Séminaire Nano

Mardi 26 Mai 2015 à 11h00.

Growth of complex systems: Organic-organic heterostructures for organic electronics

''Functional organic materials and devices are becoming increasingly complex. Their preparation and growth is, not surprisingly, similarly complex, and the resulting structure will be determined by a competition between kinetics and thermodynamics, which is not trivial to predict in particular for multi-component systems. We discuss general concepts [1] and recent examples [2,3] of organics-based heterostructure growth in the context of kinetic effects compared to thermodynamic (equilibrium) structure. These include unconventional roughening and smoothing behavior at interfaces as well as unconventional structural motifs, such as a frozen-smectic structure formed in a blend of organic semiconductors which form conventional crystals as pure compounds [4]. Particular attention is paid to the case of kinetically limited phase separation of a donor-acceptor pair (DIP:C60) used in organic photovoltaics [5]. This leads to asymmetric domain sizes near bottom vs top electrode due to the time (thickness) dependent phase separation with important implications for device modeling [1,6]. We also discuss the associated optical properties and the question of coupling between donor and acceptor components [7,8]. Finally, we comment on the implications of the structure and morphology for the optical and electronic properties as well as possible device applications with focus on organic photovoltaics [1,6]. Contributions by A. Hinderhofer, C. Frank, K. Broch, F. Anger, J. Novak, R. Banerjee, A. Gerlach, and S. Kowarik, are gratefully acknowledged. [1] A. Hinderhofer and F. Schreiber, ChemPhysChem, 13 (2012) 628 ; A. Dürr et al., Phys. Rev. Lett. 90 (2003) 016104 ; S. Kowarik et al., Phys. Rev. Lett. 96 (2006) 125504 ; S. Bommel et al., Nature Comm. 5 (2014) 5388 [2] A. Hinderhofer et al., J. Phys. Chem. C 115 (2011) 16155 [3] A. Hinderhofer et al., J. Chem. Phys. 134 (2011) 104702 [4] A. Aufderheide et al., Phys. Rev. Lett. 109 (2012) 156102 [5] R. Banerjee et al., Phys. Rev. Lett. (2013) [6] J. Wagner et al., Adv. Funct. Mater. 20 (2010) 4295 [7] K. Broch et al., Phys. Rev. B 83 (2011) 245307 [8] F. Anger et al., J. Chem. Phys. 136 (2012) 054701''