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Short Photoluminescence Lifetimes in Vacuum-Deposited CH3NH3PbI3 Perovskite Thin Films as a Result of Fast Diffusion of Photogenerated Charge Carriers
journal contribution
posted on 2019-08-22, 12:04 authored by Vladimir S. Chirvony, Kairolla S. Sekerbayev, Daniel Pérez-del-Rey, Juan P. Martínez-Pastor, Francisco Palazon, Pablo P. Boix, Toktar I. Taurbayev, Michele Sessolo, Henk J. BolinkIt
is widely accepted that a long photoluminescence (PL) lifetime
in metal halide perovskite films is a crucial and favorable factor,
as it ensures a large charge diffusion length leading to a high power
conversion efficiency (PCE) in solar cells. It has been recently found
that vacuum-evaporated CH3NH3PbI3 (eMAPI) films show very short PL lifetimes of several nanoseconds.
The corresponding solar cells, however, have high photovoltage (>1.1
V) and PCEs (up to 20%). We rationalize this apparent contradiction
and show that eMAPI films are characterized by a very high diffusion
coefficient D, estimated from modeling the PL kinetics
to exceed 1 cm2/s. Such high D values
are favorable for long diffusion length as well as fast transport
of carriers to film surfaces, where they recombine nonradiatively
with surface recombination velocity S ∼ 104 cm/s. Possible physical origins leading to the high D values are also discussed.