AMaSiS 2018 Workshop: Abstracts

A differential method to analyze arbitrary recombination processes in semiconductor devices

Jinhan Wu, Axel Fischer, and Sebastian Reineke

Dresden Integrated Center for Applied Physics and Photonic Materials

Even though organic light-emitting diodes (OLEDs) have reached the stage of commercialization, a comprehensive understanding of its recombination process is still lacking. One reason is that current-voltage characteristics are often influenced by charge transport and charge injection which prevent a proper analysis regarding recombination. In order to overcome such restrictions in OLEDs, we adapted the illumination intensity versus open-circuit voltage (Suns-$V_{oc}$) method, used for solar cells [1]. Applying this method to a state-of-the-art red-light-emitting OLED at various temperatures, we obtain undisturbed characteristics that can be investigated in great detail.

For that purpose, we developed an evaluation method which yields parameters for arbitrary recombination processes without assuming any model prior. The effective bandgap over which recombination takes place, the hypothetical maximum recombination current density, and the ideality factor are obtained and can be investigated regarding the temperature as well as the excitation dependency [2]. Our approach is based on the fact that locally the temperature and voltage dependent recombination current can be approximated by a homogeneous recombination equation with constant recombination coefficient, realized by a differential evaluation scheme.

Once the parameters are available for various external parameters, the data structure can be analyzed and models developed. For example, we are able to reconstruct the external quantum efficiency versus current density dependency by assigning radiative and non-radiative recombination processes in our model.

In general, our approach quickly provides parameters as needed e.g. for drift-diffusion as well as Monte-Carlo simulations to support the overall modeling and understanding of organic semiconductor diodes.

Acknowledgments: This work was supported in part by the German Research Foundation (DFG) within the Cluster of Excellence Center for Advancing Electronics Dresden (cfaed) and the DFG project “Electrothermal feedback in organic devices” (EFOD, RE 3198/6-1).