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Role of Water in Suppressing Recombination Pathways in CH3NH3PbI3 Perovskite Solar Cells
journal contribution
posted on 2019-06-10, 00:00 authored by Ankur Solanki, Swee Sien Lim, Subodh Mhaisalkar, Tze Chien SumMoisture
degradation of halide perovskites is the Achilles heel
of perovskite solar cells. A surprising revelation in 2014 about the
beneficial effects of controlled humidity in enhancing device efficiencies
overthrew established paradigms on perovskite solar cell fabrication.
Despite the extensive studies on water additives in perovskite solar
cell processing that followed, detailed understanding of the role
of water from the photophysical perspective remains lacking; specifically,
the interplay between the induced morphological effects and the intrinsic
recombination pathways. Through ultrafast optical spectroscopy, we
show that both the monomolecular and bimolecular recombination rate
constants decrease by approximately 1 order with the addition of an
optimal 1% H2O by volume in CH3NH3PbI3 as compared to the reference (without the H2O additive). Correspondingly, the trap density reduces from 4.8 ×
1017 cm–3 (reference) to 3.2 × 1017 cm–3 with 1% H2O. We obtained
an efficiency of 12.3% for the champion inverted CH3NH3PbI3 perovskite solar cell (1% H2O additive)
as compared to the 10% efficiency for the reference cell. Increasing
the H2O content further is deleterious for the device.
Trace amounts of H2O afford the benefits of surface trap
passivation and suppression of trap-mediated recombination, whereas
higher concentrations result in a preferential dissolution of methylammonium
iodide during fabrication that increases the trap density (MA vacancies).
Importantly, our study reveals the effects of trace H2O
additives on the photophysical properties of CH3NH3PbI3 films.
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trace H 2 O additivesH 2 O contentSuppressing Recombination Pathwaysdevice efficiencies overthrewtrap densityreferencephotophysicalefficiencyCH 3 NH 3 PbI 3 filmsrecombination rate constants decreaseMAcmCH 3 NH 3 PbI 3 Perovskite Solar Cells Moisture degradationCH 3 NH 3 PbI 3 perovskiteH 2 OH 2 O additivesurface trap passivationCH 3 NH 3 PbI 3fabrication