Dresden 2017 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 19: Fundamentals of Perovskite Photovoltaics III (jointly with CPP/HL)
DS 19.5: Vortrag
Dienstag, 21. März 2017, 10:45–11:00, ZEU 222
Impact of Illumination on the Electronic and Chemical Structure of Mixed Halide Perovskites — •Fengshuo Zu1, Patrick Amsalem1, Ingo Salzmann1, Rongbin Wang1,2, Maryline Ralaiarisoa1, Stefan Kowarik1, Steffen Duhm2, and Norbert Koch1 — 1Institut für Physik,Humboldt-Universität zu Berlin,12489 Berlin,Germany — 2FUNSOM,Soochow-University,Suzhou,China
The seemingly n-type behavior of the perovskite films is largely intriguing since these films are calculated to be bipolar conductive. For exploring the fundamental physics of the n-type behavior, we investigate the effect of white-light illumination on the electronic structure of mixed halide perovskite thin films and of CH3NH3PbI3 single crystals using X-ray and ultraviolet PES, as well as UV-Vis absorption spectroscopy. The samples are found to be strongly n-type and, upon illumination, the valence band features shift by up to 0.7 eV to lower BE. We show this effect to be correlated with initial surface band bending due to the presence of donor levels likely consisting of reduced lead (Pb0) acting as surface traps. Upon short-time illumination, this phenomenon is found to be partially reversible, for prolonged illumination, however, a high concentration of metallic Pb0 is generated inducing strong Fermi-level pinning. This effect is accompanied by the formation of PbI2 defects within the film and a deficiency of iodine in the surface region. Experiments performed on CH3NH3PbI3 single crystal reveal the presence of a relatively high concentration of reduced Pb0 at the sample surface after cleaving, likewise, strongly pinning the Fermi-level even under high intensity illumination.