Ultrafast Charge Separation and Recombination across a

Subscriber access provided by CARLETON UNIVERSITY

C: Energy Conversion and Storage; Energy and Charge Transport

Ultrafast Charge Separation and Recombination across a Molecule/CsPbBr Quantum Dot Interface from FirstPrinciples Nonadiabatic Molecular Dynamics Simulation 3

Zhaosheng Zhang, Jinlu He, and Run Long J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.9b04855 • Publication Date (Web): 06 Sep 2019 Downloaded from pubs.acs.org on September 6, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Ultrafast Charge Separation and Recombination across a Molecule/CsPbBr3 Quantum Dot Interface from First-Principles Nonadiabatic Molecular Dynamics Simulation Zhaosheng Zhang,1 Jinlu He,1 Run Long1 1College

of Chemistry, Key Laboratory of Theoretical & Computational Photochemistry of

Ministry of Education, Beijing Normal University, Beijing, 100875, P. R. China

ABSTRACT: All inorganic perovskite quantum dots (QDs) hold great promise in photovoltaic solar cells. While the reduced dimensionality of QDs confines the photoexcited electron-hole pairs, suppresses charge separation, and accelerates charge recombination (CR), limiting the photon-toelectron conversion efficiency of a solar cell. Molecule passivation can overcome this shortcoming via efficiently extracting charge carriers from QDs. Using a combination of time-domain density functional theory and nonadiabatic (NA) molecular dynamics, we demonstrate that low-frequency vibrations promoted both charge separation and recombination. The photoexcited excitons on a CsPbBr3 QD can efficiently dissociate into free charge carriers via rapid interfacial electron (ET) and hole transfer (HT) to a binding benzoquinone (BQ) or phenothiazine (PTZ) molecule on similar sub-100 ps timescales, respectively. This is manifested by the fact that the QD-BQ system holds smaller energy gap and NA coupling between the donor and acceptor states than the QD-



Corresponding author, E-mail: [email protected] 1

ACS Paragon Plus Environment

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

PTZ system, while small energy gap accelerates charge transfer and small coupling delays dynamics. The interplay between the two factors leads to balance ET and HT in the QD-BQ and QD-PTZ systems. In contrast, CR in the QD-BQ system happens 5 times slower than the QD-PTZ system, achieving carriers lifetime about 4 ns and sub-1 ns respectively. This is because CR in the former system experiences a wider energy gap and a weaker NA coupling and which compete successfully with the longer decoherence time, delaying the recombination by a factor of about 5 compared to the latter system. All the obtained timescales agree well with experiment. The study suggests that QDs passivation with molecules indeed favor charge separation and suppress charge recombination by affecting electron-vibrational interactions and energy gap, and advance our understanding of photoexcitation dynamics in perovskite QDs and molecule hybrid systems.

2


Page 2 of 30

Page 3 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1. Introduction All inorganic cesium lead halide CsPbX3 (X = Cl, Br, I) perovskites1 have emerged as promising photovoltaic materials due to their excellent electronic and optical properties, such as large carrier diffusion lengths2 and high thermal stabilities.3-4 However, CsPbX3 perovskites are typically in disordered structure or in quantum dots (QDs) because the size of Cs+ ion is not large enough to remain the perfect Pb-I octahedron. CsPbX3 QDs carry additional advantages, including tunable band gap that is easily realized by changing the chemical composition rather than by size variation,5-6 narrow emission spectrum,7 and high photoluminescence quantum yield8-12 arising due to quantum confinement effects. These excellent properties enable CsPbX3 QDs utilizing as light-emitting diodes (LEDs),13-15 nonlinear optical devices,16-18 bioimaging,19 and solar cells.20-21 Furthermore, the unique hot phonon bottleneck in QDs, originating from large inter-level spacing that results in inefficient photon emissions, can slow down carriers cooling on tens of picoseconds.22-24 Using the property, the power conversion efficiency can be progressively improved in the so-called hot-carrier solar cells because which can overcome the ShockleyQueisser limit by harvesting excess energy of photogenerated hot carriers.24 However, QDs generally contain high density surface defects that usually constitute nonradiative channels for charge and energy losses. Even worse, Auger-type recombination becomes significant in the presence of high defect density and high excitation densities, providing the channels for exchanging energy between electrons and holes, and accelerating energy loss further. High density 3



defects also accelerate degradation of QDs films exposure to light- and thermal-irradiation. In addition, photo-created electrons and holes are spatially confined inside QDs and are hard to separate, leading to a high recombination rate and a short excited-state lifetime. Synthesis of coreshell nanoparticles can partially passivate defects and enhance QDs' stability. This core-shell structure also facilitates charge separation with formation of a type-II band alignment heterojunction.25-26 However, it challenges experimental techniques because which have to be precise control of the boundary morphology between the core and shell. Alternatively, surface passivation QDs by ligands, such as organic molecules, provide another effective approach to heal defects, favor charge transfer, and obtain high photoluminescence quantum yield with unprecedented operational stability in ambient conditions.27-29 In order to improve further the performance of perovskites photovoltaic and optoelectronic devices, mechanistic understanding of photophysical processes in the perovskite materials and devices becomes an emerging task. Using ultrafast transient absorption spectroscopy, Lian and coworkers30 have recently shown that photoexcited excitons (bounded electron-hole pairs) on CsPbBr3 QDs can be efficiently dissociated into free electrons and holes via electron (ET) and hole transfer (HT) on simlar tens of picoseconds, in the presence of benzoquinone (BQ) as electron acceptor and phenothiazine (PTZ) as hole acceptor, respectively.30 In contrast, charge recombination (CR) takes place on much slower in both systems, occurring on several nanoseconds in the QD-BQ system while on sub-nanoseconds in the QD PTZ system.30 The same 4


Page 4 of 30

Page 5 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


group has shown that the charge-separated state lifetimes can be prolonged over 100 nanoseconds if replacing (quasi-) zero-dimensional QDs with (quasi-) two-dimensional nanoplatelets because photoexcited electrons and holes are well separated.31 Correspondingly, ET and HT timescales are delayed to several hundred picoseconds due to decreased donor-acceptor coupling.31 The experimental observations raise two questions: 1) why ET and HT proceed on similar timescales while the timescale in CR differs by a factor about 5 in the CsPbBr3 QD-BQ and CsPbBr3 PTZ systems, 2) why CR is 2-3 order magnitude slower than ET and HT?

