Mechanistic insights into perovskite photoluminescence enhancement: light curing with oxygen can boost yield thousandfold

Abstract

A light-induced photoluminescence (PL) enhancement in surface-deposited methylammonium lead iodide (CH3NH3PbI3) perovskites was investigated in detail using time-resolved luminescence microscopy. We found the PL intensity to increase up to three orders of magnitude upon light illumination with an excitation power density of 0.01-1 W cm(-2). The PL enhancement is accompanied by an increase of the PL lifetime from several nanoseconds to several hundred nanoseconds and also by an increase of the initial amplitude of the PL decay. The latter suggests excited state quenching at the subpicosecond timescale. We propose a model where the trapping sites responsible for non-radiative charge recombination can be de-activated by a photochemical reaction involving oxygen. The reaction zone is spatially limited by the excitation light-penetration depth and diffusion length of the charge carriers. The latter increases in the course of the light-curing process making the reaction zone spreading from the surface towards the interior of the crystal. The PL enhancement can be reversed by switching on/off the excitation light or switching the atmosphere between oxygen and nitrogen. Slow diffusion of the reactants and products and equilibrium between the active and "cured" trapping sites are proposed to be the reasons for peculiar responses of PL to such varied experimental conditions.

Strong Quantum Confinement and Fast Photoemission Activation in CH3NH3PbI3 Perovskite Nanocrystals Grown within Periodically Mesostructured Films

“…This is in contrast with the slow photoactivation of the PL presented by a bulk film of similar thickness (i.e., 200 nm). Such slow dynamics of the PL of bulk MAPbI 3 has been previously observed in the past, [29,30] and has been proposed to originate at trap-filling caused by the photoinduced migration of ions within the perovskite lattice under illumination. [31] Within this picture it is reasonable to assume that the time needed for ions to traverse the size of the nanocrystal should be orders of magnitude smaller than that for the bulk case.…”

Gas-solid reaction based over one-micrometer thick stable perovskite films for efficient solar cells and modules

“…TRPL was acquired using the time-correlated, single-photon counting technique (Hamamatsu, C10627), and excitation was provided by a femtosecond mode-locked Ti:sapphire laser (Spectra-Physics, MAITAI XF-IMW) at 450 nm with an average power at 8 MHz of 0.74 mW. In TRPL, perovskite films were covered with PMMA on the top of the perovskite layer to exclude/minimize the influence of ambient air (especially the influence from H 2 O and O 2 ) 67–70 . SIMS (Kratos Axis ULTRA) equipped with quadrupole mass spectrometer (HAL 7, Hiden Analytical) was used to collect the elemental signal in positive ion detection mode (PID).…”

Enhanced Organo-Metal Halide Perovskite Photoluminescence from Nanosized Defect-Free Crystallites and Emitting Sites

“…4c), and very similar to that of intentionally photo-cured large perovskite crystals. 30 This finding can be understood as a result of the fast and efficient trap passivation of the small crystals, with the dissolved bulk oxygen as the reactant.…”

“…1,15,19,[25][26][27][28][29] As we will show, 4 light-irradiation at ambient conditions removes, or de-activates, the traps leading to the observed increase of PL. Recent studies of the PL enhancement effect in different atmospheres 11,13 and our own experiments 30 showed that this occurs through a photochemical reaction involving oxygen.…”

“…The PL decay kinetics on the nanosecond time scale is a good marker of this process. 30 At the earliest times after onset of illumination the decay is very short (few ns), at intermediate times (~1 min) it is highly multiexponential with both very short and very long (several hundred ns) life times, reflecting highly quenched and non-quenched PL, respectively. 30 We also studied the atmosphere dependence of the PL enhancement of small (~100 nm) crystals produced by scratching of the perovskite film.…”