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HL: Fachverband Halbleiterphysik

HL 60: Organic Electronics and Photovoltaics IV: OPV

HL 60.9: Vortrag

Mittwoch, 22. März 2017, 17:30–17:45, ZEU 260

On the Role of Triplet Excitons in Organic Solar Cells — •Andreas Sperlich¹, Stefan Väth¹, Hannes Kraus¹, and Vladimir Dyakonov^1,2 — ¹Experimental Physics VI, Julius Maximilian University of Würzburg, 97074 Würzburg — ²Bayerisches Zentrum für Angewandte Energieforschung (ZAE Bayern), 97074 Würzburg

A strategy for increasing the conversion efficiency of organic photovoltaics has been to increase V_OC by tuning the energy levels of donor and acceptor components. However, this opens up a new loss pathway from an interfacial charge transfer state (CTS) to a donor triplet exciton (TE) state called electron back transfer (EBT), which is detrimental to device performance. To test this hypothesis, we study triplet formation in high performing blends of the fullerene PC₇₀BM with either the polymer PTB7 [1] or the soluble small molecule p-DTS(FBTTh₂)₂ [2] and determine the impact of the morphology-optimizing additive 1,8-diiodoctane (DIO). Using photoluminescence and spin-sensitive optically and electrically detected magnetic resonance (ODMR, EDMR) measurements we find that TE formation does not only depend on the materials’ energetics, but also on temperature and nano-morphology. Furthermore, we observe TEs in real devices under realistic working conditions even for the most efficient solar cells, which has implications not only for efficiency, but also for devices stability.

[1] H. Kraus, et al., Sci. Reps. 6, 29158 (2016)

[2] S. Väth, et al., Adv. Energy Mater., doi: 10.1002/aenm.201602016 (2016)