Mixed Cation Halide Perovskite under Environmental and Physical Stress

Abstract

Despite the ideal performance demonstrated by mixed perovskite materials when used as active layers in photovoltaic devices, the factor which still hampers their use in real life remains the poor stability of their physico-chemical and functional properties when submitted to prolonged permanence in atmosphere, exposure to light and/or to moderately high temperature. We used high resolution photoelectron spectroscopy to compare the chemical state of triple cation, double halide Csx(FA0.83MA0.17)(1−x)Pb(I0.83Br0.17)3 perovskite thin films being freshly deposited or kept for one month in the dark or in the light in environmental conditions. Important deviations from the nominal composition were found in the samples aged in the dark, which, however, did not show evident signs of oxidation and basically preserved their own electronic structures. Ageing in the light determined a dramatic material deterioration with heavily perturbed chemical composition also due to reactions of the perovskite components with surface contaminants, promoted by the exposure to visible radiation. We also investigated the implications that 2D MXene flakes, recently identified as effective perovskite additive to improve solar cell efficiency, might have on the labile resilience of the material to external agents. Our results exclude any deleterious MXene influence on the perovskite stability and, actually, might evidence a mild stabilizing effect for the fresh samples, which, if doped, exhibited a lower deviation from the expected stoichiometry with respect to the undoped sample. The evolution of the undoped perovskites under thermal stress was studied by heating the samples in UHV while monitoring in real time, simultaneously, the behaviour of four representative material elements. Moreover, we could reveal the occurrence of fast changes induced in the fresh material by the photon beam as well as the enhanced decomposition triggered by the concurrent X-ray irradiation and thermal heating.

Stabilizing Wide Bandgap Triple‐Halide Perovskite Alloy through Organic Gelators

“…[ 53–55 ] We characterize the changes in binding energy of the perovskite core‐level peaks in the presence and absence of MDBS additives; both films deposited showed nearly the same XPS peaks, indicating that the chemical components are the same at the surface level (see Figure S3, Supporting Information and the HR XPS spectra in Figure S4, Supporting Information). [ 56 ] These results support the premise that the perovskite structure is not disrupted by MDBS addition. However, while a weak decrement of the I3d‐ and Pb4f‐related signals intensity was observed in Cs22FABr15‐Cl3%‐MDBS0.1wt%, the signals related to C1 s , N1 s , O1 s , Cs3 d , and Br3 d show a general increment.…”

“…To quantify the components of C1 s signal in the unmodified perovskite, the carbon was classified into four different typologies: 1) the aliphatic C–C–(H) (285.0 eV); 2) alcoholic C–OH (286.6 eV) carbon components [ 57 ] attributed to the a‐specific contamination according to the presence of not expected oxygen. However, at this binding energy, the characteristic methylammonium carbon component [CH 3 ‐NH 3 ] + (C MA ) contribution cannot be excluded; [ 56,58 ] 3) the well‐resolved peak at 288.5 eV is attributed to formamidinium characteristic carbon component [HC‐(NH 2 ) 2 ] + (C FA ). [ 56 ] According to the last two attributions, a well‐resolved intense nitrogen peak component is observed at 400.8 eV, related to formamidinium nitrogen (N FA ), [ 54,58 ] typically associated with a weaker component at higher binding energy (401.7 eV).…”

“…However, at this binding energy, the characteristic methylammonium carbon component [CH 3 ‐NH 3 ] + (C MA ) contribution cannot be excluded; [ 56,58 ] 3) the well‐resolved peak at 288.5 eV is attributed to formamidinium characteristic carbon component [HC‐(NH 2 ) 2 ] + (C FA ). [ 56 ] According to the last two attributions, a well‐resolved intense nitrogen peak component is observed at 400.8 eV, related to formamidinium nitrogen (N FA ), [ 54,58 ] typically associated with a weaker component at higher binding energy (401.7 eV). This peak can be attributed to ammonium nitrogen (N MA ), even if lower than the expected 402.5 eV.…”

Ag/MgO Nanoparticles via Gas Aggregation Nanocluster Source for Perovskite Solar Cell Engineering

“…The deposition of Cs 0.05 (MA 0.17 FA 0.83 ) 95 Pb(I 0.83 Br 0.17 ) 3 was performed in nitrogen atmosphere following the antisolvent procedure, as detailed in our previous work [ 57 , 58 , 59 ]. A solution of PbI 2 , PbBr 2 , MABr, FAI and CsI in a solvent mixture of DMF and DMSO with a 4:1 ratio (v:v), respectively, was deposited by spin coating on top of the aforementioned substrates, following a sequential program at 1000 and 5000 rpm for 10 and 30 s, respectively.…”

A Brief Review of the Role of 2D Mxene Nanosheets toward Solar Cells Efficiency Improvement

“…In conclusion, we believe that our findings on Csx (FA 0.83 MA 0.17 ) (1x) Pb 3 (I 0.83 Br 0.17 ) show severe criticality in the stability of certain mixed perovskites that are comparable to single-halide materials. As a result, it appears that the effectiveness of agents based on electronic and chemical stabilisation of their functional properties, as well as the creative development of device architectures capable of interacting with disruptive agents, are critical for the long-term use of mixed perovskite [ 101 ].…”