30

However, the factors

responsible for the experimental observations remain unclear. Our previous works on perovskites and/or QDs have demonstrated that the charge transfer and recombination are influenced by several complicated factors,32-34 and therefore, understanding of photoexcitation charge dynamics in the CsPbBr3 QD-BQ and CsPbBr3 QD PTZ systems requires a comprehensive theoretical study in the time-domain and at the atomistic level. Stimulated by recent experiment,30 charge transfer and recombination in the CsPbBr3 QDBQ and CsPbBr3 QD-PTZ systems are investigated by nonadiabatic molecular dynamics (NAMD) simulations in order to establish the influence factors for the photoexcitation charge dynamics. The simulations confirm the experimental observations that ET in the CsPbBr3 QD-BQ system and HT in the CsPbBr3 QD-PTZ system occur on similar sub-100 ps timescales, which were followed by CR in the former case proceeding several times slower than the latter case, extending charge carriers lifetime to several nanoseconds. For ET, the electron donor and acceptor states are well 5



localized on the CsPbBr3 QD and BQ, leading to a small NA electron-phonon coupling. For HT, the hole donor state is delocalized on both the QD and PTZ and the hole acceptor state is fully localized on the PTZ molecule. Large mixing of two components of hole donor state wave functions gives rise to an enhanced NA coupling, accelerating HT. At the same time, larger energy gap for HT than ET suppresses the former process. Finally, phonon-induced quantum decoherence times for ET and HT are similar and their influence on the difference between two charge transfer timescales becomes negligible. Consequently, the joint influence of energy gap and NA coupling leads to ET and HT timescales in the balance. For CR process, the donor and acceptor states are separated by a larger energy gap in the QD-BQ system compared with the QD-PTZ system. Typically, small energy gap favors mixing of two wave functions and enhancement of NA coupling. Significant atomic fluctuations, arising due to more flexible PTZ molecule relative to the BQ molecule, accelerate quantum decoherence process. As a result, electron-hole recombination in the QD-BQ system is delayed by a factor of about 5 compared with the QD-PTZ system due to smaller NA coupling and larger energy gap competing successfully with longer decoherence time. The obtained timescales for ET, HT and CR agree well with the experimental data.30 Our study establishes a mechanistic understanding of the photoexcitation charge dynamics in the molecule passivated CsPbBr3 QD systems.

2. Simulation Methodology 6


Page 6 of 30

Page 7 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


The simulations are performed with the quantum-classical decoherence induced surface hopping (DISH) NAMD,35-37 implemented with time-dependent Kohn-Sham density functional theory framework.38 In this approach, lighter and faster electrons are described quantum mechanically while heavier and slower nuclei are treated (semi)classically. DISH not only has the inherent advantages of the fewest switch surface hopping algorithm,39-40 but also includes the quantum decoherence effect arising due to the nuclei wave function branching. Decoherence correction is needed here because quantum transitions across a pair of states separated by a wide energy gap take place slower than decoherence time. And also the decoherence times are typically on sub-100 fs in condensed-phase materials,34, 41-42 which are extremely shorter than the charge separation and recombination times scales in the present systems, corresponding to sub-100 ps and several nanoseconds respectively.30 Decoherence, known as pure-dephasing in the optical response theory, whose time is computed using the second-order cumulant approximation.43 This quantumclassical approximation approach has applied to study photoexcitation dynamics in a broad range of systems,41,

44-50

including perovskites containing grain boundaries,34,

46-47

passivating with

oxygen,48 and forming a heterojunction with two-dimensional material,49 and ordered and disordered structures.50 Geometry optimization, adiabatic MD and NA coupling are calculated using the Vienna ab initio simulation package (VASP).51-52 The Perdew-Burke-Ernzerhof (PBE) functional53 is employed to describe the electronic exchange-correlation interactions and the projectoraugmented wave approach is used to treat the electron-core interactions.54 In order to obtain 7



reasonably accurate energy gap between pair of electronic states, the DFT+U approach is adopted to describe the local properties of C 2p, O 2p and S 3p electrons. In particular, an on-site U value of 18.0 eV is applied to the C 2p and O 2p orbitals in the QD-BQ system and U=1.0 eV is chosen to act on the C 2p, N 2p and S 3p orbitals in the QD-PTZ system w, respectively. The energy cutoff of plane wave is set to 400 eV to converge the energy. Geometry optimization stops until the force acting on each atom is less than 10-3 eV·Å-1. The DFT-D3 method is employed to describe the weak intermolecular van der Waals interactions during structural optimization and adiabatic MD.55-57 After geometry optimization at 0 K, the 52-atom CsPbBr3-BQ and 63-atom CsPbBr3PTZ systems were heated to 300 K lasting 2 ps by repeated velocity rescaling. Then, 10 ps adiabatic MD trajectories were generated at 300 K in the microcanonical ensemble within a 1 fs time step. To simulate the charge transfer and recombination, 2000 geometries were selected randomly from the 10 ps adiabatic MD trajectories as the initial conditions for NAMD calculations by the PYXAID.36-37 Refs36-37 give the NAMD algorithm in detail.

