Nanoscale Heterogeneities Limit Optoelectronic Performance in Halide Perovskites
Tiarnan Doherty a, Andrew Winchester b, Stuart Macpherson a, Duncan Johnstone c, Vivek Pareek b, Elizabeth Tennyson a, Sofiia Kosar b, Felix Kosasih c, Miguel Anaya a, Mojtaba Abdi-Jalebi a, Zahra Andaji-Garmaroudi a, E Laine Wong b, Julien Madeo b, Yu-Hsien Chiang a, Ji-Sang Park d, Young-Kwang Jung e, Christopher Petoukhoff b, Giorgio Divitini c, Michael Man b, Caterina Ducati c, Aron Walsh d e, Paul Midgley c, Keshav Dani b, Samuel Stranks a
a Optoelectronics Group, Cavendish Laboratory, University of Cambridge, UK., J.J. Thomson Avenue, Cambridge, United Kingdom
b Femtosecond Spectroscopy Unit, Okinawa Institute of Science and Technology Graduate University, 1919-1 Tancha, Onna-son, Kunigami-gun, Okinawa, Japan
c University of Cambridge, Department of Materials Science and Metallurgy, UK, Cambridge, United Kingdom
d Department of Materials, Imperial College London, United Kingdom, Prince’s Consort Road, South Kensington Campus, London, United Kingdom
e Global E 3 Institute and Department of Materials Science and Engineering, Yonsei University, Seoul 120-749, Korea, Republic of
nanoGe Perovskite Conferences
Proceedings of International Conference on Perovskite Thin Film Photovoltaics and Perovskite Photonics and Optoelectronics (NIPHO20)
Sevilla, Spain, 2020 February 23rd - 25th
Organizer: Hernán Míguez
Oral, Tiarnan Doherty, presentation 011
Publication date: 25th November 2019

Metal halide perovskite materials exhibit exceptional performance characteristics for low-cost optoelectronic applications. Though widely considered defect tolerant materials, perovskites still exhibit a sizeable density of deep sub-gap non-radiative trap states, which create local variations in photoluminescence [1] that fundamentally limit device performance. These trap states have also been associated with light-induced halide segregation in mixed halide perovskite compositions [2] and local strain [3], both of which can detrimentally impact device stability [4]. The origin and distribution of these trap states remains unknown as the optical diffraction-limit does not allow the nature of the traps to be probed on the length scales required. Understanding the nature of these traps will be critical to ultimately eliminate losses and yield devices operating at their theoretical performance limits with optimal stability.

In this talk we outline the distribution and compositional and structural origins of non-radiative recombination sites in (Cs0.05FA0.78MA0.17)Pb(I0.83Br0.17)3 thin films. By combining scanning electron and synchrotron X-Ray microscopy techniques with photoemission electron microscopy (PEEM) measurements we reveal that nanoscale trap clusters are distributed non-homogenously across the surface of high performing perovskite films and that there are distinct structural and compositional fingerprints associated with the generation of these detrimental sites. In addition, our scanning electron diffraction measurements achieve a spatial resolution of 4nm with an accumulated electron dose of only ~6 e/Å2 (over an order of magnitude lower than established tolerable dose limits for metal halide perovskites). We will also explore how this combination of high-resolution and low accumulated dose provides new insights into the pristine crystallography of these materials on the nanoscale; thus helping to answer ongoing open questions such as ‘what truly defines a grain?’ and ‘are grain boundaries beneficial or detrimental to performance’?

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