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HL: Fachverband Halbleiterphysik

HL 68: Photovoltaics: Organic Semiconductors

HL 68.3: Vortrag

Mittwoch, 28. März 2012, 18:15–18:30, ER 270

Field dependence of charge carrier generation in MDMO-PPV based organic solar cells — •Julia Kern¹, Clemens Grünewald¹, Carsten Deibel¹, and Vladimir Dyakonov^1,2 — ¹Experimental Physics VI, Julius Maximilian University of Würzburg, D-97074 Würzburg — ²ZAE Bayern, D-97074 Würzburg

One of the key issues of organic photovoltaics is the fundamental understanding of charge photogeneration and recombination. The dissociation of the singlet excitons created in the polymer is likely to occur via one of two distinct routes, the first one being direct dissociation to free charge carriers and the second one involving an intermediate step comprising the formation of an interfacial charge transfer exciton (CTE). In order to shed light onto the relevance of the respective dissociation patterns, we investigated the field dependence of CTE photoluminescence as a means of probing geminate recombination as well as of the photocurrent, being a direct indicator for free charge carriers. Starting with MDMO-PPV blended with PCBM as a reference system, we employed various fullerene derivatives, systematically changing the lowest unoccupied molecular orbital (LUMO) and thus the open circuit voltage, correspondingly. This approach allows us to study the influence of the different parameters on the CTE binding energy, which can be derived from the dissociation probability predicted by the Onsager Braun model. In view of our results, we discuss the correlation between this binding energy and the field dependent charge generation.