Unveiling the Valence State of Interstitial Bromine on Charge Carrier Lifetime in CH₃NH₃PbBr₃ by Quantum Dynamics Simulation

Interstitial halogens are detrimental to the optoelectronic properties of metal halide perovskites. Using nonadiabatic (NA) molecular dynamics, we demonstrate that the valence state of interstitial bromine strongly changes the carrier lifetimes of MAPbBr3 (MA = CH3NH3+). Both neutral and negatively charged interstitial bromine create no midgap states, and they decrease the bandgap, weaken the NA coupling, and accelerate decoherence in a different extent with respect to pristine MAPbBr3, making free charge recombination either slow down about a 3-fold or remain largely unchanged. In contrast, a positively charged interstitial bromine forms a Br trimer and introduces a deep electron trap state, causing a 1.4-fold increase of charge recombination followed by a rapid electron trapping or across the bandgap because of an enhanced NA coupling. The simulations uncover the influence of different charged interstitial bromine defects on MAPbBr3 carrier lifetimes and provide rational guidelines for optimizing perovskite solar cells

Extending Carrier Lifetime of Antiferromagnetic LaFeO₃ Perovskite by Regulating Magnetic Ordering: Time-Domain Ab Initio Analysis

Focusing on LaFeO3, we investigated the effects of magnetic ordering on carrier relaxation using time-domain density functional theory and nonadiabatic molecular dynamics. The results show that the hot energy and carrier relaxation occur on a sub-2 ps time scale due to the strong intraband nonadiabatic coupling, and the corresponding time scales are distinct depending on the magnetic ordering of LaFeO3. Importantly, the energy relaxation is slower than hot carrier relaxation, guaranteeing photogenerated hot carriers can be effectively relaxed to the band edge before cooling. Following hot carrier relaxation, the charge recombination occurs on the nanosecond scale due to the small interband nonadiabatic coupling and short pure-dephasing times. In addition, the A-AFM system has the longest carrier lifetimes because of its weakest nonadiabatic coupling. Our study suggests that the carrier lifetime can be controlled by changing the magnetic ordering of perovskite oxides and provides valuable principles for the design of high-performance photoelectrodes

Strong Influence of the Anion Radius on the Passivation of Selenium Vacancy in Monolayer InSe: Insights from Time-Domain Ab Initio Analysis

Using nonadiabatic molecular dynamics combined with the time-domain density functional theory, we have explored the influence of selenide vacancy and passivation of anions with different radii on the nonradiative charge trapping and recombination in monolayer InSe. Our results reveal that electron–hole recombination for pristine InSe occurs within several nanoseconds due to the weak nonadiabatic (NA) coupling. Selenide vacancy generates three trap states within the band gap, enhances the NA coupling, and provides new channels for charge carrier relaxation, resulting in the significantly decreased charge carrier recombination time. Passivating the selenide vacancy with anions (O2–, S2–, and Te2–) can eliminate the trap states within the band gap and extend the charge carrier lifetimes because of the decreased NA coupling. Meanwhile, the passivation effect of anions is dramatically dependent on the type of anions, and S2– is more suitable for repairing selenide vacancy than O2– and Te2– because S2– and Se2– have much closer radii. This study provides an atomistic mechanism of the effects of selenide vacancy and anion passivation on the performance of InSe thin-film solar cells and suggests that the choice of anions with a suitable radius is valuable for prolonging the excited-state lifetime

Atomic-Scale Insights into the Activation of Near-Infrared- Responsive Photoactivity in BiOCl Grain Boundaries

Two-dimensional bismuth oxychloride (BiOCl) is a promising semiconductor material in energy production and environmental remediation because of its high surface areas and exposed uncoordinated atoms. However, its development is hindered by the large band gap (∼3.40 eV). In this work, using density functional theory, we have demonstrated that ∑5 (120) and ∑5 (310) grain boundaries (GBs) barely change the electronic structure of pristine BiOCl, while ∑13 (320) GB significantly reduces the transition energy barrier of electron and broadens the optical absorption range to near-infrared (NIR). More importantly, the employed structures are stable and their electronic structures can be well maintained at room temperature, according to the molecular dynamic (MD) simulations. Our results suggest that tuning the types of GBs can significantly improve the ability of optical absorption of the BiOCl photocatalyst and provide an alternative way for designing excellent semiconductor photocatalysts

Atomic-Scale Insights into the Activation of Near-Infrared- Responsive Photoactivity in BiOCl Grain Boundaries

Two-dimensional bismuth oxychloride (BiOCl) is a promising semiconductor material in energy production and environmental remediation because of its high surface areas and exposed uncoordinated atoms. However, its development is hindered by the large band gap (∼3.40 eV). In this work, using density functional theory, we have demonstrated that ∑5 (120) and ∑5 (310) grain boundaries (GBs) barely change the electronic structure of pristine BiOCl, while ∑13 (320) GB significantly reduces the transition energy barrier of electron and broadens the optical absorption range to near-infrared (NIR). More importantly, the employed structures are stable and their electronic structures can be well maintained at room temperature, according to the molecular dynamic (MD) simulations. Our results suggest that tuning the types of GBs can significantly improve the ability of optical absorption of the BiOCl photocatalyst and provide an alternative way for designing excellent semiconductor photocatalysts

Photoinduced Localized Hole Delays Nonradiative Electron–Hole Recombination in Cesium–Lead Halide Perovskites: A Time-Domain Ab Initio Analysis

