Dresden 2011 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 8: Poster: Organic Semiconductors

CPP 8.27: Poster

Montag, 14. März 2011, 17:30–19:30, P2

Study of trap charge in bulk heterojunction organic solar cell structures using impedance spectroscopy — •Debdutta Ray, Lorenzo Burtone, Karl Leo, and Moritz Riede — Institut für Angewandte Photophysik, Technische Universität Dresden, 01062 Dresden, Germany

In this study we use impedance spectroscopy to directly observe and estimate the trap charge density in an operating organic solar cell. Since the carrier collection efficiency in an organic solar cell is directly proportional to the electric field present in the device, the electric field may undergo distortion in the presence of space/trap charge thereby affecting the short circuit current and the fill factor. Space charge formed by photogenerated carriers has been observed, albeit indirectly, from photocurrent-voltage (IV) characteristics until now. However, when using IV characteristics, the interpretation depends on the model used. Capacitance, on the other hand, is a direct measure of the spatial distribution of the electric field inside the device. In this work we measure the capacitance as a function of voltage and frequency in solar cells under illumination. The frequency dependence provides information regarding the energetic distribution of the trap charge. The voltage dependence yields estimation of the trap charge concentration. From experiments, we estimate the lower limit of the trap charge concentration to be approximately 6x10^16 cm^-3 in ZnPc/C60 bulk heterojunction solar cells. The photocurrent-voltage characteristics of the devices can be explained with the capacitance response and the data complements each other.