Berlin 2018 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 61: Focus: Fundamental Physics of Perovskites II - organized by Lukas Schmidt-Mende and Vladimir Dyakonov
CPP 61.9: Vortrag
Donnerstag, 15. März 2018, 12:15–12:30, C 130
Surface State Density Determines the Energy Level Alignment at Hybrid Perovskite/Electron Acceptor Interfaces — •Fengshuo Zu1,2, Patrick Amsalem1, Maryline Ralaiarisoa1,2, Thorsten Schultz1, Raphael Schlesinger1,2, and Norbert Koch1,2 — 1Institut für Physik, HU Berlin — 2HZB, 12489 Berlin
Substantial variations of the surface electronic structure and thus conflicting energetics at interfaces between hybrid perovskites and charge transport layers can be found in literature. In an attempt to unravel the origin of these variations, we demonstrate that donor-like surface states stemming from reduced lead (Pb0) directly impact the energy level alignment at perovskite and molecular electron acceptor interfaces, using photoelectron spectroscopy. When forming the interfaces, it is found that electron transfer from surface states to acceptor molecules occurs, leading to a strong decrease in the density of ionized surface states. As a consequence, for perovskites with low surface state density, the initial band bending at the pristine perovskite surface can be flattened upon interface formation. In contrast, for perovskites with a high surface state density, the Fermi-level is strongly pinned at the conduction band edge and only minor changes in surface band bending are observed upon acceptor deposition. Consequently, depending on the initial surface state density, very different interface energy level alignment situations (variations over 0.5 eV) are demonstrated and rationalized. Our findings help explaining the rather dissimilar reported energy levels at interfaces and refining our understanding of the operating principles in devices comprising this material.