A Theoretical Framework for Microscopic Surface and Interface Dipoles, Work Functions, and Valence Band Alignments in 2D and 3D Halide Perovskite Heterostructures

Traoré, Boubacar; Basera, Pooja; Ramadan, Alexandra J.; Snaith, Henry J.; Katan, Claudine; Even, Jacky

doi:10.1021/acsenergylett.1c02459

Cited by 23 publications

(37 citation statements)

References 57 publications

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“…In all cases, PbI 2 -termination presents a deeper absolute valence energy level as compared to CsI-termination for these unrelaxed slab surfaces. This can be explained by the larger surface dipoles present at the PbI 2 -terminated surface, which we have thoroughly discussed in this work 123 . DFT-1/2 predicts E abs v values that are closer to those predicted at the G0W 0@HSE(50%) level.…”

Section: Assessing Ionization Energies or Absolute Valence Energy Lev...mentioning

confidence: 80%

Band gap, effective masses, and energy level alignment of 2D and 3D halide perovskites and heterostructures using DFT-1/2

Traoré

Even

Pédesseau

et al. 2022

Phys. Rev. Materials

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We revisit the Slater half-occupation technique within the DFT-1/2 method to provide improved accuracy of 2D and 3D halide perovskites band gaps at a moderate computational cost. We propose an electron removal scheme from the halide states that drastically improve the predicted band gaps of 2D compounds. Concurrently, we compute the effective masses of the considered structures and show that DFT-1/2 describes them with a nice degree of accuracy when compared to available experimental data. Moreover, we assess the suitability of DFT-1/2 to compute the energy level alignments of this family of compounds. We compare the results in light of those we predict using the hybrid functional HSE06 and the many body perturbation theory within the G0W 0 approximation. We discuss the limitations of our refined DFT-1/2 scheme, which tends to overestimate the downshift of the absolute valence energy levels of the layered perovskite systems.We anticipate that our results would be useful to initiate benchmark studies and investigate large systems such as heterostructures for which other approaches may be out of reach.

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Section: Assessing Ionization Energies or Absolute Valence Energy Lev...mentioning

confidence: 80%

Band gap, effective masses, and energy level alignment of 2D and 3D halide perovskites and heterostructures using DFT-1/2

Traoré

Even

Pédesseau

et al. 2022

Phys. Rev. Materials

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“…In contrast, the red and blue regions were more clearly distributed for the TFPTMS molecule, indicating that the strong electron‐withdrawing effect of fluorinated alkyl chains resulted in isolated electron cloud overlap (−18.25 eV for trifluoropropyl group and −23.62 eV for the methoxy group), namely increased dipole moment (2.080). [ 36 ] The change of electron cloud distribution led to an enlarged dielectric constant for the organic ligands, thus diminishing the dielectric confinement in quasi‐2D perovskite. The rising temperature and weakened dielectric confinement synergically result in more serious exciton dissociation for the TFPTMS‐based perovskite film.…”

Section: Resultsmentioning

confidence: 99%

Self‐Healing Perovskite Films Enabled by Fluorinated Cross‐Linked Network Targeting Flexible Light‐Emitting Diode

Zang

Cai

Zou

et al. 2022

Advanced Optical Materials

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Perovskite light‐emitting diodes (PeLEDs) are promising technologies for advanced display and lighting source applications. Alongside tremendous efforts to improve efficiency, developing flexible devices could potentially enable PeLEDs compatible with wearable, foldable, bio‐integrated, and other intriguing functionalities. However, the flexible PeLEDs currently have not received enough attention. The overall performance still lags behind the rigid one, mainly attributed to the lack of mechanically stable perovskite thin films with desirable optical and electrical properties. Herein, a self‐healing strategy to achieve flexible perovskite films with improved mechanical reliability and optoelectrical properties is proposed. A multi‐functional silane molecule of (3,3,3‐trifluoropropyl) trimethoxysilane (TFPTMS) is incorporated into a perovskite precursor, which could undergo an in situ cross‐linking process and generate a flexible Si–O–Si network within the perovskite films. In addition, the reversible hydrolysis and condensation reactions and the fluorinated alkyl chains endow the perovskite films with self‐healing capability. Accordingly, the synergistic influences contribute to high‐efficiency flexible PeLEDs with an external quantum efficiency (EQE) of 16.2%. Moreover, 75% of the initial efficiency value is reserved even after 1000 bending cycles. This work paves a way to rationalize flexible perovskite thin films for various optoelectronic applications.

