Time Scales in Methylammonium Lead Iodide Perovskite Solar aAbsorbers – Michael F Toney

July 5, 2019 @ 2:30 pm – 3:30 pm
Kapitza Seminar Room
Kapitza Building
Cavendish Laboratory
Elizabeth Tennyson

Hybrid organic-inorganic perovskites (HOIPs) have excited the photovoltaic community due to their high light to power conversion efficiencies. In this talk I will show our recent results on the lattice dynamics (fast time scales ≈ps) and on the HOIP formation mechanisms (slow time scales ≈minutes). One of the distinguishing properties of HOIPs compared to conventional semiconductors is the considerable disorder in the lattice that varies over length and time scales. These lattice dynamics are important for both the cooling and transport of photoexcited charge carriers.
In the first part of this talk, I describe our high-precision measurements of acoustic phonon lifetimes in the hybrid perovskite methylammonium lead iodide (MAPbI3) that reveal extremely short lifetimes on the order of picoseconds, corresponding to nanometer mean free paths, showing that acoustic phonons are unable to efficiently dissipate heat. These findings illustrate a fundamental difference between HOIPs and conventional photovoltaic semiconductors. Another surprising aspect of HOIPs is that they are synthesized under mild conditions (e.g., 100°C annealing) and solution processing. I will also discuss the formation of MAPbI3 films from the single-step deposition of lead chloride and three equivalents of methylammonium iodide (PbCl2 + 3CH3NH3I). We use X-ray scattering and absorption to determine the film formation mechanisms, revealing the importance of a self-regulating mechanism that slows the film growth. This provides insight into optimizing processing conditions and realizing enhanced optoelectronic properties in HOIPs.