Dresden 2017 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 47: Organic Photovoltaics and Electronics I (joined session with CPP)

HL 47.5: Vortrag

Mittwoch, 22. März 2017, 10:30–10:45, POT 81

Fast Organic Near-Infrared Photo-Detectors Based on Charge-Transfer Absorption — •Sascha Ullbrich, Bernhard Siegmund, Andreas Mischok, Andreas Hofacker, Donato Spoltore, Christian Körner, Karl Leo, and Koen Vandewal — Dresden Integrated Center for Applied Physics and Photonic Materials (IAPP), Technische Universität Dresden, Dresden, Germany

In this work, we present organic near-infrared photo-detectors based on the absorption of charge-transfer states between ZnPc as donor and C₆₀ as acceptor material. By using a resonant optical cavity device architecture, we reach external quantum efficiencies above 1% at 1064nm for ZnPc:C₆₀ blends, well below (>200nm) the optical gap of the neat materials. We measure transient photo-current (TPC) responses at wavelengths of 355nm, 532nm, and 1064nm, exciting dominantly C₆₀, ZnPc, or the ZnPc-C₆₀ CT state, respectively, and obtain rise and fall times of a few nanoseconds at short circuit. We find that the response upon CT excitation is at least as fast as upon ZnPc or C₆₀ excitation, emphasizing the possibility to generate fast free carriers by intermolecular absorption. By reducing the active area of the devices, we are able to overcome the generally high RC time limitations caused by thin organic layers. The current transients are modeled with time dependent drift-diffusion simulations of electrons and holes which reconstruct the photo-current signal, including capacitance and series resistance effects. The hole mobility of the donor material is identified as the limiting factor for the high frequency response.