Electrostatics of Interfaces In Hybrid Organic-Inorganic and Nanostructured Solar Cells

Tejas Sherkar^a, Jan Anton Koster^a

^aUniversity of Groningen, The Netherlands, Nijenborgh, 4, Groningen, Netherlands

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Roma, Italy, 2015 May 11th - 13th

Organizer: Filippo De Angelis

Oral, Tejas Sherkar, presentation 210
Publication date: 5th February 2015

Dielectric interfaces are universal in solar cells and are central to the device performance as they are active sites for generation and recombination of charge carriers. The hypotheses for charge carrier recombination include the pinning down of the charge carrier at the interface via coulomb interaction as a result of the contrast in relative permittivity (or the dielectric constant) of the materials forming the interface [1,2]. Electrostatic polarization in presence of the contrast is known to give rise to induced surface charges on the interface. Here, we embark on a theoretical approach to understand the electrostatic effects due to induced charges on interfaces which are known to influence the local charge dynamics during device operation.Due to the high contrast in the relative permittivity (ε) between materials used in hybrid organic/inorganic (OI) devices, these systems serve as an ideal platform to study the modified electrostatic effects due to the presence of a dielectric interface. We consider a charge separation scenario across the interface and calculate the binding energy of the charge carrier for variations in the interfacial factors as described below. We find that the high dielectric contrast (ε_I/ε_O> 20) is responsible for binding of the charge carrier with energies above 2 kT. For the variation in interface shape and size (both defined by the morphology), we show that assumption of the planar interface (infinitely long) overestimates the attractive potential. The change in the interface curvature (defined by the local shape and size) affects the binding energy of the charge carrier by order of kT. Anisotropy is shown to critically affect the electrostatic force along the principal axis, while the binding energy of the charge is altered by more than 5 kT. We are able to give an upper limit on the change in the binding energy for the variations in the above interfacial factors. These limits can serve as guidelines for optimization, interface engineering and design of high efficiency solar cells.

[1] Graetzel, M.; Janssen, R. a J.; Mitzi, D. B.; Sargent, E. H. Materials interface engineering for solution-processed photovoltaics. Nature 2012, 488, 304–312. [2] Noone, K. M.; Subramaniyan, S.; Zhang, Q.; Cao, G.; Jenekhe, S. A.; Ginger, D. S. Photoinduced Charge Transfer and Polaron Dynamics in Polymer and Hybrid Photovoltaic Thin Films: Organic vs Inorganic Acceptors. J. Phys.Chem. C 2011, 115, 24403–24410.

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