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Targeted Ligand-Exchange Chemistry on Cesium Lead Halide Perovskite Quantum Dots for High-Efficiency Photovoltaics
journal contribution
posted on 2018-07-25, 00:00 authored by Lance M. Wheeler, Erin M. Sanehira, Ashley R. Marshall, Philip Schulz, Mokshin Suri, Nicholas C. Anderson, Jeffrey A. Christians, Dennis Nordlund, Dimosthenis Sokaras, Thomas Kroll, Steven P. Harvey, Joseph J. Berry, Lih Y. Lin, Joseph M. LutherThe
ability to manipulate quantum dot (QD) surfaces is foundational
to their technological deployment. Surface manipulation of metal halide
perovskite (MHP) QDs has proven particularly challenging in comparison
to that of more established inorganic materials due to dynamic surface
species and low material formation energy; most conventional methods
of chemical manipulation targeted at the MHP QD surface will result
in transformation or dissolution of the MHP crystal. In previous work,
we have demonstrated record-efficiency QD solar cells (QDSCs) based
on ligand-exchange procedures that electronically couple MHP QDs yet
maintain their nanocrystalline size, which stabilizes the corner-sharing
structure of the constituent PbI64– octahedra
with optoelectronic properties optimal for solar energy conversion.
In this work, we employ a variety of spectroscopic techniques to develop
a molecular-level understanding of the MHP QD surface chemistry in
this system. We individually target both the anionic (oleate) and
cationic (oleylammonium) ligands. We find that atmospheric moisture
aids the process by hydrolysis of methyl acetate to generate acetic
acid and methanol. Acetic acid then replaces native oleate ligands
to yield QD surface-bound acetate and free oleic acid. The native
oleylammonium ligands remain throughout this film deposition
process and are exchanged during a final treatment step employing
smaller cationsnamely, formamidinium. This final treatment
has a narrow processing window; initial treatment at this stage leads
to a more strongly coupled QD regime followed by transformation into
a bulk MHP film after longer treatment. These insights provide chemical
understanding to the deposition of high-quality, electronically coupled
MHP QD films that maintain both quantum confinement and their crystalline
phase and attain high photovoltaic performance.
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Acetic acidQD surface-bound acetateprocessing windowMHP QD filmsmethyl acetatemetal halide perovskiteacetic acidoptoelectronic propertiesHigh-Efficiency PhotovoltaicsSurface manipulationMHP QD surfacetreatment stepTargeted Ligand-Exchange ChemistryQD regimeenergy conversionHalide Perovskite Quantum DotsMHP QD surface chemistryfilm deposition processcouple MHP QDsMHP crystalligand-exchange proceduresspectroscopic techniquesmaterial formation energyoleate ligandschemical manipulationmolecular-level understandingQDSCbulk MHP filmquantum dotchemical understandingoleic acidsurface speciesquantum confinementphotovoltaic performancecorner-sharing structuremoisture aidsrecord-efficiency QDnanocrystalline size
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