scholarly journals In-situ ellipsometry measurements on the phase segregation of mixed halide lead perovskites

2021 ◽  
Author(s):  
Annik Bernhardt ◽  
Tharushi Ambagaspitiya ◽  
Martin Kordesch ◽  
Katherine Cimatu ◽  
Jixin Chen
Keyword(s):  
Phase Segregation ◽  
Green Laser ◽  
Bandgap Energy ◽  
Lead Iodide ◽  
Low Light ◽  
Nondestructive Technique ◽  
Methylammonium Lead Iodide ◽  
Conversion Efficiencies ◽  
Reversible Phase

Mixed halide lead perovskite such as methylammonium lead iodide bromides MAPb(BrxI1-x)3 have emerged as one of the most promising materials of future solar cells, offering high power conversion efficiencies and bandgap tunability. Among other factors, the reversible phase segregation under even low light intensities is still limiting their potential use. During this process, the material segregates locally into iodide-rich and bromide-rich phases, lowering the effective bandgap energy. While several studies have been done to illuminate the mechanism and suppression of phase segregation, fundamental aspects remain unclear. Phase compositions after segregation vary extensively between different studies and the exact amounts of phases often remain unmentioned. For iodide-rich phases, the end-point compositions at around x=0.2 are widely accepted but the proportion of the phase is difficult to measure. In this report, we observe the phase segregation using spectroscopic ellipsometry, a powerful, nondestructive technique that has been employed in the study of film degradation before. We obtained dynamic ellipsometric measurements from x=0.5 mixed halide lead perovskite thin films protected by a polystyrene layer under green laser light with a power density of ~11 W/cm2. Changes in the bandgap region can be correlated to the changes in composition caused by phase segregation, allowing for the kinetics to be observed. Time constants between 1.7(± 0.7)×10-3 s-1 for the segregation and 1.5(± 0.6)×10-4 s-1 for recovery were calculated. We expect ellipsometry to serve as a complementary technique to other spectroscopies in studying mixed-halide lead perovskites phase segregation in the future.

scholarly journals In situ investigation of degradation at organometal halide perovskite surfaces by X-ray photoelectron spectroscopy at realistic water vapour pressure

2017 ◽  
Vol 53 (37) ◽  
pp. 5231-5234 ◽  
Author(s):  
Jack Chun-Ren Ke ◽  
Alex S. Walton ◽  
David J. Lewis ◽  
Aleksander Tedstone ◽  
Paul O'Brien ◽  
...  
Keyword(s):  
Water Vapour ◽  
Photoelectron Spectroscopy ◽  
Ambient Pressure ◽  
Water Vapour Pressure ◽  
Lead Iodide ◽  
X Ray ◽  
In Situ Investigation ◽  
Organometal Halide Perovskite ◽  
Methylammonium Lead Iodide

Near-ambient-pressure X-ray photoelectron spectroscopy enables the study of the reaction of in situ-prepared methylammonium lead iodide (MAPI) perovskite at realistic water vapour pressures for the first time.

scholarly journals Direct calorimetric verification of thermodynamic instability of lead halide hybrid perovskites

2016 ◽  
Vol 113 (28) ◽  
pp. 7717-7721 ◽  
Author(s):  
G. P. Nagabhushana ◽  
Radha Shivaramaiah ◽  
Alexandra Navrotsky
Keyword(s):  
Formation Enthalpy ◽  
Ambient Air ◽  
Heat Of Formation ◽  
Lead Iodide ◽  
Methylammonium Lead Iodide ◽  
Conversion Efficiencies ◽  
Induced Defects ◽  
Thermodynamic Instability ◽  
Lead Halide

