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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 76: Organic semiconductors II (joint session HL/CPP)

CPP 76.7: Vortrag

Mittwoch, 18. März 2020, 17:15–17:30, POT 112

Reverse Dark Current in Organic Photodetectors — •Jonas Kublitski¹, Andreas Hofacker¹, Christina Kaiser², Donato Spoltore¹, Hans Kleemann¹, Axel Fischer¹, Koen Vandewal³, and Karl Leo¹ — ¹IAPP - TU Dresden, Germany — ²Swansea University, UK — ³IMO - Hasselt University, Belgium

Photodetectors (PDs) find broad applications in many fields of optics. While inorganic PDs are widely used, they lack in easy processability and narrow-band detection. Organic PDs can fulfill these demands, providing many further advantages in comparison to inorganic PDs. The limiting factor of OPDs is their low detectivity, mostly caused by high dark current (J_D) at reverse bias. Traps and sub-gap states are often observed in organic materials. Here, we investigate their effect on J_D. We observe that J_D follows a trend with the energies of the sub-gap CT states (E_CT). Furthermore, in specific donor:C₆₀ blends, we find trap concentrations of around 10¹⁶ cm⁻³ with an energy of around 0.5 eV below the transport level of C₆₀. We intentionally vary the trap concentration in these blends and observe that*J_D scales accordingly. Dark current-voltage simulations show that the expected value of*J_D increases four orders of magnitude and rules the dark JV characteristics, when traps are included. The dependence of J_D on reverse bias can be understood as an enhanced detrapping by means of Poole-Frenkel effect. These results point out to a physical process that might be general in donor:acceptor structures, explaining the high*J_D commonly observed in OPDs. Moreover, optimized devices show J_D as low as 500 pA cm⁻² at -1 V, and on/off ratio of 10⁷.