3. Results and Discussion 3.1 Geometric and Electronic Structure The 40-atom CsPbBr3 QD was taken from our previous work.58 BQ or PTZ molecule binds to the edge Pb atom of the QD via O-Pb and S-Pb covalent bond, leading to formation of the CsPbBr3 QD-BQ and CsPbBr3 QD-PTZ systems, respectively (Figure 1). Left panel of Figure 1 8


Page 8 of 30

Page 9 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


shows that the optimized CsPbBr3 QD-BQ (Figure 1a) and CsPbBr3 QD-PTZ (Figure 1b). The calculated Pb-O bond length of 2.910 Å is shorter than the Pb-S bond length of 3.370 Å, arising due to the larger S ion size. The calculated average Pb-Br bond lengths of about 2.952 Å in the two systems are almost identical, indicating that the adsorbed molecules perturb the QD structure slightly at 0 K. At room temperature, thermal fluctuations significantly perturb the geometries (right panel of Figure 1), in particular,

deformation and distortion of the PTZ molecule and the

QD in the CsPbBr3 QD-PTZ system are notably stronger than the CsPbBr3 QD-BQ system because the longer PTZ is much more flexible compared with the BQ and affect the geometry more strongly. The canonically averaged bond length of Pb-O and Pb-S becomes 2.813 Å and 3.151 Å, while the canonically averaged Pb-Br bond length increases to 2.965 Å and 2.991 Å in the CsPbBr3 QD-BQ and CsPbBr3 QD-PTZ systems, respectively. The significant variation in bond length and geometry distortion of the CsPbBr3 QD-PTZ system upon heating alter the electron-phonon coupling and thus affect charge dynamics.

9



Figure 1. Simulation cell showing the geometry of (a) CsPbBr3 QD-BQ and (b) CsPbBr3 QD-PTZ at 0 K (left panel) and room temperature (right panel). Thermal fluctuations have a significant influence on the geometries, especially for the CsPbBr3 QD-PTZ system, and hence, modulate the electron-phonon interaction.

Figure 2 demonstrates the projected density of states (PDOS) of CsPbBr3 QD-BQ and CsPbBr3 QD-PTZ. For the CsPbBr3 QD-BQ system, photoexcitation CsPbBr3 QD promotes an electron from its highest occupied (HOMO) to its lowest unoccupied molecular orbital (LUMO), which is followed ET from the QD LUMO to the BQ LUMO and subsequent between the BQ LUMO and QD HOMO (Figure 2a), corresponding to an energy gap of 1.08 eV 1.70 eV, respectively. Similarity, in case of the CsPbBr3 QD-PTZ system, HT takes places between the QD HOMO and PTZ HOMO across a 0.82 eV energy gap, while CR occurs between the QD LUMO 10


Page 10 of 30

Page 11 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


and PTZ HOMO across a broad energy gap of 1.83 eV (Figure 2b). Considering the relative positions of band edges of the CsPbBr3 QD, BQ, and PTZ molecules reported experimentally,30 we scaled the above energy gaps to experimental data for NAMD simulations, corresponding to 0.68 eV for ET, 2.06 eV for CR in the CsPbBr3-BQ, 0.86 eV for HT, and 1.88 eV for CR in the CsPbBr3-PTZ, Table 1.30 Generally, smaller band gap favors stronger NA coupling and faster nonradiative relaxation because they bring the electronic and vibrational quanta closer to resonance. The strength of NA coupling is reflected by the overlap between the donor and acceptor states wave functions. Part c and d of Figure 2 display the charge densities of the key states involving in the charge transfer and recombination. The overlap between pair of key states in the CsPbBr3 QD-PTZ is generally larger than the CsPbBr3 QD-BQ, leading to stronger NA coupling for each process, Table 1. In case of ET, Figure 2c shows that the donor state (QD LUMO) and acceptor state (BQ LUMO) are entirely localized on the CsPbBr3 QD and BQ molecule, which reduce wave function mixing and NA electron-phonon coupling. In contrast , Figure 2d indicates that for HT the donor state (QD HOMO) is delocalized on both CsPbBr3 QD and PTZ (Figure 2d), while the acceptor state (PTZ HOMO) is localized on itself. Lager mixing in wave functions leads to stronger NA coupling. As a result, the averaged absolute value of NA coupling for ET of 1.15 meV in the CsPbBr3 QD-BQ is smaller than the coupling for HT of 1.42 meV in the CsPbBr3PTZ, Table 1. Following ET, electron-hole recombination occurs between the donor state BQ LUMO and 11



acceptor state QD HOMO in the CsPbBr3 QD-BQ system. The fully localized donor state is away from the fully localized acceptor state (Figure 2c). Alternatively, electron-hole recombination following HT takes place across the donor state QD LUMO and acceptor state PTZ HOMO in the CsPbBr3 QD-BQ system. The donor and acceptor states are well localized on the CsPbBr3 QD and PTZ molecule (Figure 2d). However, one should note that small energy gap facilitates electronic and vibrational quantum in resonance. The energy gap of 1.88 eV between the QD LUMO and PTZ HOMO is smaller than that the BQ LUMO and QD HOMO energy gap of 2.06 eV, serving to explain the larger NA coupling1.17 meV in the CsPbBr3 QD-PTZ system compared with 0.97 meV in the CsPbBr3 QD-BQ system, Table 1. Strong NA coupling accelerates charge transfer and recombination. Cs8Pb8Br24 used in the current simulation and whose properties are well-studied in our previous work.58 The QD remains the stoichiometry and has not defect states. One may expect that surface passivation with organic ligands should affect notably the electronic properties of CsPbBr3 QD. Experiments show that CsPbBr3 QDs passivation with organic ligands only change the fundamental bandgap within tens of microelectronvolt59-60 because ligands do not contribute to the band edge states.61 Molecules are analogy to ligands somehow for stabilizing the QDs and “healing” the surface, which prefer binding to an under-coordinated atom of a QD or exchanging with organic ligands for achieving chemical adsorption. Surface ligands would increase the moleculesQD separation and decrease the donor-acceptor electron-phonon coupling. The created energy barrier would suppress both electron and hole transfer as well as electron-hole recombination. Like 12


Page 12 of 30

Page 13 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the well-studied “magic” Cd33Se33 cluster, Prezhdo and coauthors showed that passivating the surface by ligands does not change the fundamental gap of relaxed Cd33Se33.62 NAMD simulations are usually using the model by coordinating the conjugate organic subsystem directly with the inorganic QD.63-64 The significant computational efforts for NAMD simulations do not allow us to study ligand explicitly at the ab initio time-domain level of description.

