The varied nature and roles of nanoscale defects in solution processed triple cation mixed halide perovskite thin films

Sofiia Kosar^a, Andrew J. Winchester^a, Tiarnan A. S. Doherty^b, Stuart Macpherson^b, Christopher E. Petoukhoff^a, Kyle Frohna^b, Miguel Anaya^b^,^c, Nicholas S. Chan^a, Julien Madéo^a, Michael K. L. Man^a, Samuel D. Stranks^b^,^c, Keshav M. Dani^a

^aFemtosecond Spectroscopy Unit, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa, 904 0495, Japan

^bCavendish Laboratory University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK

^cDepartment of Chemical Engineering and Biotechnology, University of Cambridge, Philippa Fawcett Drive, Cambridge CB3 0AS, UK

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV22)

València, Spain, 2022 May 19th - 25th

Organizers: Pablo Docampo, Eva Unger and Elizabeth Gibson

Oral, Sofiia Kosar, presentation 071
DOI: https://doi.org/10.29363/nanoge.hopv.2022.071
Publication date: 20th April 2022

Despite the rapid progress that hybrid perovskite solar cells have demonstrated during the past decade, much remains unknown about the processes that limit their performance and viability. In particular, the properties of perovskite absorbers require thorough research, especially for mixed compositions that have been employed for devices with highest efficiencies and have potential for applications in tandem technologies. Such perovskite films have been reported to have multiple scales of heterogeneities [1], some of which have been associated with presence of charge trapping defects that place substantial limitations on performance of perovskites [2, 3,4]. The fundamental understanding of these defects, in particular about their formation sites, and direct impact on device efficiency, is important for designing successful passivation strategies to improve performance and viability of perovskite photovoltaics.

In this work, we take a closer look at defect-mediated processes by directly visualizing defects and their spatio-temporal charge trapping dynamics. We employed photoemission electron microscopy to directly image nanoscale defects that form in solution processed perovskite films [2] and revealed their spatial arrangement with respect to surface microstructure. By adding time resolution to our photoemission experiments, we accessed the exact roles of these defects in performance of perovskite thin films by monitoring charge trapping processes that occur at defect-rich sites. We found that depending on their origin, these nanoscale defects play very different roles in photoexcited hole trapping – from very detrimental to relatively benign [5]. Our results shed more light on defect structure of perovskites and highlight the need to develop targeted approaches to remove each undesired type of defect.

References:

[1] Tennyson E. et al., Heterogeneity at Multiple Length Scales in Halide Perovskite Semiconductors. Nat. Rev. Mater. 2019, 4, 573-587.

[2] deQuilettes et al., Photo-Induced Halide Redistribution in Organic-Inorganic Perovskite Films, Nat. Commun. 2016, 7, 11683.

[3] Jones T. W. et al. Lattice Strain Causes Non-Radiative Losses in Halide Perovskites. Energy Environ. Sci. 2019, 12, 596-606.

[4] Doherty, T. A. S.; Winchester, A. J. et al. Performance-Limiting Nanoscale Trap Clusters at Grain Junctions in Halide Perovskites. Nature 2020, 580, 360–366.

[5] Kosar S. et al., Unraveling the Varied Nature and Roles of Defects in Hybrid Halide Perovskites with Time-Resolved Photoemission Electron Microscopy. Energy Environ. Sci. 2021, 14, 6320-6328.

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