Hybrid perovskites, especially methylammonium lead iodide (MAPbI3), exhibit excellent solar power conversion efficiencies. However, their application is plagued by poor chemical and structural stability. Using direct calorimetric measurement of heats of formation, MAPbI3 is shown to be thermodynamically unstable with respect to decomposition to lead iodide and methylammonium iodide, even in the absence of ambient air or light or heat-induced defects, thus limiting its long-term use in devices. The formation enthalpy from binary halide components becomes less favorable in the order MAPbCl3, MAPbBr3, MAPbI3, with only the chloride having a negative heat of formation. Optimizing the geometric match of constituents as measured by the Goldschmidt tolerance factor provides a potentially quantifiable thermodynamic guide for seeking chemical substitutions to enhance stability.

scholarly journals Out-of-equilibrium processes in crystallization of organic-inorganic perovskites during spin coating

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Shambhavi Pratap ◽  
Finn Babbe ◽  
Nicola S. Barchi ◽  
Zhenghao Yuan ◽  
Tina Luong ◽  
...  
Keyword(s):  
Spin Coating ◽  
Grazing Incidence ◽  
Lead Iodide ◽  
In Situ Data ◽  
X Ray Scattering ◽  
Equilibrium Processes ◽  
Complex Phenomena ◽  
Methylammonium Lead Iodide ◽  
Solvent Complex

AbstractComplex phenomena are prevalent during the formation of materials, which affect their processing-structure-function relationships. Thin films of methylammonium lead iodide (CH3NH3PbI3, MAPI) are processed by spin coating, antisolvent drop, and annealing of colloidal precursors. The structure and properties of transient and stable phases formed during the process are reported, and the mechanistic insights of the underlying transitions are revealed by combining in situ data from grazing-incidence wide-angle X-ray scattering and photoluminescence spectroscopy. Here, we report the detailed insights on the embryonic stages of organic-inorganic perovskite formation. The physicochemical evolution during the conversion proceeds in four steps: i) An instant nucleation of polydisperse MAPI nanocrystals on antisolvent drop, ii) the instantaneous partial conversion of metastable nanocrystals into orthorhombic solvent-complex by cluster coalescence, iii) the thermal decomposition (dissolution) of the stable solvent-complex into plumboiodide fragments upon evaporation of solvent from the complex and iv) the formation (recrystallization) of cubic MAPI crystals in thin film.

In Situ Observation of Crystallization of Methylammonium Lead Iodide Perovskite from Microdroplets

Small ◽  
2017 ◽  
Vol 13 (26) ◽  
pp. 1604125 ◽  
Author(s):  
Yahui Li ◽  
Zhenhao Zhao ◽  
Feng Lin ◽  
Xiaobing Cao ◽  
Xian Cui ◽  
...  
Keyword(s):  
In Situ Observation ◽  
Lead Iodide ◽  
Methylammonium Lead Iodide

scholarly journals Polysilane-Inserted Methylammonium Lead Iodide Perovskite Solar Cells Doped with Formamidinium and Potassium

Energies ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4776
Author(s):  
Takeo Oku ◽  
Satsuki Kandori ◽  
Masaya Taguchi ◽  
Atsushi Suzuki ◽  
Masanobu Okita ◽  
...  
Keyword(s):  
Solar Cells ◽  
Perovskite Solar Cells ◽  
Hole Transport ◽  
Photovoltaic Devices ◽  
Lead Iodide ◽  
Temperature Range ◽  
Methylammonium Lead Iodide ◽  
Conversion Efficiencies ◽  
Perovskite Photovoltaic

Polysilane-inserted CH3NH3PbI3 perovskite photovoltaic devices combined with potassium and formamidinium iodides were fabricated and characterized. Decaphenylcyclopentasilane layers were inserted at the perovskite/hole transport interface and annealed across a temperature range of 180–220 °C. These polysilane-coated cells prevented PbI2 formation, and the conversion efficiencies were improved over extended periods of time.

scholarly journals Influence of metal halide perovskite modifications on structure and functionality

2021 ◽  
Author(s):  
◽  
Erin Service
Keyword(s):  
Metal Halide ◽  
Lead Iodide ◽  
Two Phase ◽  
Light Emitting ◽  
Thiocyanate Ion ◽  
Light Emitting Devices ◽  
Metal Halide Perovskite ◽  
Perovskite Crystal ◽  
Methylammonium Lead Iodide ◽  
Conversion Efficiencies