All-inorganic perovskites have attracted intense interest as promising photovoltaic materials due to their excellent performance. Using time domain density functional theory combined with nonadiabatic (NA) molecular dynamics, we demonstrate that a photoinduced localized polaron-like hole greatly delays the nonradiative electron–hole recombination relative to the structure with delocalized free charge of the CsPbBr₃. This is because localized charge carriers diminish overlap between electron and hole wave functions and decrease the NA coupling by a factor of 6. In addition, polaron formation increases the band gap of CsPbBr₃, slowing down recombination further. The smaller NA coupling and larger band gap compete successfully with the longer decoherence time, extending the recombination to tens of nanoseconds. The calculated recombination times show excellent agreement with experiment. Our study reveals the atomistic mechanisms underlying the suppression of recombination upon formation of localized polaron-like holes and advances our understanding of the excited-state dynamics of all-inorganic perovskite solar cells

Atomic-Scale Insights into the Activation of Near-Infrared- Responsive Photoactivity in BiOCl Grain Boundaries

Two-dimensional bismuth oxychloride (BiOCl) is a promising semiconductor material in energy production and environmental remediation because of its high surface areas and exposed uncoordinated atoms. However, its development is hindered by the large band gap (∼3.40 eV). In this work, using density functional theory, we have demonstrated that ∑5 (120) and ∑5 (310) grain boundaries (GBs) barely change the electronic structure of pristine BiOCl, while ∑13 (320) GB significantly reduces the transition energy barrier of electron and broadens the optical absorption range to near-infrared (NIR). More importantly, the employed structures are stable and their electronic structures can be well maintained at room temperature, according to the molecular dynamic (MD) simulations. Our results suggest that tuning the types of GBs can significantly improve the ability of optical absorption of the BiOCl photocatalyst and provide an alternative way for designing excellent semiconductor photocatalysts

Atomic-Scale Insights into the Activation of Near-Infrared- Responsive Photoactivity in BiOCl Grain Boundaries

Two-dimensional bismuth oxychloride (BiOCl) is a promising semiconductor material in energy production and environmental remediation because of its high surface areas and exposed uncoordinated atoms. However, its development is hindered by the large band gap (∼3.40 eV). In this work, using density functional theory, we have demonstrated that ∑5 (120) and ∑5 (310) grain boundaries (GBs) barely change the electronic structure of pristine BiOCl, while ∑13 (320) GB significantly reduces the transition energy barrier of electron and broadens the optical absorption range to near-infrared (NIR). More importantly, the employed structures are stable and their electronic structures can be well maintained at room temperature, according to the molecular dynamic (MD) simulations. Our results suggest that tuning the types of GBs can significantly improve the ability of optical absorption of the BiOCl photocatalyst and provide an alternative way for designing excellent semiconductor photocatalysts

Atomic-Scale Insights into the Activation of Near-Infrared- Responsive Photoactivity in BiOCl Grain Boundaries

Two-dimensional bismuth oxychloride (BiOCl) is a promising semiconductor material in energy production and environmental remediation because of its high surface areas and exposed uncoordinated atoms. However, its development is hindered by the large band gap (∼3.40 eV). In this work, using density functional theory, we have demonstrated that ∑5 (120) and ∑5 (310) grain boundaries (GBs) barely change the electronic structure of pristine BiOCl, while ∑13 (320) GB significantly reduces the transition energy barrier of electron and broadens the optical absorption range to near-infrared (NIR). More importantly, the employed structures are stable and their electronic structures can be well maintained at room temperature, according to the molecular dynamic (MD) simulations. Our results suggest that tuning the types of GBs can significantly improve the ability of optical absorption of the BiOCl photocatalyst and provide an alternative way for designing excellent semiconductor photocatalysts

Superoxide/Peroxide Chemistry Extends Charge Carriers’ Lifetime but Undermines Chemical Stability of CH₃NH₃PbI₃ Exposed to Oxygen: Time-Domain <i>ab Initio</i> Analysis

Hybrid organic–inorganic perovskites have emerged as very successful optically active materials due to their unique electronic and chemical properties. Experiments have shown that oxygen undermines perovskite chemical stability, but enhances charge carrier lifetimes. Focusing on CH3NH3PbI3, which has become the classic material, we demonstrate how and why charge carrier lifetimes change in the presence of oxygen, by carrying out nonadiabatic molecular dynamics simulations combined with time-domain ab initio density functional theory. Calculations have shown that superoxide and peroxide are the common forms of oxygen interacting with CH3NH3PbI3 and that oxygen most readily interacts with iodine vacancies on the perovskite surface. We establish that the iodine vacancy decreases charge carrier lifetimes, because it localizes both electrons and holes, increasing their overlap. By passivating the vacancy, the oxygen species separate electrons and holes and increase the lifetimes by more than an order of magnitude. Passivating the vacancy by water and Lewis bases, such as pyridine and thiophene, also leads to electron–hole separation. The energy gap changes only by a few percent; however, the nonadiabatic coupling becomes much weaker, and the quantum coherence time decreases significantly. The detailed time-domain atomistic analysis of the excited state dynamics rationalizes why the photogenerated charge carriers in perovskites are robust to defects and interactions with chemical species present in air, such as water and oxygen, even though they undermine perovskite chemical stability. The results can apply to other solar energy materials, which are exposed to atmospheric gases and the performance of which often depends on such exposure