Phonon Bottleneck Research Articles

Reciprocating thermal behavior in the family of single ion magnets

Among the mononuclear transition metal and lanthanide complexes showing the slow magnetic relaxation, as a prerequisite of the single ion magnetism, there are examples of a non-traditional thermal behavior when at the low temperature the relaxation time, referring to the high-frequency relaxation channel, is shortened on further cooling instead of an expected prolongation. This reciprocating thermal behavior has been identified in a number of examples: for the Mn(II), Co(II), Ni(II), Cu(II), {Co(II)Co(III)}, {Gd(III)Ni(II)} and Dy(III) systems. The relaxation time in the low-temperature range can be recovered by applying equation τ–1 = CpbTl + FT–k where the phonon bottleneck process (rather than Raman process) and the “strange” process participate in the inverse relaxation time. The exponents of the temperature variable typically vary as l = 2–4 and k = 0.5–1.

Ultrafast intraband Auger process in self-doped colloidal quantum dots

Summary Investigating the separate dynamics of electrons and holes has been challenging, although it is critical for the fundamental understanding of semiconducting nanomaterials. n-Type self-doped colloidal quantum dots (CQDs) with excess electrons occupying the low-lying state in the conduction band (CB) have attracted a great deal of attention because of not only their potential applications to infrared optoelectronics but also their intrinsic system that offers a platform for investigating electron dynamics without elusive contributions from holes in the valence band. Here, we show an unprecedented ultrafast intraband Auger process, electron relaxation between spin-orbit coupling states, and exciton-to-ligand vibrational energy transfer process that all occur exclusively in the CB of the self-doped β-HgS CQDs. The electron dynamics obtained by femtosecond mid-infrared spectroscopy will pave the way for further understanding of the blinking phenomenon, disproportionate charging in light-emitting diodes, and hot electron dynamics in higher quantum states coupled to surface states of CQDs.

Spin blockade and phonon bottleneck for hot electron relaxation observed in n-doped colloidal quantum dots

Understanding and manipulating hot electron dynamics in semiconductors may enable disruptive energy conversion schemes. Hot electrons in bulk semiconductors usually relax via electron-phonon scattering on a sub-picosecond timescale. Quantum-confined semiconductors such as quantum dots offer a unique platform to prolong hot electron lifetime through their size-tunable electronic structures. Here, we study hot electron relaxation in electron-doped (n-doped) colloidal CdSe quantum dots. For lightly-doped dots we observe a slow 1Pe hot electron relaxation (~10 picosecond) resulting from a Pauli spin blockade of the preoccupying 1Se electron. For heavily-doped dots, a large number of electrons residing in the surface states introduce picosecond Auger recombination which annihilates the valance band hole, allowing us to observe 300-picosecond-long hot electrons as a manifestation of a phonon bottleneck effect. This brings the hot electron energy loss rate to a level of sub-meV per picosecond from a usual level of 1 eV per picosecond. These results offer exciting opportunities of hot electron harvesting by exploiting carrier-carrier, carrier-phonon and spin-spin interactions in doped quantum dots.

Investigation of Hot Carrier Cooling Dynamics in Monolayer MoS2

The hot carrier cooling dynamics in the C-excitonic state of monolayer MoS2 is slowed down by the hot phonon bottleneck and Auger heating effects, as exploited by ultrafast transient absorption spectroscopy. The hot carrier cooling process, determined by the hot phonon bottleneck, can be prolonged through rising the excitation photon energy or increasing the absorbed photon flux. By inducing the Auger heating effect under higher absorbed photon flux, the hot carrier lifetime also increases at the low excitation photon energy. When these two effects are combined under higher excitation photon energy and higher absorbed photon flux, the hot phonon bottleneck is gradually weakened because of Auger recombination. In addition, the similar hot carrier phenomenon can be observed in A/B excitonic states owing to the same physical mechanism. Our work establishes a solid photophysics foundation for 2D transition-metal dichalcogenide applications in advanced energy conversion, optical quantum communication, quantum technology, etc.

A multifunctional magnetic material based on a solid solution of Fe(ii)/Co(ii) complexes with a macrocyclic cyclam-based ligand.

