Regensburg 2022 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 41: Organic Semiconductors 2

HL 41.4: Talk

Friday, September 9, 2022, 10:15–10:30, H34

Experimental and theoretical studies of the occupied density of states distribution of charge carriers at low temperatures in disordered organic semiconductors — •Andrei Stankevych, Rishabh Saxena, Heinz Bässler, Andrey Kadashchuk, and Anna Köhler — Soft Matter Optoelectronics and Bavarian Polymer Institute (BPS), Universitätsstrasse 30, 95448 Bayreuth, Germany

The thermally-stimulated luminescence (TSL) technique has been applied to determine the width of density of state (DOS) distribution σ _DOS in pristine amorphous films of 18 common OLED materials. The high-temperature wing of the TSL curve in amorphous materials is an exact replica of the deeper portion of the DOS distribution and yields the effective DOS width. In addition, we measured the width of the TSL curves σ _TSL and found that it scales linearly with σ _DOS parameter, suggesting an existence of a universal ratio σ _TSL / σ _DOS ≈ 2/3 observed for a large set of organic materials. The low-temperature energy relaxation of photogenerated carriers within a Gaussian DOS implies a significant narrowing of the ODOS distribution. In order to gain a deeper insight into this effect, we performed extensive Monte- Carlo simulations of charge-carrier energetic relaxation process and found that such "spectral narrowing" effect is a genuine property of the hopping carrier relaxation at low temperature within a Gaussian DOS. Moreover, we found that spatial energy correlation effects, which are indeed present in organic media, must be considered for the quantitative description of experimental observations.