Electrical defects in m-MTDATA studied using charge transient spectroscopy

Organic electronics is an emerging technology which has received great attention in past decades due to their potential applications in the next generation electronic devices such as Organic Solar Cells, Thin Film Transistors, Organic Light Emitting Diodes. These devices are made using cost-effective materials, suitable for the low temperature processing, compatible with sustainable and easily scalable processing techniques. Degradation being the major issue, specifically roles of traps in such devices is being studied extensively to enhance the performance. In this study, charge transient spectroscopy is utilized to investigate the trap states in the prototypical small molecule 4, 40, 400-tris(N-3-methylphenyl-N-phenyl-amino) triphenyl-amine (m-MTDATA) based organic diodes. The trap levels have been resolved using the emission kinetics with time resolved spectroscopic analysis technique on charge transients. Varied pulses with different bias and time was applied across device to study the carrier capture kinetics. Temperature dependent measurements were also performed to isolate the trap levels. We found that initial peak is due to displacement current of the device which is related to the transport mechanism of the device. We show that the amplitude of signal is dependent on the amount of charge injected which depends on the combination of time and the bias applied. Various observed trap levels are identified based on the emission time constants but their contribution in the emission kinetics is insignificant, indicating that the amount of trap levels are very small. Charge redistribution in the trap levels was observed at higher charging time. (C) 2020 Elsevier Ltd. All rights reserved.