Thesis presented December 15, 2016

Abstract:
Over the past few years, great improvement has been made in organic, polymer-based devices performances. Unfortunately, problems with their stabilities still persist, constraining the use of costly encapsulations. In operating conditions, photodiodes are exposed to many stresses, reducing their lifetime: light (UV-visible), water, oxygen, temperature, electrical bias or even mechanical stress. These various factors lead to the progressive deterioration of polymers used in devices that induce degradations and performances losses. Hence, unravelling the physics behind the degradation mechanisms is needed in order to improve their stability. Most importantly, it is crucial to understand the role of each factor (such as oxygen, light, water) in degrading the performances of the devices. In this work we aim to decorrelate the influence of the different ageing effects by investigating the impact of environment and light on electrical characteristics of operating photodiodes. For this purpose, different photodiodes ageing have been performed in dark, under light and in different atmospheres such as inert gas, dry air, and ambient air. Scenario could be proposed to explain the degradation based on the analysis of the device figures of merit of the device and numerical simulations. Finally, complementary electrical and chemical characterizations have been performed in order to highlight the degradation mechanisms. We show that oxygen induces traps in the bandgap of the active layer that reduces photocurrent and increases charges injection and capacitance.

Keywords:
Gap states, Reliability, Modelling, Photodiodes, Aging, Organic electronics

On-line thesis.