Effect of Encapsulation and Light-Soaking on Charge Transport Properties in Organic Semiconductor-Based Diodes

Abstract

Organic semiconductors (OSs) are gaining attention due to their processability, optical and electrical tunability, and cost-effectiveness. This class of materials is most suitable for flexible electronics and bioelectronics, especially when processed in a solution with inorganic or hybrid materials. However, the charge mobility within these materials is impeded by structural and energetic disorder caused by defects that ‘trap’ the charge carriers. The physical locations of the traps and their distribution of energies dictate the charge transport in a device. The present work probes both the interface and bulk defect-states in polymer-based diodes. Tests were performed on the polymers P3HT, MDMO:PPV and PCDTBT. Various techniques were used to record steady-state current-voltage (I-V), transients of CELIV (Charge Extraction by Linearly Increasing Voltage), DiTC (Dark-injection Transient Current) and the photoluminescence of encapsulated and unencapsulated polymer-based diodes, as well as electroluminescence from encapsulated polymer-based diodes. This study also observes the effects of ultra-violet light-soak on these devices. Charge transport dynamics were investigated over a wide time range, and at both microscopic and macroscopic scales. Results from the encapsulated and unencapsulated devices were compared in order to determine the impact of exposure to air. The cathode’s work function decreased during the light-soak, possibly due to UV-induced oxygen desorption from the polymer-cathode interface.