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Mechanism of Charge Transfer and Recombination Dynamics in Organo Metal Halide Perovskites and Organic Electrodes, PCBM, and Spiro-OMeTAD: Role of Dark Carriers
journal contribution
posted on 2015-12-30, 00:00 authored by Carlito S. Ponseca, Eline M. Hutter, Piotr Piatkowski, Boiko Cohen, Torbjörn Pascher, Abderrazzak Douhal, Arkady Yartsev, Villy Sundström, Tom J. SavenijeDespite the unprecedented interest
in organic–inorganic
metal halide perovskite solar cells, quantitative information on the
charge transfer dynamics into selective electrodes is still lacking.
In this paper, we report the time scales and mechanisms of electron
and hole injection and recombination dynamics at organic PCBM and
Spiro-OMeTAD electrode interfaces. On the one hand, hole transfer
is complete on the subpicosecond time scale in MAPbI3/Spiro-OMeTAD,
and its recombination rate is similar to that in neat MAPbI3. This was found to be due to a high concentration of dark charges,
i.e., holes brought about by unintentional p-type doping of MAPbI3. Hence, the total concentration of holes in the perovskite
is hardly affected by optical excitation, which manifested as similar
decay kinetics. On the other hand, the decay of the photoinduced conductivity
in MAPbI3/PCBM is on the time scale of hundreds of picoseconds
to several nanoseconds, due to electron injection into PCBM and electron–hole
recombination at the interface occurring at similar rates. These results
highlight the importance of understanding the role of dark carriers
in deconvoluting the complex photophysical processes in these materials.
Moreover, optimizing the preparation processes wherein undesired doping
is minimized could prompt the use of organic molecules as a more viable
electrode substitute for perovskite solar cell devices.