TITLE: Materials Studies of New High Efficiency Perovskite Solar Absorbers
Tuesday, April 19th, 2016 11:30 AM – 1:00 pm
Texas Instruments (TI) Auditorium E-1
2900 Semiconductor Drive
Santa Clara, CA
Admission FREE ($5 donation requested). Please register here.
Organic-inorganic halide perovskite films (e.g., methylammonium lead iodide or CH3NH3PbI3) were first employed as light absorbing layers in photovoltaic (PV) devices in 2009, and produced relatively modest power conversion efficiencies (PCEs) of 3.8%.Since then, the development of perovskite solar cells has been meteoric, with PCEs increasing from 3.8% to over 21% in just over five years.
The combination of high extinction coefficients, long charge carrier diffusion lengths and compatibility with low cost, solution-based fabrication processes gives these materials enormous commercial potential.
A significant appeal of CH3NH3PbI3 is their facile synthesis using solution processes. Typically a low temperature anneal (about 100 °C) is involved in film synthesis with subsequent cooling through the cubic-to-tetragonal phase transition near 65 °C. Since the transition temperature is within the range expected in real world device applications, it is therefore important to understand the structural behavior at this transition and its impact on the device performance.
In order to better understand this phase transition in CH3NH3PbI3 thin films, we have developed the capability for operando synchrotron X-ray diffraction by designing a sample stage for simultaneous, temperature dependent measurement of J-V curves and diffraction. This has allowed us to obtain X-ray diffraction data during the operation of CH3NH3PbI3 devices.
Here I will present detailed structural characterization of the perovskite crystal structure with increasing temperature, including the tetragonal lattice distortion, octahedral rotations associated with the room temperature tetragonal phase, and thermal (disorder) parameters. The impact of these structural changes on the device J-V characteristics will be described and we comment on potential implications for material and device properties.
Michael Toney is head of the Materials Sciences Division and a distinguished staff scientist at the Stanford Synchrotron Radiation Lightsource (SSRL), part of the SLAC National Accelerator Laboratory. He is a pioneer in the use of X-ray diffraction and small angle scattering for the determination of molecular and mesoscale structure of organic and polymeric thin films and for the determination of atomic structure of electrode-electrolyte interfaces. Toney received his BS from Caltech in 1979 and his PhD from the University of Washington in 1983, both in physics. He spend one year as a postdoc at the Risoe National Lab (now DTU) in Denmark, where he participated in some of the first surface X-ray diffraction experiments. He then began working at IBM Almaden Research in materials sciences. He left IBM in 2003 to join SLAC National Accelerator Laboratory and Stanford, where he starting programs in sustainable energy materials.
- 11:30 am – Registration & light lunch (pizza & drinks)
- Noon – Presentation & Questions/Answers
- 1:00 pm – Adjourn
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