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“…[41] The surface dipole will influence the work function, energy level alignments and interfacial charge transport. [41,42] Therefore, the permanent dipole moments of o/m/p-MeO were calculated and are shown in Figure 3a-c. o/m-MeO (3.72/3.42 Debye) have larger dipoles than p-MeO (1.19 Debye), which is beneficial to band alignment and charge transport at the interface.…”

Section: Molecular Polaritymentioning

confidence: 99%

Machine‐Learning Modeling for Ultra‐Stable High‐Efficiency Perovskite Solar Cells

Zhang

et al. 2022

Advanced Energy Materials

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low-carbon and renewable clean energy due to its high carrier mobility, wide absorbance, low exciton energy, long carrier lifetime and diffusion length, high defect tolerance and low-cost preparation. [9,10] Researchers have made considerable effort to improve the power conversion efficiency (PCE) and longterm stability of PSCs. In 2009, MAPbBr 3 (MA = methylamine, CH 3 NH 2 ) was used as a new dye in a dye-sensitized solar cell. [3] Later, all-solid-state perovskite solar cells were prepared in 2012. [11,12] During the first stage, researchers attempted to improve the preparation technology for the solid perovskite absorber. The anti-solvent method, gas pumping, blade coating, vacuum deposition, magnetron sputtering, and other methods have been developed to eliminate macro defects such as pin holes and prepare dense thin films of perovskites. [13] Micro-defects, such as point defects in the bulk, grain boundaries, dangling bonds on the film surface and interfacial stress from thermal mismatch, have also been reduced by additive engineering, solvent engineering, composite engineering and strain engineering. [14] After great effort, the efficiency and long-term stability of PSCs have been improved considerably. However, the mechanisms of how efficiency and stability are affected by bandgap, trap density, grain boundaries, carrier lifetime and film roughness remain unknown due to too many involved parameters.Understanding the key factor driving the efficiency and stability of semiconductor devices is vital. To date, the key factor influencing the long-term stability of perovskite solar cells (PSCs) remains unknown because of the many influencing factors. In this work, through machine learning, the influences of five factors, including grain size, defect density, bandgap, fluorescence lifetime, and surface roughness, on the efficiency and stability of PSCs have been revealed. It is found that the bandgap has the greatest influence on the efficiency, and the surface roughness and grain size are most influential to the long-term stability. A mathematical model is given to predict efficiency based on fluorescence lifetime and bandgap. Guided by the model, four groups of experiments are conducted to confirm the machine-learning predictions and a PSC with 23.4% efficiency and excellent long-term stability is obtained, as manifested by retention of 97.6% of the initial efficiency after 3288 h aging in the ambient environment, the best stability under these conditions. This work shows that machine learning is an effective means to enrich semiconductor physical models.

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A Theoretical Framework for Microscopic Surface and Interface Dipoles, Work Functions, and Valence Band Alignments in 2D and 3D Halide Perovskite Heterostructures

Cited by 23 publications

References 57 publications

Band gap, effective masses, and energy level alignment of 2D and 3D halide perovskites and heterostructures using DFT-1/2

Band gap, effective masses, and energy level alignment of 2D and 3D halide perovskites and heterostructures using DFT-1/2

Self‐Healing Perovskite Films Enabled by Fluorinated Cross‐Linked Network Targeting Flexible Light‐Emitting Diode

Machine‐Learning Modeling for Ultra‐Stable High‐Efficiency Perovskite Solar Cells

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