<p>Metal halide perovskites (ABX₃) represent an important class of materials with respect to optoelectronic applications such as photovoltaic and light-emitting devices. In this thesis, modification of these materials was explored through metal substitutions, halide substitutions and also nanocrystal synthesis. The ability for these modifications to take place was analyzed, and related to the effects on structural and optoelectronic properties.  Heterovalent metal substitutions were explored through the substitution of Bi³⁺ into methylammonium lead iodide (MAPbI₃). It was found that a two phase material composed of MAPbI₃ and MA₃Bi₂I₉ forms during these substitutions. This resulted in changes to electron-hole generation in the thin films and separation in photovoltaic devices, as observed through optical absorption and current-voltage measurements. Substitutions of Bi³⁺ and Tl⁺ were also carried out at dopant concentrations of 0.1–1%. Although the bulk crystal structure was maintained here, the power conversion efficiencies of devices decreased, with a bigger effect measured for Bi³⁺ doping. The ability for halide ions in MAPbBr₃ to be substituted with the thiocyanate ion (SCN)⁻ was investigated and compared to previous reports concerning MAPbI₃. From the studies conducted here, it is unlikely that the (SCN)⁻ ion becomes incorporated into the perovskite crystal lattice. This appeared to be primarily due to the reactivity of MA⁺ ion with (SCN)⁻. Finally, Cs₃Bi₂I₉ nanocrystals were synthesized via the hot injection method. This was supported through XRD, TEM and EDS measurements, where the crystals were found to display hexagonal symmetry. Subsequent experiments on the mixed halide nanocrystals (I/Br) revealed the sensitive nature of this synthesis to oxygen contamination.</p>

scholarly journals Influence of metal halide perovskite modifications on structure and functionality

2021 ◽  
Author(s):  
◽  
Erin Service
Keyword(s):  
Metal Halide ◽  
Lead Iodide ◽  
Two Phase ◽  
Light Emitting ◽  
Thiocyanate Ion ◽  
Light Emitting Devices ◽  
Metal Halide Perovskite ◽  
Perovskite Crystal ◽  
Methylammonium Lead Iodide ◽  
Conversion Efficiencies

<p>Metal halide perovskites (ABX₃) represent an important class of materials with respect to optoelectronic applications such as photovoltaic and light-emitting devices. In this thesis, modification of these materials was explored through metal substitutions, halide substitutions and also nanocrystal synthesis. The ability for these modifications to take place was analyzed, and related to the effects on structural and optoelectronic properties.  Heterovalent metal substitutions were explored through the substitution of Bi³⁺ into methylammonium lead iodide (MAPbI₃). It was found that a two phase material composed of MAPbI₃ and MA₃Bi₂I₉ forms during these substitutions. This resulted in changes to electron-hole generation in the thin films and separation in photovoltaic devices, as observed through optical absorption and current-voltage measurements. Substitutions of Bi³⁺ and Tl⁺ were also carried out at dopant concentrations of 0.1–1%. Although the bulk crystal structure was maintained here, the power conversion efficiencies of devices decreased, with a bigger effect measured for Bi³⁺ doping. The ability for halide ions in MAPbBr₃ to be substituted with the thiocyanate ion (SCN)⁻ was investigated and compared to previous reports concerning MAPbI₃. From the studies conducted here, it is unlikely that the (SCN)⁻ ion becomes incorporated into the perovskite crystal lattice. This appeared to be primarily due to the reactivity of MA⁺ ion with (SCN)⁻. Finally, Cs₃Bi₂I₉ nanocrystals were synthesized via the hot injection method. This was supported through XRD, TEM and EDS measurements, where the crystals were found to display hexagonal symmetry. Subsequent experiments on the mixed halide nanocrystals (I/Br) revealed the sensitive nature of this synthesis to oxygen contamination.</p>

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