Regensburg 2013 – scientific programme
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O: Fachverband Oberflächenphysik
O 61: Organic Electronics and Photovoltaics I (jointly with CPP, DS, and HL)
O 61.3: Talk
Thursday, March 14, 2013, 10:15–10:30, H34
Influence of nanostructural changes on the charge carrier dynamics in PTB7 based solar cells — •Andreas Zusan1, Andreas Baumann2, Jens Lorrmann1, Carsten Deibel1, and Vladimir Dyakonov1,2 — 1Experimental Physics VI, Julius-Maximilians-University of Würzburg, D-97074 Würzburg — 2Bavarian Centre for Applied Energy Research e.V. (ZAE Bayern), D-97074 Würzburg
For organic bulk heterojunction solar cells, the blend morphology is one of the most crucial parameters influencing the device performance. Inducing nanostructural changes by means of the use of processing additives is a common practice to increase the power conversion efficiency. Hence, understanding the effect of modified structural properties of organic layers on the charge carrier transport and lifetime is a key issue for further progress in organic photovoltaics. In this context, we applied our novel charge extraction technique OTRACE (Open Circuit Corrected Transient Charge Extraction) to high efficiency solar cells made from the low-bandgap polymer PTB7 in combination with PC70BM using the solvent additive diiodooctane (DIO). The results show two different nongeminate decay regimes identified as a fast direct recombination of free polarons and a trap assisted decay. We find that the DIO induced alteration of the morphology significantly reduces the recombination order of the first regime, whereas it has no influence on the second part arising from the delayed emission of trapped charges. Our explanation based on a multiple-trapping-and-release approach clarifies the large impact of phase separation on charge carrier dynamics.