![a) The three types of position of PbI2 vacancy in MAPbI3. Adapted with permission.[⁴⁴] Copyright 2014, American Chemical Society. b) Spatial and energy mapping of the densities of trap states in the single crystal and c) MAPbI3 film. Adapted with permission.[⁴⁷] Copyright 2020, The American Association for the Advancement of Science.](https://www.researchgate.net/publication/380530025/figure/fig1/AS:11431281242508179@1715536119353/a-The-three-types-of-position-of-PbI2-vacancy-in-MAPbI3-Adapted-with-permission_Q320.jpg)
![a) The statistical data of the size and number of MAPbI3 single crystals in their precursor solutions under light and b) dark conditions, respectively, the light intensity of which is 64 mW cm⁻². The insert images are the MAPbI3 single crystal grown from its precursor solution after 36 h. Adapted with permission.[⁵⁸] Copyright 2022, The Royal Society of Chemistry. c) MAPbI3 films obtained by spin‐coating under different illumination intensities 0 mW cm⁻², d) 52 mW cm⁻²), and the statistics of the grain diameter distribution of the MAPbI3 microcrystalline in films. Adapted with permission.[⁵⁸] Copyright 2022, The Royal Society of Chemistry.](https://www.researchgate.net/publication/380530025/figure/fig2/AS:11431281242533320@1715536119806/a-The-statistical-data-of-the-size-and-number-of-MAPbI3-single-crystals-in-their_Q320.jpg)
![a) Before light soaking, and after exposing the entire film to simulated sunlight (AM 1.5, 100 mW cm⁻²) for 60 min and leaving in the dark for 21 and 234 min (all images have the same PL intensity scale normalized to the average PL intensity in (a), scale bars, 1 mm).[⁵⁹] Copyright 2016, Springer Nature. b) The J–V curves of the different grain size champion photovoltaic cells under 100 mW cm⁻² of solar light AM 1.5G, 60 represents 60° annealing. Adapted with permission.[⁶⁰] Copyright 2021, American Chemical Society. c) Average overall PCE (left) and JSC (right) as a function of crystalline grain size. Adapted with permission.[⁶¹] Copyright 2015, The American Association for the Advancement of Science.](https://www.researchgate.net/publication/380530025/figure/fig3/AS:11431281242508180@1715536120380/a-Before-light-soaking-and-after-exposing-the-entire-film-to-simulated-sunlight-AM_Q320.jpg)
![Normalized PL emission spectra of different grain size a) 16.2 nm, b) 28.7 nm, c) 43.5 nm, d) 57.8 nm, e) 81.1 nm, f) 105.7 nm, g) 157.5, and h) 135.2 nm under light irradiation (10 mW cm⁻²). Adapted with permission.[⁶⁰] Copyright 2021, American Chemical Society.](https://www.researchgate.net/publication/380530025/figure/fig4/AS:11431281242533321@1715536120701/Normalized-PL-emission-spectra-of-different-grain-size-a-162nm-b-287nm-c-435nm_Q320.jpg)
![a) Diagram of different situations in which the lattice size changes when light and heat act alone. Adapted with permission.[⁶⁵] Copyright 2021, American Chemical Society. b,c) Schematic describing the crystal structure change before illumination (local distortion) and after illumination (lattice expansion). Adapted with permission.[⁵⁵] Copyright 2018, The American Association for the Advancement of Science. d) First‐order derivative of the J–V curves before and after 2 h of light soaking. Adapted with permission.[⁵⁵] Copyright 2018, The American Association for the Advancement of Science. e) Lattice constant as a function of illumination time. Error bars indicate the error from peak fitting. Adapted with permission.[⁵⁵] Copyright 2018, The American Association for the Advancement of Science. f) Mechanism for the giant photostriction in MAPbI3. Schematic illustrations (not to scale) show that the weakening of the hydrogen bonding between the amine group and the iodine ion by photo‐generated carriers leads to the lattice expansion. Adapted with permission.[⁶⁷] Copyright 2016, Springer Nature.](https://www.researchgate.net/publication/380530025/figure/fig5/AS:11431281242533322@1715536121001/a-Diagram-of-different-situations-in-which-the-lattice-size-changes-when-light-and-heat_Q320.jpg)
May 2024
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2 Citations
Metal halide perovskites (MHPs) have excellent characteristics and present great potential in a broad range of applications such as solar cells, light‐emitting diodes, and photodetectors. However, the light stability of devices remains an unresolved issue and has received great research attention. Under light illumination, MHPs exhibit various anomalous phenomena, such as photoluminescence (PL) enhancement, defect curing, PL blinking, and phase segregation. These phenomena are commonly considered intimately correlated with the performance and stability of MHP devices. In recent years, significant efforts have been made experimentally and theoretically toward understanding the physical origins of these anomalous effects. However, most research focuses on negative effects while the positive effects are mostly ignored. Herein, the positive effects and the negative effects of light soaking in MHPs are systematically discussed with a classification of the correlated physical mechanisms by specifically focusing on variation occurring in timescale from second to hour, corresponding to the unique ionic–electronic interaction. This intends to provide a new insight into ion effects on excellent properties of perovskites, and deep physical understanding of charge‐carrier and ion dynamics in perovskite, and theoretical guidelines for the fabrication of high‐quality and stability perovskite‐based photovoltaic and photoelectric devices.