Figure 2. Projected density of states (PDOS) of (a) CsPbBr3 QD-BQ and (b) CsPbBr3 QD-PTZ calculated using the optimized geometries, separated contributions into CsPbBr3 QD, BQ, and PTZ components. Zero energy is set to the Fermi level. The charge densities of key electronic states involving in the ET/HT and CR of (c) CsPbBr3 QD-BQ and (d) CsPbBr3 QD-PTZ. The CsPbBr3 QD LUMO (QD HOMO) and BQ LUMO (PTZ HOMO) constitute the donor and acceptor states for ET (HT). While the BQ LUMO (QD LUMO) and QD HOMO (PTZ HOMO) are the donor and acceptor state for CR in the CsPbBr3 QD-BQ (CsPbBr3 QD-PTZ) systems, respectively. The averaged absolute NA couplings for each pair of states are summarized in Table 1. 13



3.2 Electron-Vibrational Interactions Electron-vibrational interactions generate elastic scattering and inelastic scattering. Both of them affect charge relaxation dynamics. Inelastic scattering causes energy exchange between electrons and phonons and leads to electronic energy dissipation into heat during the transition between a pair of electronic states. Elastic electron-phonon scattering destroys the coherence of superpositions formed between two states via NA coupling. Elastic electron-phonon scattering, known as decoherence, is analogy to the pure-dephasing in the optical response theory.43 Figure 3 shows the spectral density, computed by performing the Fourier transform (FT) of the autocorrelation functions for energy gap fluctuation of two states, which characterizes the phonon modes coupling to electronic degrees of freedom and participating in charge transfer and recombination. Figure 3a demonstrates the spectral density for ET (top panel) and CR (bottom panel) in the CsPbBr3 QD-BQ system, while Figure 3b illustrates the spectral density for HT (top panel) and CR (bottom panel) in the CsPbBr3 QD-PTZ system. Low frequency vibrations below 300 cm-1 dominate the whole spectral densities in both systems. In particular, the peaks within a 50 ~ 175 cm-1 frequency range can be assigned to Raman-active modes stemming from the lattice vibrations of the [PbBr6]4- octahedron.65 The peak near 300 cm-1 is associated with the Pb-O vibration modes (Figure 3a),66-67 while the peak around 200 cm-1 can be attributed to the Pb-S bond vibrations (Figure 3b).68-69 These phonon modes create the majority of NA coupling and lead to charge transfer and recombination in the two systems. 14


Page 14 of 30

Page 15 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3. Spectral densities obtained from Fourier transforms of autocorrelation functions for the fluctuations of the energy gap of pair of electronic states of (a) CsPbBr3 QD-BQ and (b) CsPbBr3 QD-PTZ. Here, ET/HT are in red line while CR is in black line.

The pure-dephasing function can be calculated using the second-order cumulant approximation in the optical spectroscopy,43 Figure 4. Fitting the functions to a Gaussian, exp [ ― 0.5( ―𝑡/𝜏)2], gives dephasing times, τ, in Table 1. The pure-dephasing time is very short, serving to slow charge dynamics. The sub-5 fs pure-dephasing time are much shorter than the charge transfer and recombination time scales measured experimentally,30 and thus it is essential to consider the decoherence effect in the present NAMD simulations. To rationalize the difference in pure-dephasing times, we compute the unnormalized autocorrelation functions (un-ACF), inset 15



of Figure 4 and whose initial value characterizes the energy gap fluctuation squared. In general, larger initial value of the un-ACF and faster decoherence.70 Shown in the insets of Figure 4a and 4b, the initial value of the four un-ACFs follows the order HT > ET > CR CR in the CsPbBr3 QDPTZ > CR in the CsPbBr3 QD-BQ, leading to that the pure-dephasing time decreases as the same sequence (Table 1), 2.08 fs, 2.26 fs, 2.32 fs, and 3.75 fs, respectively. Decoherence is a timedomain analog of Franck-Condon factor in energy-domain.71 Faster decoherence means smaller Franck-Condon factor and thus lower quantum transition rate.

Figure 4. Pure-dephasing functions for the pair of key electronic states (a) CsPbBr3 QD-BQ and (b) CsPbBr3 QD-PTZ. The pure-dephasing times are summarized in Table 1, obtained by Gaussians fitting. The inset shows the unnormalized autocorrelation function. Here, ET/HT are in red line while CR is in black line.

3.3 Charge Separation and Recombination

16


Page 16 of 30

Page 17 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5 demonstrates the evolution of the population of the donor state for ET, HT and CR in the two systems under investigation. Fitting the data using the short-time linear approximation to the exponential function, 𝑃(𝑡) = 𝑒𝑥𝑝( ―𝑡 𝜏) ≈ 1 ― (𝑡 𝜏), obtains the time scales τ, summarized in Table 1. ET in the CsPbBr3-BQ proceeds slightly slower than HT in the CsPbBr3-PTZ, 62 ps vs 51 ps. The two timescales are very closer to each other and agree well with the experimentally measured ET (65  5 ps) and HT (49  6) timescales.30 Decoherence has little influence on ET and HT because the pure-dephasing times are almost identical for the two processes, Table 1. In turn, the interplay between NA coupling and energy gap governs the transition rate, which is proportional to the NA coupling squared. The ratio of the NA coupling squared between HT and ET is 1.5. The ratio of the rates is slightly smaller, 1.2, because of energy gap. In contrast, the computed timescales for CR in the CsPbBr3 QD-BQ is almost 5 times longer than that in the CsPbBr3 QD-PTZ, 4100 ps vs 830 ps, which again show excellent agreement with experiment,30 Table1. The enhancement of charge carriers lifetime by a factor of about 5 can be rationalized by the competition between small NA coupling 0.97 meV, large energy gap of2.06 eV, and long dcoherence time 3.75 fs , Table 1. On the one hand, ET and HT timescales are almost identical on sub-100 ps. On the other hand, a factor of about 5 change in the charge carriers lifetime is relatively large. When designing of high-performance perovskite solar cells, one should consider not only fast charge separation but also slow recombination. Fast charge separation via ET or HT favors breaking excitons into free electrons and holes, enhancing photocurrent. Slow nonradiative electron-hole recombination favors reducing charge and energy losses to heat. Achieving the two 17



Page 18 of 30

goals needs rational choice of passivated molecules during design of perovskite QD solar cells.

