TetrafluoroborateāInduced Reduction in Defect Density in Hybrid Perovskites through Halide Management
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Abstract: Hybridāperovskiteābased optoelectronic devices are demonstrating unprecedented growth in performance, and defect passivation approaches are highly promising routes to further improve properties. Here, the effect of the molecular ion BF4ā, introduced via methylammonium tetrafluoroborate (MABF4) in a surface treatment for MAPbI3 perovskite, is reported. Optical spectroscopy characterization shows that the introduction of tetrafluoroborate leads to reduced nonāradiative chargeācarrier recombination with a reduction in firstāorder recombination rate from 6.5 Ć 106 to 2.5 Ć 105 sā1 in BF4āātreated samples, and a consequent increase in photoluminescence quantum yield by an order of magnitude (from 0.5 to 10.4%). 19F, 11B, and 14N solidāstate NMR is used to elucidate the atomicālevel mechanism of the BF4ā additiveāinduced improvements, revealing that the BF4ā acts as a scavenger of excess MAI by forming MAIāMABF4 cocrystals. This shifts the equilibrium of iodide concentration in the perovskite phase, thereby reducing the concentration of interstitial iodide defects that act as deep traps and nonāradiative recombination centers. These collective results allow us to elucidate the microscopic mechanism of action of BF4ā.
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Funder: Royal SocietyāSERB Newton International Fellowship
Funder: European Union's Horizon 2020 research and innovation program
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1521-4095
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EPSRC (EP/R023980/1)
Marie SkÅodowskaāCurie (841136)
Royal Society (RP/R1/180147)
UK Royal Academy of Engineering (CiET1819_24)
EPSRC (EP/N004272/1, EP/P007767/1)
Engineering and Physical Sciences Research Council (EP/P007767/1)
H2020 Marie SkÅodowskaāCurie Actions (841136)
European Research Council (756962)