![a) The crystal structure of MHPs family. b) XRD patterns of pristine MAPbI3 and hydrated MAPbI3. Reproduced with permission.[⁶⁶] Copyright 2015, American Chemical Society. c) (Top) XRD patterns of the FA1−xCsxPbI3 films. (below) XRD patterns with magnified (101) peak of FA1−xCsxPbI3 films. Reproduced with permission.[⁶⁸] Copyright 2015, Wiley‐VCH GmbH. d) The light stability test of (top) (FAPbI3)0.9(MAPbBr3)0.1 without Cs⁺ alloying and (below) Cs‐containing (FAPbI3)0.9(MAPbBr3)0.05(CsPbBr3)0.05. Reproduced with permission.[⁷⁹] Copyright 2019, American Chemical Society. e) Grazing incidence X‐ray diffraction patterns of (top) MAPbIxCl3‐x (below) MAPb0.90In0.10I3Cl0.10 perovskite films. Reproduced with permission.[⁵⁸] Copyright 2016, Wiley‐VCH GmbH. f) Schematic diagram showing a possible reaction that occurs when four types of Pb²⁺, Zn²⁺, Mg²⁺, and Cd²⁺ are alloyed in the B‐site. Reproduced with permission.[⁸⁵] g) Synchrotron X‐ray scattering analysis of alloy perovskites, magnified (100) plane peaks of bare MAPbBr3 and alloy MA(PbMgZnCd)Br3, MA(PbMgZn)Br3, MA(PbMgCd)Br3, MA(PbCd)Br3, MA(PbZn)Br3, and MA(PbMg)Br3. Reproduced with permission.[⁸⁵] Copyright 2022, American Chemical Society. h) The 3D cubic crystallographic structure and 1D hexagonal crystallographic structure of alloy CsPb1−xCdxBr3 obtained by changing Cd contents. Reproduced with permission.[⁵⁹] Copyright 2020, Wiley‐VCH GmbH.](https://www.researchgate.net/publication/366590218/figure/fig1/AS:11431281179444596@1691191367961/a-The-crystal-structure-of-MHPs-family-b-XRD-patterns-of-pristine-MAPbI3-and-hydrated_Q320.jpg)
![SEM images of the a) FAPbI3(Cl) and b) FA0.9Cs0.1PbI3(Cl) films. Reproduced with permission.[¹⁰⁹] Copyright 2017, Wiley‐VCH GmbH. c) TEM image of CsPbBr3. d) The TEM images of alloy CsPb1−xCdxBr3 with values of 0.1, e) 0.56 and f), g) 0.92. Reproduced with permission.[⁵⁹] Copyright 2020, Wiley‐VCH GmbH.](https://www.researchgate.net/publication/366590218/figure/fig2/AS:11431281179463904@1691191372332/SEM-images-of-the-a-FAPbI3Cl-and-b-FA09Cs01PbI3Cl-films-Reproduced-with_Q320.jpg)
![a) The molecular orbital of PbI2 in the 3D MHPs. Reproduced with permission.[¹¹¹] b) The schematic illustration of the valence band and conduction band of 3D MHPs. Reproduced with permission.[¹¹¹] Copyright 2020, American Chemical Society. c) Schematic energy‐level diagram of the MASn1−xPbxI3 solid solution perovskites. Reproduced with permission.[³⁷] Copyright 2014, American Chemical Society. d) Energy band picture of FA0.75MA0.25Sn1−xGexI3 with different content of Ge. Reproduced with permission.[⁵⁴] e) The UV‐vis absorption of FA0.75MA0.25Sn1−xGexI3 with different content of Ge. Reproduced with permission.