Structural and optical properties of PbI<sub>2</sub>nanostructures obtained using the thermal evaporation method

We fabricate mixed halide perovskite films through dual-source vacuum deposition of PbX2 (X = Cl, Br, and I) and methyl ammonium iodide (MAI) precursors with various deposition ratios. Vacuum deposition is an optimal way for film fabrication because it gives a uniform perovskite film which is free from contamination such as metallic phase lead, residual solvent, and moisture. The ionization potential and bandgap of MAPb(I1-yBry)3 film are controlled by changing the halide composition and lattice constant. In contrast, MAPb(I1-yCly)3 film shows negligible difference from MAPbI3 in terms of structural and electronic properties, which is due to poor Cl incorporation in the film from the MACl removal during crystal formation. An excess supply of MAI is necessary to form a perovskite crystal structure. Based on the elemental stoichiometry analysis, the additional methyl ammonium cation with respect to Pb in the film plays a critical role in changing the electron affinity and energy level alignment.

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“…S1 (ESI †). 26,27 The PbI 2 peak decreases with increasing the MAI ratio, while the MAPbI 3 peak (*) becomes dominant in Fig. 1a.…”

Section: Resultsmentioning

confidence: 92%

Influence of halide precursor type and its composition on the electronic properties of vacuum deposited perovskite films

Kim

Seo

Kwon

et al. 2015

Phys. Chem. Chem. Phys.

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“…For PbI 2 , the morphology is comparable for all prepared films. The nanoflakes characteristic of evaporated lead iodide films are present independently of the substrate temperature and the HTL used (see the Supporting Information for SEM images of the full temperature series). In contrast to this, the morphology of the MAI films and the coverage are affected by the substrate temperature as presented using different HTLs in Figure , PTAA in c and for MeO-2PACz in d. With elevated temperature, the grains become smaller and change their shape from elongated to round.…”

Section: Resultsmentioning

confidence: 99%

Co-Evaporated p-i-n Perovskite Solar Cells beyond 20% Efficiency: Impact of Substrate Temperature and Hole-Transport Layer

Nazarov

Gil‐Escrig

Al‐Ashouri

et al. 2020

ACS Appl. Mater. Interfaces

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For methylammonium lead iodide perovskite solar cells prepared by co-evaporation, power conversion efficiencies of over 20% have been already demonstrated, however, so far only in n-i-p configuration. Currently, the overall major challenges are the complex evaporation characteristics of organic precursors that strongly depend on the underlying charge selective contacts and the insufficient reproducibility of the co-evaporation process. To ensure a reliable co-evaporation process, it is important to identify the impact of different parameters in order to develop a more detailed understanding. In this work, we study the influence of substrate temperature, underlying hole transporting material (polymer PTAA versus self-assembling monolayer molecule MeO-2PACz) and perovskite precursor ratio on the morphology, composition and performance of co-evaporated p-i-n perovskite solar cells. We first analyse the evaporation of pure precursor materials and show that the adhesion of methylammonium iodide (MAI) is significantly reduced with increased substrate temperature, while it remains almost unaffected for lead iodide (PbI2). This substrate temperature-dependent evaporation behaviour of MAI is also transferred to the co-evaporation process and can directly influence the perovskite composition. We demonstrate that the optimal substrate temperature window for perovskite deposition is close to room temperature. At high temperature not enough MAI for precise stoichiometry is incorporated even with very high MAI rates While at temperatures below -25 °C the conversion of MAI with PbI2 is inhibit and an amorphous yet unreacted film is formed. We observe that perovskite composition and morphology vary widely between the organic hole-transport layer (HTLs) PTAA and MeO-2PACz. For all substrate temperatures MeO-2PACz enables higher solar cell PCEs than PTAA. Through the combination of vapourdeposited perovskites and self-assembled monolayer, we achieve a stabilised power conversion efficiency of 20.6 %, which is the first reported PCE above 20% for evaporated perovskite solar cells in p-i-n architecture.

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“…A Gauss beam (r=1 μm) of 532 nm was used to excite the micro-plate from both the edge and center of the triangular micro-plate. The permittivity of the materials was calculated from the expression for the high-frequency refractive index [62].…”

Section: Simulationsmentioning

confidence: 99%

Edge Raman enhancement at layered PbI₂ platelets induced by laser waveguide effect

Ma¹,

Wu²,

Du³

et al. 2021

Nanotechnology

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As a two-dimensional (2D) layered semiconductor, lead iodide (PbI2) has been widely used in optoelectronics owing to its unique crystal structure and distinctive optical and electrical properties. A comprehensive understanding of its optical performance is essential for further application and progress. Here, we synthesized regularly shaped PbI2 platelets using the chemical vapor deposition method. Raman scattering spectroscopy of PbI2 platelets was predominantly enhanced when the laser radiated at the edge according to Raman mapping spectroscopy. Combining the outcome of polarized Raman scattering spectroscopy and finite-difference time domain simulation analysis, the Raman enhancement was proven to be the consequence of the enhancement effects inherent to the high refractive index contrast waveguide, which is naturally formed in well-defined PbI2 platelets. Because of the enlarged excited area determined by the increased propagation length of the laser in the PbI2 platelet formed waveguide, the total Raman enhancements are acquired rather than a localized point enhancement. Finally, the Raman enhancement factor is directly related to the thickness of the PbI2 platelet, which further confirms the waveguide-enhanced edge Raman. Our investigation of the optical properties of PbI2 platelets offers reference for potential 2D layered-related optoelectronic applications.

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Structural and optical properties of PbI₂nanostructures obtained using the thermal evaporation method

Cited by 9 publications

References 31 publications

Influence of halide precursor type and its composition on the electronic properties of vacuum deposited perovskite films

Influence of halide precursor type and its composition on the electronic properties of vacuum deposited perovskite films

Co-Evaporated p-i-n Perovskite Solar Cells beyond 20% Efficiency: Impact of Substrate Temperature and Hole-Transport Layer

Edge Raman enhancement at layered PbI₂ platelets induced by laser waveguide effect

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Structural and optical properties of PbI2nanostructures obtained using the thermal evaporation method

Cited by 9 publications

References 31 publications

Influence of halide precursor type and its composition on the electronic properties of vacuum deposited perovskite films

Influence of halide precursor type and its composition on the electronic properties of vacuum deposited perovskite films

Co-Evaporated p-i-n Perovskite Solar Cells beyond 20% Efficiency: Impact of Substrate Temperature and Hole-Transport Layer

Edge Raman enhancement at layered PbI2 platelets induced by laser waveguide effect

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Product

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Structural and optical properties of PbI₂nanostructures obtained using the thermal evaporation method

Edge Raman enhancement at layered PbI₂ platelets induced by laser waveguide effect