau_n) product which can be used as a measure of material quality. For Alq3, we find that the value of (\mu_{0n} \tau_n) product was between 3x10^{-15} cm^2/V to 8x10^{-15} cm^2/V for different samples. In forward bias, at high field the photocurrent shows saturation accompanied by a phase shift. These effects are attributed to space charge effects in the device.