Figure 5. ET (red line) and CR (black line) in (a) CsPbBr3 QD-BQ and HT (red line) and CR (black line) in (b) CsPbBr3 QD-PTZ. The black and red lines correspond to the left-hand side vertical axis and righthand size vertical axis respectively. The data given in Table 1 rationalize the population decay trend. Table 1. Energy gap, average absolute NA coupling, pure-dephasing time, and nonradiative relaxation timescales for electron (ET) and hole transfer (HT) and charge recombination (CR) of the CsPbBr3 QD-BQ and CsPbBr3 QD-PTZ systems. The data in parentheses are experimental values.30

QD-BQ

QD-PTZ

Energy gap

NA coupling

pure-dephasing

relaxation

(eV)

(meV)

(fs)

(ps)

ET

0.68

1.15

2.26

62 (65  5)

CR

2.06

0.97

3.75

HT

0.86

1.42

2.08

CR

1.88

1.17

2.32

18


4100 (2600  400) 51(49  6) 830 (1000  200)

Page 19 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


4. Conclusion We investigated charge transfer and recombination in CsPbBr3 QD- BQ and CsPbBr3 QDPTZ systems, using a combination of time-domain density functional and NAMD. The simulations demonstrate that photoexcited electron and hole on CsPbBr3 QD can be successfully extracted by BQ and PTZ molecule respectively on similar sub-100 ps timescales. The almost same ET and HT timescales are attributed to the interplay between the NA coupling and energy gap, because the nearly identical decoherence times have little influence on quantum transition rate. In contrast, electron-hole recombination timescale in the CsPbBr3 QD-BQ system is about 5 times longer than the CsPbBr3-PTZ systems, extending excited charge carriers lifetime to several nanoseconds. A factor of about 5 increase in carriers lifetime is rationalized by the smaller NA coupling and larger energy gap in the QD-BQ system than the QD-PTZ system. Charge couples to low-frequency phonons within a 50-300 cm-1 range. The reported observations agree with the available experiment.30 The study advances our understanding of the key factors affecting and controlling the photoexcitation charge dynamics of perovskite QDs passivated by difference molecules.

Notes The authors declare no competing financial interest.

Acknowledgements R. L. acknowledges financial support by the National Science Foundation of China, grant 19



nos. 21573022 and 51861135101, the Fundamental Research Funds for the Central Universities, the Recruitment Program of Global Youth Experts of China, and the Beijing Normal University Startup.

20


Page 20 of 30

Page 21 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


References (1) Yakunin, S.; Protesescu, L.; Krieg, F.; Bodnarchuk, M. I.; Nedelcu, G.; Humer, M.; De Luca, G.; Fiebig, M.; Heiss, W.; Kovalenko, M. V. Low-Threshold Amplified Spontaneous Emission and Lasing from Colloidal Nanocrystals of Cesium Lead Halide Perovskites. Nat. Commun. 2015, 6, 8056. (2) Yettapu, G. R.; Talukdar, D.; Sarkar, S.; Swarnkar, A.; Nag, A.; Ghosh, P.; Mandal, P. Terahertz Conductivity within Colloidal CsPbBr3 Perovskite Nanocrystals: Remarkably High Carrier Mobilities and Large Diffusion Lengths. Nano Lett. 2016, 16, 4838-4848. (3) Sutton, R. J.; Eperon, G. E.; Miranda, L.; Parrott, E. S.; Kamino, B. A.; Patel, J. B.; Hörantner, M. T.; Johnston, M. B.; Haghighirad, A. A.; Moore, D. T. Bandgap-Tunable Cesium Lead Halide Perovskites with High Thermal Stability for Efficient Solar Cells. Adv. Energy Mater. 2016, 6, 1502458. (4) Beal, R. E.; Slotcavage, D. J.; Leijtens, T.; Bowring, A. R.; Belisle, R. A.; Nguyen, W. H.; Burkhard, G. F.; Hoke, E. T.; McGehee, M. D. Cesium Lead Halide Perovskites with Improved Stability for Tandem Solar Cells. J. Phys. Chem. Lett. 2016, 7, 746-751. (5) Song, J.; Li, J.; Li, X.; Xu, L.; Dong, Y.; Zeng, H. Quantum Dot Light-Emitting Diodes Based on Inorganic Perovskite Cesium Lead Halides (CsPbX3). Adv. Mater. 2015, 27, 7162-7167. (6) Swarnkar, A.; Chulliyil, R.; Ravi, V. K.; Irfanullah, M.; Chowdhury, A.; Nag, A. Colloidal CsPbBr3 Perovskite Nanocrystals: Luminescence Beyond Traditional Quantum Dots. Angew. Chem. Int. Ed. 2015, 127, 15644-15648. (7) Shinde, A.; Gahlaut, R.; Mahamuni, S. Low-Temperature Photoluminescence Studies of CsPbBr3 Quantum Dots. J. Phys. Chem. C 2017, 121, 14872-14878. (8) Wang, Y.; Zhi, M.; Chan, Y. Delayed Exciton Formation Involving Energetically Shallow 21



