Berlin 2018 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 78: Hybrid and Perovskite Photovoltaics II

CPP 78.1: Talk

Friday, March 16, 2018, 09:30–09:45, C 264

Trap State Dynamics and Phase Transition in MAPbI3 — Tobias Seewald, Carola Ebenhoch, Susanne Birkhold, and •Lukas Schmidt-Mende — University of Konstanz

Perovskite semiconductors are a new class of semiconductors, significantly different from organic and also inorganic semiconductors. For efficient charge carrier gtobiaseneration, it is essential to minimize non-radiative recombination that can be initiated by energetic trap states. For this purpose, we have studied polycrystalline methylammonium lead iodide perovskite films with varying crystal sizes. Morphology and crystallinity have been modified by means of methylamine gas induced defect healing. Time-resolved photoluminescence as well as pump-probe spectroscopy have been applied in order to relate trap state distribution with crystal sizes and grain boundaries. In this study we can demonstrate the importance of large crystal grains, which allow high carrier mobilities and reduced non-radiative losses that are crucial for efficient solar cell devices. Furthermore, we have investigated the mechanism of the orthorhombic to tetragonal phase transition in MAPbI3 and the resulting changes in material properties. We present experimental evidence for a transient intermediate phase in MAPbI3 that occurs prior to the phase transition into the tetragonal phase, which might be induced by an increasing liberation/polarization of the organic cation within the orthorhombic phase at low temperatures. Our results demonstrate that this phase transition has strong impact on solar cell performance parameters.