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. 2019 Oct;31(42):e1902374.
doi: 10.1002/adma.201902374. Epub 2019 Sep 6.

A Highly Emissive Surface Layer in Mixed-Halide Multication Perovskites

Zahra Andaji-Garmaroudi  1 , Mojtaba Abdi-Jalebi  1 , Dengyang Guo  2 , Stuart Macpherson  1 , Aditya Sadhanala  1   3 , Elizabeth M Tennyson  1 , Edoardo Ruggeri  1 , Miguel Anaya  1 , Krzysztof Galkowski  1   4 , Ravichandran Shivanna  1 , Kilian Lohmann  1 , Kyle Frohna  1 , Sebastian Mackowski  4 , Tom J Savenije  2 , Richard H Friend  1 , Samuel D Stranks  1
Affiliations

A Highly Emissive Surface Layer in Mixed-Halide Multication Perovskites

Zahra Andaji-Garmaroudi et al. Adv Mater. 2019 Oct.

Abstract

Mixed-halide lead perovskites have attracted significant attention in the field of photovoltaics and other optoelectronic applications due to their promising bandgap tunability and device performance. Here, the changes in photoluminescence and photoconductance of solution-processed triple-cation mixed-halide (Cs0.06 MA0.15 FA0.79 )Pb(Br0.4 I0.6 )3 perovskite films (MA: methylammonium, FA: formamidinium) are studied under solar-equivalent illumination. It is found that the illumination leads to localized surface sites of iodide-rich perovskite intermixed with passivating PbI2 material. Time- and spectrally resolved photoluminescence measurements reveal that photoexcited charges efficiently transfer to the passivated iodide-rich perovskite surface layer, leading to high local carrier densities on these sites. The carriers on this surface layer therefore recombine with a high radiative efficiency, with the photoluminescence quantum efficiency of the film under solar excitation densities increasing from 3% to over 45%. At higher excitation densities, nonradiative Auger recombination starts to dominate due to the extremely high concentration of charges on the surface layer. This work reveals new insight into phase segregation of mixed-halide mixed-cation perovskites, as well as routes to highly luminescent films by controlling charge density and transfer in novel device structures.

Keywords: halide perovskites; luminescence; passivation; photoinduced ion migration; time-resolved spectroscopy.

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