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Instruments / Technical Area	Publication Details	Published	Actions
E02-JEM ARM 300CF I14-Hard X-ray Nanoprobe	Performance-limiting nanoscale trap clusters at grain junctions in halide perovskites Tiarnan A. S. Doherty , Andrew J. Winchester , Stuart Macpherson , Duncan N. Johnstone , Vivek Pareek , Elizabeth M. Tennyson , Sofiia Kosar , Felix U. Kosasih , Miguel Anaya , Mojtaba Abdi-jalebi , Zahra Andaji-garmaroudi , E. Laine Wong , Julien Madéo , Yu-hsien Chiang , Ji-sang Park , Young-kwang Jung , Christopher E. Petoukhoff , Giorgio Divitini , Michael K. l. Man , Caterina Ducati , Aron Walsh , Paul A. Midgley , Keshav M. Dani , Samuel D. Stranks Nature 580, 360 - 366 DOI: 10.1038/s41586-020-2184-1 Diamond Proposal Number(s): [19023, 19793] Show Abstract ▼ Abstract: Halide perovskite materials have promising performance characteristics for low-cost optoelectronic applications. Photovoltaic devices fabricated from perovskite absorbers have reached power conversion efficiencies above 25 per cent in single-junction devices and 28 per cent in tandem devices. This strong performance (albeit below the practical limits of about 30 per cent and 35 per cent, respectively) is surprising in thin films processed from solution at low-temperature, a method that generally produces abundant crystalline defects. Although point defects often induce only shallow electronic states in the perovskite bandgap that do not affect performance, perovskite devices still have many states deep within the bandgap that trap charge carriers and cause them to recombine non-radiatively. These deep trap states thus induce local variations in photoluminescence and limit the device performance. The origin and distribution of these trap states are unknown, but they have been associated with light-induced halide segregation in mixed-halide perovskite compositions and with local strain, both of which make devices less stable. Here we use photoemission electron microscopy to image the trap distribution in state-of-the-art halide perovskite films. Instead of a relatively uniform distribution within regions of poor photoluminescence efficiency, we observe discrete, nanoscale trap clusters. By correlating microscopy measurements with scanning electron analytical techniques, we find that these trap clusters appear at the interfaces between crystallographically and compositionally distinct entities. Finally, by generating time-resolved photoemission sequences of the photo-excited carrier trapping process, we reveal a hole-trapping character with the kinetics limited by diffusion of holes to the local trap clusters. Our approach shows that managing structure and composition on the nanoscale will be essential for optimal performance of halide perovskite devices.	Apr 2020
E02-JEM ARM 300CF	Heterogeneity at multiple length scales in halide perovskite semiconductors Elizabeth M. Tennyson , Tiarnan A. S. Doherty , Samuel D. Stranks Nature Reviews Materials 44 DOI: 10.1038/s41578-019-0125-0 Diamond Proposal Number(s): [19793] Show Abstract ▼ Abstract: Materials with highly crystalline lattice structures and low defect concentrations have classically been considered essential for high-performance optoelectronic devices. However, the emergence of high-efficiency devices based on halide perovskites is provoking researchers to rethink this traditional picture, as the heterogeneity in several properties within these materials occurs on a series of length scales. Perovskites are typically fabricated crudely through simple processing techniques, which leads to large local fluctuations in defect density, lattice structure, chemistry and bandgap that appear on short length scales (<100 nm) and across long ranges (>10 μm). Despite these variable and complex non-uniformities, perovskites maintain exceptional device efficiencies and are, as of 2018, the best-performing polycrystalline thin-film solar cell material. In this Review, we highlight the multiple layers of heterogeneity ascertained using high-spatial-resolution methods that provide access to the relevant length scales. We discuss the impact that the optoelectronic variations have on halide perovskite devices, including the prospect that it is this very disorder that leads to their remarkable power-conversion efficiencies.	Jul 2019

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