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Why are Hot Holes Easier to Extract than Hot Electrons from Methylammonium Lead Iodide Perovskite?
Author(s) -
Dursun Ibrahim,
Maity Partha,
Yin Jun,
Turedi Bekir,
Zhumekenov Ayan A.,
Lee Kwang Jae,
Mohammed Omar F.,
Bakr Osman M.
Publication year - 2019
Publication title -
advanced energy materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 10.08
H-Index - 220
eISSN - 1614-6840
pISSN - 1614-6832
DOI - 10.1002/aenm.201900084
Subject(s) - materials science , perovskite (structure) , thermalisation , band gap , delocalized electron , charge carrier , optoelectronics , density functional theory , chemical physics , perovskite solar cell , solar cell , excitation , computational chemistry , chemistry , atomic physics , crystallography , physics , engineering , organic chemistry , electrical engineering
Charge‐carriers photoexcited above a semiconductor's bandgap rapidly thermalize to the band‐edge. The cooling of these difficult to collect “hot” carriers caps the available photon energy that solar cells–including efficient perovskite solar cells–may utilize. Here, the dynamics and efficiency of hot carrier extraction from MAPbI 3 (MA = methylammonium) perovskite by spiro‐OMeTAD (a hole‐transporting layer) and TiO 2 (an electron‐transporting layer) are investigated and explained using both ultrafast electronic spectroscopy and theoretical modeling. Time‐resolved spectroscopy reveals a quasi‐equilibrium distribution of hot carriers forming upon excess‐energy excitation of the perovskite–a distribution largely unaffected by the presence of TiO 2 . In contrast, the quasi‐equilibrium distribution of hot carriers is virtually nonexistent when spiro‐OMeTAD is present, which is indicative of efficient hot hole extraction at the interface of MAPbI 3 . Density functional theory calculations predict that deep energy‐levels of MAPbI 3 exhibit electronically delocalized character, with significant overlap with the localized valence band charge of the spiro‐OMeTAD molecules lying on the surface of MAPbI 3 . Consequently, hot holes are easily extracted from the deep energy‐levels of MAPbI 3 by spiro‐OMeTAD. These findings uncover the origins of efficient hot hole extraction in perovskites and offer a practical blueprint for optimizing solar cell interlayers to enable hot carrier utilization.