The Effect of Nanoscale Structural and Compositional Heterogeneities on the Photophysical Properties of Triple Cation Perovskite Films
Tiarnan Doherty a, Duncan Johnstone b, Felix Utama Kosasih b, Stuart Macpherson a, Andrew Wincheser c, Giorgio Divitini b, Keshav Dani c, Caterina Ducati b, Paul Midgley b, Sam Stranks a
a Cavendish Laboratory, Department of Physics, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK.
b Department of Materials Science and Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge CB3 0FS, United Kingdom
c Okinawa Institute of Science and Technology (OIST), Okinawa, Japan
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2019 May 12th - 15th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Poster, Tiarnan Doherty, 181
Publication date: 11th February 2019

Metal halide perovskites are exceptional candidates for inexpensive next generation optoelectronic devices. State-of-the-art perovskite photovoltaic devices exhibit performance characteristics approaching that of established thin-film semiconductor technologies (i.e., power conversion efficiencies exceeding 22%), with our passivated embedded semiconductor layers demonstrating > 90% internal photoluminescence quantum efficiency; results that are remarkable given their short development timeframe. This pace of development has been so extraordinary in fact, that empirical device improvements have outpaced the complete physical understanding of the materials. For example, the nature of the defects contributing to non-radiative losses and how they relate to nanoscale structural and compositional heterogeneity remains unclear. Understanding the operating principles of perovskites on the smallest length scales will allow us to fabricate materials approaching their theoretical limits.

In this talk we will detail a multiscale approach to show how structural heterogeneities - such as crystallographic twin domains - and compositional heterogeneities - such as halide segregation - on the nanoscale, effect the electronic properties of (MA,FA,Cs)Pb(I0.8Br0.2)3 thin films. We spatially correlate high resolution nano x-ray diffraction and nano x-ray fluorescence obtained on the I14 nanoprobe beamline at Diamond Light Source, scanning electron diffraction, scanning transmission electron microscopy-energy dispersive x-ray spectroscopy, photoluminescence, and photoemission maps to reveal that strain related structural and compositional defects have a significant impact on the nanoscale and microscale optoelectronic properties of perovskite thin films.

Our work reveals important information on the relevance of defects in the operation of state-of-the-art perovskite optoelectronic devices, which is critical to inform future crystal growth and materials passivation strategies. We also detail correlated multimodal characterisation techniques with nanoscale spatial resolutions that are applicable to inherently beam sensitive materials such as perovskites.

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