Trap States in Colloidal CsPbBr3 Quantum Dots. J. Phys. Chem. C 2017, 121, 28498-28505. (9) de Jong, E. M.; Yamashita, G.; Gomez, L.; Ashida, M.; Fujiwara, Y.; Gregorkiewicz, T. Multiexciton Lifetime in All-Inorganic CsPbBr3 Perovskite Nanocrystals. J. Phys. Chem. C 2017, 121, 1941-1947. (10)Kumawat, N. K.; Swarnkar, A.; Nag, A.; Kabra, D. Ligand Engineering to Improve the Luminance Efficiency of CsPbBr3 Nanocrystal Based Light-Emitting Diodes. J. Phys. Chem. C 2018, 122, 13767-13773. (11)Bi, C.; Wang, S.; Wen, W.; Yuan, J.; Cao, G.; Tian, J. Room-Temperature Construction of Mixed-Halide Perovskite Quantum Dots with High Photoluminescence Quantum Yield. J. Phys. Chem. C 2018, 122, 5151-5160. (12)Begum, R.; Parida, M. R.; Abdelhady, A. L.; Murali, B.; Alyami, N. M.; Ahmed, G. H.; Hedhili, M. N.; Bakr, O. M.; Mohammed, O. F. Engineering Interfacial Charge Transfer in CsPbBr3 Perovskite Nanocrystals by Heterovalent Doping. J. Am. Chem. Soc. 2017, 139, 731-737. (13)Shirasaki, Y.; Supran, G. J.; Bawendi, M. G.; Bulović, V. Emergence of Colloidal QuantumDot Light-Emitting Technologies. Nat. Photonics 2013, 7, 13-23. (14)Wang, H. C.; Lin, S. Y.; Tang, A. C.; Singh, B. P.; Tong, H. C.; Chen, C. Y.; Lee, Y. C.; Tsai, T. L.; Liu, R. S. Mesoporous Silica Particles Integrated with All-Inorganic CsPbBr3 Perovskite Quantum-Dot Nanocomposites (MP-PQDs) with High Stability and Wide Color Gamut Used for Backlight Display. Angew. Chem. Int. Ed. 2016, 55, 7924-7929. (15)Ramasamy, P.; Lim, D.-H.; Kim, B.; Lee, S.-H.; Lee, M.-S.; Lee, J.-S. All-Inorganic Cesium Lead Halide Perovskite Nanocrystals for Photodetector Applications. Chem. Commun. 2016, 52, 2067-2070. (16)Sun, S.; Yuan, D.; Xu, Y.; Wang, A.; Deng, Z. Ligand-Mediated Synthesis of Shape22


Page 22 of 30

Page 23 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Controlled Cesium Lead Halide Perovskite Nanocrystals via Reprecipitation Process at Room Temperature. ACS Nano 2016, 10, 3648-3657. (17)Klimov, V.; Mikhailovsky, A.; Xu, S.; Malko, A.; Hollingsworth, J.; Leatherdale, C.; Eisler, H.-J.; Bawendi, M. Optical Gain and Stimulated Emission in Nanocrystal Quantum Dots. Science 2000, 290, 314-317. (18)Yang, B.; Zhang, F.; Chen, J.; Yang, S.; Xia, X.; Pullerits, T.; Deng, W.; Han, K. Ultrasensitive and Fast All-Inorganic Perovskite-Based Photodetector via Fast Carrier Diffusion. Adv. Mater. 2017, 29, 1703758. (19)Chan, W. C.; Nie, S. Quantum Dot Bioconjugates for Ultrasensitive Nonisotopic Detection. Science 1998, 281, 2016-2018. (20)Nozik, A. J.; Beard, M. C.; Luther, J. M.; Law, M.; Ellingson, R. J.; Johnson, J. C. Semiconductor Quantum Dots and Quantum Dot Arrays and Applications of Multiple Exciton Generation to Third-Generation Photovoltaic Solar Cells. Chem. Rev. 2010, 110, 6873-6890. (21)Yantara, N.; Bhaumik, S.; Yan, F.; Sabba, D.; Dewi, H. A.; Mathews, N.; Boix, P. P.; Demir, H. V.; Mhaisalkar, S. Inorganic Halide Perovskites for Efficient Light-Emitting Diodes. J. Phys. Chem. Lett. 2015, 6, 4360-4364. (22)Mondal, A.; Aneesh, J.; Ravi, V. K.; Sharma, R.; Mir, W. J.; Beard, M. C.; Nag, A.; Adarsh, K. Ultrafast Exciton Many-Body Interactions and Hot-Phonon Bottleneck in Colloidal Cesium Lead Halide Perovskite Nanocrystals. Phys. Rev. B 2018, 98, 115418. (23)Chen, J.; Messing, M. E.; Zheng, K.; Pullerits, T. Cation Dependent Hot Carrier Cooling in Halide Perovskite Nanocrystals. J. Am. Chem. Soc. 2019, 3532-3540. (24)Li, M.; Bhaumik, S.; Goh, T. W.; Kumar, M. S.; Yantara, N.; Grätzel, M.; Mhaisalkar, S.; Mathews, N.; Sum, T. C. Slow Cooling and Highly Efficient Extraction of Hot Carriers in 23



