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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 38: Fundamentals of Perovskite Photovoltaics V (joint session CPP/DS/HL)

CPP 38.1: Hauptvortrag

Mittwoch, 22. März 2017, 10:15–10:45, ZEU 250

Light-induced degradation of methylammonium and formamidinium PbI3 perovskites — •Norbert H. Nickel, Felix Lang, Victor V. Brus, and Jörg Rappich — Helmholtz-Zentrum Berlin für Materialien und Energie, Institut für Silizium Photovoltaik, Kekuléstr. 5, 12489 Berlin

We investigate the stability of methylammonium (CH3NH3+ - MA) and formamidinium (HC(NH2)2+ - FM) lead iodide perovskite films using visible and ultra violet light in oxygen atmosphere and in vacuum. Insight into the degradation mechanisms was obtained from in-situ Fourier-transform infrared absorption (FT-IR), photoluminescence, and gas effusion measurements. We revisited the light-induced degradation of MAPbI3 in the presence of oxygen. Illumination in O2 atmosphere results in a swift degradation. Isotope experiments clearly show that O2 acts as a catalyst decomposing MA ions into CH3NH2 and hydrogen. In case of FMPbI3 perovskites illumination in the presence of O2 results in a more complex reaction; decomposition of the FM ions occurs at the N-C-N bonds and as a result CO2 and C = O molecules are formed that rapidly diffuse out of the crystalline lattice.

In addition, we present experimental evidence of a hitherto unknown but fundamental degradation mechanism of MAPbI3 and FMPbI3 perovskite layers due to exposure to visible and ultra violet light. This degradation mechanism does not require the presence of oxygen or other constituents. Our data indicate that the molecular orbitals of the organic ions are not in resonance with the energy bands of the perovskite.