Unraveling Reversible Quenching Processes of O₂, N₂, Ar, and H₂O in Metal Halide Perovskites at Moderate Photon Flux Densities

Abstract

However, to push the efficiency of this material class further, it is important to understand nonradiative recombination pathways upon photoexcitation under inert conditions as well as in the presence of atmospheric gases. Photoluminescence (PL) quantum efficiency, along with time resolved photoluminescence, provides easy-to-access key parameters that assess the quality of perovskite materials. Such techniques have been adopted by a vast number of groups to study the physical properties of MHP materials of different composition. [5][6][7] Yet, the effect that H 2 O, O 2 , and other gases have on the MHP PL has mostly been investigated under high power illumination with photon flux densities surpassing 10 20 photons s −1 m −2 , i.e., the equivalent of 100 suns and more. [5,6,8] Most of these studies focus on the degradation mechanisms of the material and the long-term stability of devices under diverse environmental conditions. However, the immediate and reversible PL quenching (PLQ) in MHP by different atmospheric molecules, at discrete pressure points and at low excitation densities of 1-10 suns, have not yet been looked at systematically. Given the fact that solar cells mostly operate at such moderate excitation density conditions, it is therefore obligatory to study the ongoing photophysical processes in more detail within this low excitation regime.In this report, we present a systematic study on the nature of second-order PLQ effects of O 2 , N 2 , Ar, and H 2 O on the so-called triple cation perovskite, or CsMAFA, containing cations of cesium, methylammonium (MA), and formamidinium (FA) as well as a mixture of bromide and iodide as anions. CsMAFA was chosen as a model material due to its superior film formation and stability, as opposed to the more common methylammonium lead triiodide (MAPbI 3 ). [9,10] We, however, note that all findings presented here also hold true in MAPbI 3 under low excitation densities. [11] By examining the PL emission and PL lifetimes, second-order quenching processes induced by the tested gas molecules, namely O 2 , N 2 , and Ar, as well as for H 2 O, are investigated quantitatively. The Stern-Volmer (SV) analysis is then applied to PL emission and lifetime measurements at different partial pressures for each gas to identify the nature of the quenching process and the underlaying diffusion kinetics. Metal halide perovskites (MHP), as used in photovoltaic (PV) applications,show a rich photophysics in inert and ambient atmosphere. The presence of atmospheric molecules leads to processes that enhance as well as reduce their photoluminescence (PL) emission. Various phenomena are previously described for a wide variety of gas molecules and different classes of MHP, with a particular interest on the long-term stability for PV applications. However, reversible PL quenching (PLQ) processes, which may be regarded equally important for the performance of PV and other optoelectronic applications, are neglected in other studies. This holds true for O 2 and H 2 O, but especially for low-reacti...

Mechanism and Timescales of Reversible p‐Doping of Methylammonium Lead Triiodide by Oxygen

“…Furthermore, for surface‐specific doping much faster timescales were to be expected, particularly for oxygen/air exposure (at the oxygen partial pressure used in our experiments, it takes ≈5 ns for every surface site to be hit by an oxygen molecule [ 47 ] ). This is further supported by the few 10 s timescale observed for changing the photoluminescence yield of oxygen‐exposed MAPbBr 3 [ 48 ] and a triple‐cation perovskite, [ 49 ] where surface interactions dominate.…”

In Situ Vapor‐Phase Halide Exchange of Patterned Perovskite Thin Films

“…along the GBs. [35] However, once the phase transformation is completed (t MABr = 40 min), we observe that the photocurrent recovers after the saturation of impurity adsorption during the 473 nm pulsed illumination, presumably due to the presence of an excess amount of MABr ( Figure S10, Supporting Information) that fills the GBs. Pulsed illumination with the 520 nm laser on this sample exhibits a fluctuation in the ON current, which is ascribed to the excitation with a near-band gap (2.38 eV) coupled with the shallow traps induced by oxygen adsorption.…”

Environment‐Dependent Metastable Nonradiative Recombination Centers in Perovskites Revealed by Photoluminescence Blinking

“…Note that the reported atmosphere-dependent photophysical properties of perovskites are often different depending on the sample (bulk single crystals, polycrystalline thin films, micro-/ nanocrystals). [7][8][9]11,17,18,33,34] Usually, PL experiments are conducted under N 2 atmosphere, and no significant PL quenching is found. We observed the same for 77% of the studied individual crystals where immersion in N 2 did not lead to any changes of PL behavior.…”