Colloidal Perovskite Nanocrystals. Nat. Commun. 2017, 8, 14350. (25)Wang, S.; Bi, C.; Yuan, J.; Zhang, L.; Tian, J. Original Core–Shell Structure of Cubic CsPbBr3@Amorphous CsPbBrx Perovskite Quantum Dots with a High Bue Photoluminescence Quantum Yield of over 80%. ACS Energy Lett. 2017, 3, 245-251. (26)Zhong, Q.; Cao, M.; Hu, H.; Yang, D.; Chen, M.; Li, P.; Wu, L.; Zhang, Q. One-Pot Synthesis of Highly Stable CsPbBr3@SiO2 Core-Shell Nanoparticles. ACS Nano 2018, 12, 8579-8587. (27)Pan, J.; Sarmah, S. P.; Murali, B.; Dursun, I.; Peng, W.; Parida, M. R.; Liu, J.; Sinatra, L.; Alyami, N.; Zhao, C. Air-Stable Surface-Passivated Perovskite Quantum Dots for Ultra-Robust, Single-and Two-Photon-Induced Amplified Spontaneous Emission. J. Phys. Chem. Lett. 2015, 6, 5027-5033. (28)Pan, J.; Quan, L. N.; Zhao, Y.; Peng, W.; Murali, B.; Sarmah, S. P.; Yuan, M.; Sinatra, L.; Alyami, N. M.; Liu, J. Highly Efficient Perovskite-Quantum-Dot Light-Emitting Diodes by Surface Engineering. Adv. Mater. 2016, 28, 8718-8725. (29)Li, J.; Xu, L.; Wang, T.; Song, J.; Chen, J.; Xue, J.; Dong, Y.; Cai, B.; Shan, Q.; Han, B. 50Fold EQE Improvement up to 6.27% of Solution-Processed All-Inorganic Perovskite CsPbBr3 QLEDs via Surface Ligand Density Control. Adv. Mater. 2017, 29, 1603885. (30)Wu, K.; Liang, G.; Shang, Q.; Ren, Y.; Kong, D.; Lian, T. Ultrafast Interfacial Electron and Hole Transfer from CsPbBr3 Perovskite Quantum Dots. J. Am. Chem. Soc. 2015, 137, 1279212795. (31)Li, Q.; Lian, T. Ultrafast Charge Separation in Two-Dimensional CsPbBr3 Perovskite Nanoplatelets. J. Phys. Chem. Lett. 2019, 10, 566-573. (32)Jankowska, J.; Long, R.; Prezhdo, O. V. Quantum Dynamics of Photogenerated Charge Carriers in Hybrid Perovskites: Dopants, Grain Boundaries, Electric Order, and Other Realistic 24


Page 24 of 30

Page 25 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Aspects. ACS Energy Lett. 2017, 2, 1588-1597. (33)Long, R.; Fang, W.-H.; Prezhdo, O. V. Strong Interaction at the Perovskite/TiO2 Interface Facilitates Ultrafast Photoinduced Charge Separation: A Nonadiabatic Molecular Dynamics Study. J. Phys. Chem. C 2017, 121, 3797-3806. (34)Long, R.; Liu, J.; Prezhdo, O. V. Unravelling the Effects of Grain Boundary and Chemical Doping on Electron-Hole Recombination in CH3NH3PbI3 Perovskite by Time-Domain Atomistic Simulation. J. Am. Chem. Soc. 2016, 138, 3884-3890. (35)Jaeger, H. M.; Fischer, S.; Prezhdo, O. V. Decoherence-Induced Surface Hopping. J. Chem. Phys. 2012, 137, 22A545. (36)Akimov, A. V.; Prezhdo, O. V. The PYXAID Program for Non-Adiabatic Molecular Dynamics in Condensed Matter Systems. J. Chem. Theory Comput. 2013, 9, 4959-4972. (37)Akimov, A. V.; Prezhdo, O. V. Advanced Capabilities of the PYXAID Program: Integration Schemes, Decoherence Effects, Multiexcitonic States, and Field-Matter Interaction. J. Chem. Theory Comput. 2014, 10, 789-804. (38)Kohn, W.; Sham, L. J. Self-Consistent Equations Including Exchange and Correlation Effects. Phys. Rev. 1965, 140, A1133. (39)Tully, J. C. Molecular Synamics with Electronic Transitions. J. Chem. Phys. 1990, 93, 10611071. (40)Parandekar, P. V.; Tully, J. C. Mixed Quantum-Classical Equilibrium. J. Chem. Phys. 2005, 122, 094102. (41)Long, R.; Fang, W.; Akimov, A. V. Nonradiative Electron-Hole Recombination Rate Is Greatly Reduced by Defects in Monolayer Black Phosphorus: Ab Initio Time Domain Study. J. Phys. Chem. Lett. 2016, 7, 653-659. 25



(42)Long, R.; Fang, W.; Prezhdo, O. V. Moderate Humidity Delays Electron-Hole Recombination in Hybrid Organic-Inorganic Perovskites: Time-Domain Ab Initio Simulations Rationalize Experiments. J. Phys. Chem. Lett. 2016, 7, 3215-3222. (43)Mukamel, S., Principles of Nonlinear Optical Spectroscopy; Oxford University Press: New York, 1995. (44)Chaban, V. V.; Prezhdo, V. V.; Prezhdo, O. V. Covalent Linking Greatly Enhances Photoinduced Electron Transfer in Fullerene-Quantum Dot Nanocomposites: Time-Domain Ab Initio Study. J. Phys. Chem. Lett. 2012, 4, 1-6. (45)Long, R.; Prezhdo, O. V.; Fang, W. Nonadiabatic Charge Dynamics in Novel Solar Cell Materials. WIREs Comput. Mol. Sci. 2017, 7, e1305. (46)Wang, Y.; Fang, W.; Long, R.; Prezhdo, O. V. Symmetry Breaking at MAPbI3 Perovskite Grain Boundaries Suppresses Charge Recombination: Time-Domain Ab Initio Analysis. J. Phys. Chem. Lett. 2019, 10, 1617-1623. (47)Wang, Y.; He, J.; Yang, Y.; Zhang, Z.; Long, R. Chlorine Passivation of Grain Boundary Suppresses Electron-Hole Recombination in CsPbBr3 Perovskite by Nonadiabatic Molecular Dynamics Simulation. ACS Appl. Energy Mater. 2019, 2, 3419-3426. (48)He, J.; Fang, W.; Long, R.; Prezhdo, O. V. Superoxide/Peroxide Chemistry Extends Charge Carriers Lifetime but Undermines Chemical Stability of CH3NH3PbI3 Exposed to Oxygen: TimeDomain Ab Initio Analysis. J. Am. Chem. Soc. 2019, 141, 5798-5807. (49)Wang, S.; Luo, Q.; Fang, W.-H.; Long, R. Interfacial Engineering Determines Band Alignment and Steers Charge Separation and Recombination at an Inorganic Perovskite Quantum Dot/WS2 Junction: A Time Domain Ab Initio Study. J. Phys. Chem. Lett. 2019, 10, 1234-1241. (50)Qiao, L.; Sun, X.; Long, R. Mixed Cs and FA Cations Slow Electron-Hole Recombination in 26


