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Comparing the excited-state properties of a mixed-cation–mixed-halide perovskite to methylammonium lead iodide

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  • Jan C. Brauer
  • Demetra Tsokkou
  • Sandy Sanchez
  • Nikolaos Droseros
  • Bart Roose
  • Edoardo Mosconi
  • Xiao Hua
  • Martin Stolterfoht
  • Dieter Neher
  • Ullrich Steiner
  • Filippo De Angelis
  • Antonio Abate
  • Natalie Banerji
Article number104703
<mark>Journal publication date</mark>14/03/2020
<mark>Journal</mark>Journal of Chemical Physics
Issue number10
Number of pages9
Publication StatusPublished
Early online date9/03/20
<mark>Original language</mark>English


Organic–inorganic perovskites are one of the most promising photovoltaic materials for the design of next generation solar cells. The lead-based perovskite prepared with methylammonium and iodide was the first in demonstrating high power conversion efficiency, and it remains one of the most used materials today. However, perovskites prepared by mixing several halides and several cations systematically yield higher efficiencies than “pure” methylammonium lead iodide (MAPbI3) devices. In this work, we unravel the excited-state properties of a mixed-halide (iodide and bromide) and mixed-cation (methylammonium and formamidinium) perovskite. Combining time-resolved photoluminescence, transient absorption, and optical-pump–terahertz-probe experiments with density functional theory calculations, we show that the population of higher-lying excited states in the mixed material increases the lifetime of photogenerated charge carriers upon well above-bandgap excitation. We suggest that alloying different halides and different cations reduces the structural symmetry of the perovskite, which partly releases the selection rules to populate the higher-energy states upon light absorption. Our investigation thus shows that mixed halide perovskites should be considered as an electronically different material than MAPbI3, paving the way toward further materials optimization and improved power conversion efficiency of perovskite solar cells.