[⁵⁴] Copyright 2018, American Chemical Society. f) The absorption spectra of FAxMA1−xPbI3 films (x = 0, 10%, 20%, 30%). Reproduced with permission.[⁶⁵] Copyright 2017, American Chemical Society. g) PL spectra and h) absorption spectra of FA(1−x)CsxPbBr3 (x = 0‐0.6). Reproduced with permission.[¹²¹] Copyright 2017, Wiley‐VCH GmbH. i) PL quantum efficiency spectra of the MAPbI3 and Cs0.05FA0.79MA0.16Pb(I0.8Br0.2)3 perovskite films. Reproduced with permission.[¹⁰⁸] Copyright 2019, Wiley‐VCH GmbH.](https://www.researchgate.net/publication/366590218/figure/fig3/AS:11431281179410925@1691191376485/a-The-molecular-orbital-of-PbI2-in-the-3D-MHPs-Reproduced-with-permission-b-The_Q320.jpg)
![a) The crystal structure of (C4H9NH3)2(CH3NH3)2PbBr10 at below Curie point and perovskite framework at below Curie point. Reproduced with permission.[¹³¹] b) Polarization versus electric field hysteresis loops of (C4H9NH3)2(CH3NH3)2PbBr10. Reproduced with permission.[¹³¹] Copyright 2017, Wiley‐VCH GmbH. c) The (trimethylammonium)3Sb2Cl9 with ferroelectric transform to (trimethylammonium)4‐FeCl4‐Sb2Cl9 with ferroelastic by inserting inorganic layers FeCl4. Reproduced with permission.[¹³⁴] Copyright 2022, Springer Nature.](https://www.researchgate.net/publication/366590218/figure/fig4/AS:11431281179350924@1691191380721/a-The-crystal-structure-of-C4H9NH32CH3NH32PbBr10-at-below-Curie-point-and-perovskite_Q320.jpg)
![a) The atomic structure of MAPbI3 showing superoxide ion O²⁻ occupying an iodide vacancy. Reproduced with permission.[²⁹] Copyright 2017, Springer Nature. b) The time‐resolved photoliminescence spectra for ITO/SnO2/FAPbI3(Cl) and FA0.9Cs0.1PbI3(Cl) perovskite film. Reproduced with permission.[¹⁰⁹] c) The I–V curves of ITO/SnO2/FAPbI3(Cl) and FA0.9Cs0.1PbI3(Cl) perovskite film/MoO3/Ag and the value of dilm trap density. Reproduced with permission.[¹⁰⁹] Copyright 2017, Wiley‐VCH GmbH. d) Defect spectroscopy of solar cell with the different active perovskite layer of FA0.83MA0.17Pb(I0.83Br0.17)3, Cs‐alloyed, Rb‐alloyed and Cs, Rb‐alloyed with FA0.83MA0.17Pb(I0.83Br0.17)3 by thermally stimulated current measurement. Reproduced with permission.[¹⁴⁴] Copyright 2018, Wiley‐VCH GmbH. e) Calculation supercell structure and formation energy of vacancy of of FAPbI3 and alloy perovskite. Reproduced with permission.[⁸⁴] Copyright 2018, Springer Nature. f) The time‐resolved photoliminescence spectra of pure Pb and Sn perovskite and different concentrations alloy Sn–Pb perovskites. Reproduced with permission.[⁸²] Copyright 2018, Wiley‐VCH GmbH.](https://www.researchgate.net/publication/366590218/figure/fig5/AS:11431281179444613@1691191384911/a-The-atomic-structure-of-MAPbI3-showing-superoxide-ion-O-occupying-an-iodide-vacancy_Q320.jpg)
