Berlin 2012 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 38: [DS] Organic electronics and photovoltaics: electronic properties I (jointly with CPP, HL, O)
O 38.4: Vortrag
Mittwoch, 28. März 2012, 10:15–10:30, H 2032
Investigation of the degradation processes in small molecule solar cells using impedance spectroscopy — •André Döring, Lorenzo Burtone, Martin Hermenau, Karl Leo, and Moritz Riede — Institut für Angewandte Photophysik, Technische Universität Dresden, 01062 Dresden, Germany
The purpose of this work is to correlate the impedance spectra (IS) of different solar cell structures - composed of small molecules - with the degradation processes that take place under different aging conditions.
The materials chosen for the optically active bulk-heterojunction layer are ZnPc as donor and C60 as acceptor, often used in small-molecule solar cells. In addition to the bulk-heterojunction, doped electron and hole transport layers forming a p-i-n structure are used. Concomitant with the measurement of the IS, the characteristic parameters of the device (i.e. jsc, Voc, FF, PCE, EQE) are monitored during the degradation and correlated to the changes in the IS.
Analyzing the IS gives the possibility to identify different electrical processes that take place in the device. At the beginning of the aging process, we observe an initial improvement of the solar cell parameters, in conjunction with a decreasing trap response in the IS spectra. To investigate in more details the role of trap states for the solar cell performance, simplified structures are prepared. We identify in this way the trap location, type and density inside the solar cell structure. The devices are also exposed to controlled atmospheric conditions to investigate whether oxygen or water vapor is more responsible for the observed change in the electrical properties of the solar cell.