Page 26 of 30

Page 27 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


FAPbI3 Perovskite by Time-Domain Ab Initio Study: Lattice Contraction versus Octahedral Tilting. J. Phys. Chem. Lett. 2019, 10, 672-678. (51)Kresse, G.; Furthmüller, J. Efficiency of Ab-Initio Total Energy Calculations for Metals and Semiconductors Using a Plane-Wave Basis Set. Comp. Mater. Sci. 1996, 6, 15-50. (52)Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for Ab Initio Total-Energy Calculations Using A Plane-Wave Basis Set. Phys. Rev. B 1996, 54, 11169. (53)Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865. (54)Blöchl, P. E. Projector Augmented-Wave Method. Phys. Rev. B 1994, 50, 17953. (55)Grimme, S. Semiempirical GGA-Type Density Functional Constructed with a Long-Range Dispersion Correction. J. Comput. Chem. 2006, 27, 1787-1799. (56)Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. A Consistent and Accurate Ab Initio Parametrization of Density Functional Dispersion Correction (DFT-D) for the 94 Elements H-Pu. J. Chem. Phys. 2010, 132, 154104. (57)Grimme, S.; Ehrlich, S.; Goerigk, L. Effect of the Damping Function in Dispersion Corrected Density Functional Theory. J. Comput. Chem. 2011, 32, 1456-1465. (58)He, J.; Vasenko, A. S.; Long, R.; Prezhdo, O. V. Halide Composition Controls Electron-Hole Recombination in Cesium-Lead Halide Perovskite Quantum Dots: A Time Domain Ab Initio Study. J. Phys. Chem. Lett. 2018, 9, 1872-1879. (59)Pan, J.; Quan, L. N.; Zhao, Y.; Peng, W.; Murali, B.; Sarmah, S. P.; Yuan, M.; Sinatra, L.; Alyami, N. M.; Liu, J.; et al. Highly Efficient Perovskite-Quantum-Dot Light-Emitting Diodes by Surface Engineering. Adv. Mater. 2016, 28, 8718-8725. (60)Ling, Y.; Tian, Y.; Wang, X.; Wang, J. C.; Knox, J. M.; Perez-Orive, F.; Du, Y.; Tan, L.; 27



Hanson, K.; Ma, B.; et al. Enhanced Optical and Electrical Properties of Polymer-Assisted AllInorganic Perovskites for Light-Emitting Diodes. Adv. Mater. 2016, 28, 8983-8989. (61)Yan, D.; Shi, T.; Zang, Z.; Zhou, T.; Liu, Z.; Zhang, Z.; Du, J.; Leng, Y.; Tang, X. Ultrastable CsPbBr3 Perovskite Quantum Dot and Their Enhanced Amplified Spontaneous Emission by Surface Ligand Modification. Small 2019, 15, 1901173. (62)Kilina, S.; Velizhanin, K. A.; Ivanov, S.; Prezhdo, O. V.; Tretiak, S. Surface Ligands Increase Photoexcitation Relaxation Rates in CdSe Quantum Dots. ACS Nano 2012, 6, 6515-6524. (63)Zhu, H.; Yang, Y.; Hyeon-Deuk, K.; Califano, M.; Song, N.; Wang, Y.; Zhang, W.; Prezhdo, O. V.; Lian, T. Auger-Assisted Electron Transfer from Photoexcited Semiconductor Quantum Dots. Nano Lett. 2014, 14, 1263-1269. (64)Long, R.; Prezhdo, O. V. Time-Domain Ab Initio Analysis of Excitation Dynamics in a Quantum Dot/Polymer Hybrid: Atomistic Description Rationalizes Experiment. Nano Lett. 2015, 15, 4274-4281. (65)Akbali, B.; Topcu, G.; Guner, T.; Ozcan, M.; Demir, M. M.; Sahin, H. CsPbBr3 Perovskites: Theoretical and Experimental Investigation on Water-Assisted Transition from Nanowire Formation to Degradation. Phy. Rev. Mater. 2018, 2, 034601. (66)Hedoux, A.; Le Bellac, D.; Guinet, Y.; Kiat, J.; Noiret, I.; Garnier, P. Raman Spectroscopy and X-ray Diffraction Studies on PbO and (PbO)1-x(TiO2)x. J. Phys.: Condens. Matter 1995, 7, 8547. (67)Burgio, L.; Clark, R. J.; Firth, S. Raman Spectroscopy as a Means for the Identification of Plattnerite (PbO2), of Lead Pigments and of Their Degradation Products. Analyst 2001, 126, 222227. (68)Nanda, K.; Sahu, S.; Soni, R.; Tripathy, S. Raman Spectroscopy of PbS Nanocrystalline 28


Page 28 of 30

Page 29 of 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Semiconductors. Phys. Rev. B 1998, 58, 15405. (69)Milekhin, A.; Sveshnikova, L.; Repinskii, S.; Gutakovskii, A.; Friedrich, M.; Zahn, D. Optical Vibration Modes in (Cd, Pb, Zn)S Quantum Dots in the Langmuir-Blodgett Matrix. Phys. Solid State 2002, 44, 1976-1980. (70)Akimov, A. V.; Prezhdo, O. V. Persistent Electronic Coherence Despite Rapid Loss of Electron-Nuclear Correlation. J. Phys. Chem. Lett. 2013, 4, 3857-3864. (71)Lax, M. The Franck-Condon Principle and Its Application to Crystals. J. Chem. Phys. 1952, 20, 1752-1760.

29



TOC Graphic

30


Page 30 of 30

Ultrafast Charge Separation and Recombination across a

Recommend Documents