Mapping Photoluminescence Heterogeneity in Tin Halide Perovskite Solar Cells
Robert Westbrook a, Margherita Taddei a, Rajiv Giridharagopal a, Meihuizi Jiang b, Shaun Gallagher a, Saif Haque b, David Ginger a
a Department of Chemistry, University of Washington, Seattle, WA, 98195 USA
b Department of Chemistry, Imperial College London, Wood Lane, 80, United Kingdom
Proceedings of Sustainable Metal-halide perovskites for photovoltaics, optoelectronics and photonics (Sus-MHP)
València, Spain, 2022 December 12th - 13th
Organizers: Teresa S. Ripolles and Hui-Seon Kim
Oral, Robert Westbrook, presentation 017
Publication date: 15th November 2022

The power conversion efficiency (~15%) of Sn-based PSCs (Sn-PSCs) has so far lagged behind that of Pb-based PSCs (25.7%). The Achilles heel of Sn perovskites has been the spontaneous oxidation of Sn2+ to Sn4+, which leads to charge trapping and background hole doping [1]. Pioneering work in the field has shown that sublimation, additive treatments, and functionalization with 2D materials can mitigate Sn(II) to Sn(IV) oxidation. 

Photoluminescence (PL) spectroscopy is a powerful tool for understanding photovoltaic materials as the photoluminescence quantum yield (PLQY) is correlated with the non-radiative voltage loss (and thus PCE). While bulk PL has been used to great effect in the field so far, it is limited in that it averages all of the ensemble PL processes occurring throughout the film. PL microscopy on the other hand provides the opportunity to study the microscopic heterogeneity that leads to voltage loss in semiconductors. Indeed, landmark studies have linked microstructural heterogeneity with voltage loss in MAPbI3 [2] and wide-bandgap perovskite compositions relevant to tandem applications [3-5]. This insight has helped inform surface passivation strategies that have pushed the VOC in Pb-based PSCs to unprecedented heights. Remarkably, there are few reports that tackle the issue of microscale heterogeneity in Pb-free PSCs.

In this study, we use a unique microscopy toolkit based on scanning probe microscopy, hyperspectral PL imaging and PL lifetime mapping to establish structure-function relationships between PEA0.2FA0.8SnI4 heterogeneity and device performance. We find (i) strong correlation between local conductance and local photoluminescence; (ii) photoluminescence homogeneity improves with SnF2 treatment, leading to improvements in device PCE; (iii) the photoluminescence intensity of the 3D phases is correlated with their proximity to the 2D (n = 1, n = 2) phases. We expect findings from multi-modal microscopy studies such as this one to inform the further progression of Sn-based PSCs towards >20% efficiency.

[1] Lanzetta, L.; Webb, T.; Zibouche, N; X. Liang, X.; Ding, D.; Min, G.; Westbrook, R. J. E.; Gaggio, B.; Macdonald, T. J.; Islam, M. S.; Haque, S. A. Nat. Commun., 2021, 12, 2021

[2] deQuilettes, D. W.; Vorpahl S. M.; Stranks, S. D.; Nagaoka, H.; Eperon, G. E.; Ziffer, M. E.;, Snaith, H. J.; Ginger, D. S. Science, 2015, 348, 683

[3] Macpherson, S.; Doherty, T. A. S.; Winchester, A. J.; Kosar, S.; Johnstone, D. N.; Chiang, Y. -H.; Galkowski, K.; Anaya, M.; Frohna, K.; Iqbal, A. N.; Nagane, S.; Roose, B.; Andaji-Garmaroudi, Z.; Orr, K. W. P.; Parker, J. E.; Midgley, P. A.; Dani, K. M.; Stranks, S. D. Nature, 2022, 607, 294

[4] Frohna, K.; Anaya, M.; Macpherson, S.; Sung, J.; Doherty, T. A. S.; Chiang, Y. -H.; Winchester, A. J.; Orr, K. W. P.; Parker, J. E.; Quinn, P. D.; Dani, K. M.; Rao, A.; Stranks, S. D. Nature Nanotechnol., 2022, 17, 190

[5] Taddei, M.; Smith, J. A.; Gallant, B. M.; Zhou, S., Westbrook, R. J. E; Shi, Y.; Wang, J.; Drysdale, J. N.; McCarthy, D. P.; Barlow, S. R.; Snaith, H. J.; Ginger, D. S., ACS Energy Letters, 2022, 7, 4265

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