In order to prepare a multifunctional magnetic material combining spin crossover together with single-molecular magnetism, co-crystallization of Fe(ii) and Co(ii) complexes of the pyridine derivative of cyclam (Py2-C = 1,8-bis(pyridin-2-ylmethyl)-1,4,8,11-tetraazacyclotetradecane) was performed. Complexes with the general formula [MII(Py2-C)](ClO4)2·H2O (MII = Fe (1), Co (2) or Fe0.4Co0.6 (3)) were prepared and thoroughly characterized. Based on X-ray molecular structures, they formed octahedral complexes with cis-arrangement of the coordinated pyridine moieties. Magnetic data revealed that the Fe(ii) complex 1 shows complete SCO with the transition temperature T1/2 = 141 K, which is preserved also in the mixed Fe/Co system 3 (T1/2 = 128 K). Co(ii) complex 2 behaves as a field-induced single-molecule magnet as well as the mixed system 3 with a direct and phonon bottleneck relaxation process, respectively. This is the first example of such Fe/Co solid solution providing SCO in combination with field-induced SMM properties. Unfortunately, the light-induced excited spin-state trapping (LIESST) effect was not observed either for the Fe(ii) complex 1 or the mixed system 3 and thus, the effect of SCO on SMM properties at low temperature could not be investigated in detail. Nevertheless, the obtained results clearly document the success of the solid solution methodology for the preparation of multifunctional magnetic materials.

Hot carriers in mixed Pb-Sn halide perovskite semiconductors cool slowly while retaining their electrical mobility

The electron-phonon interaction controls the intrinsic mobility of charges in metal halide perovskites, and determines the rate at which carriers lose energy. Here, the carrier mobility and cooling dynamics were directly examined using a combination of ultrafast transient absorption spectroscopy and optical pump, THz probe spectroscopy, in perovskites with different lead and tin content, and for a range of carrier densities. Significantly, the carrier mobility in the ``hot phonon bottleneck'' regime, where the LO phonon bath keeps carriers warm, was found to be similar to the mobility of cold carriers. A model was developed that provides a quantitative description of the experimental carrier cooling dynamics, including electron-phonon coupling, phonon-phonon coupling and the Auger mechanism. In the Pb and Sn alloy the duration of the hot carrier regime was extended as a result of the slower decay of optical phonons. The findings offer an intuitive link between macroscopic properties and the underlying microscopic energy transfer processes, and suggest new routes to control the carrier cooling process in metal halide perovskites to optimize optoelectronic devices.

Size-Dependent Hot Carrier Dynamics in Perovskite Nanocrystals Revealed by Two-Dimensional Electronic Spectroscopy.

The lifetimes of hot carriers have been predicted to be prolonged in small nanocrystals with an inter-level spacing larger than phonon energy. Nevertheless, whether such a phonon bottleneck is present in perovskite semiconductor nanocrystals remains highly controversial. Here we report compelling evidence of a phonon bottleneck in CsPbI3 nanocrystals with marked size-dependent relaxation of hot carriers by using broadband two-dimensional electronic spectroscopy (2DES). By combining high resolutions in both the time (<10 fs) and excitation energy domains, 2DES allows the clear disentanglement of the thermalization and cooling processes. The lifetime is over doubled for hot carriers when the average edge length of the nanocrystals decreases from 8.2 nm down to 4.6 nm. The confirmation of the phonon bottleneck effect suggests the feasibility of controlling hot carrier dynamics in perovskite semiconductors with nanocrystal size for potential applications of hot carrier devices.

Modeling Auger Processes with Nonadiabatic Molecular Dynamics.

Auger-type energy exchange plays key roles in the carrier dynamics in nanomaterials due to strong carrier-carrier interactions. However, theoretical descriptions are limited to perturbative calculations of scattering rates on static structures. We develop an accurate and efficient ab initio technique to model Auger scattering with nonadiabatic molecular dynamics. We incorporate the many-body Coulomb matrix into several surface hopping methods and describe simultaneously charge-charge and charge-phonon scattering in the time-domain and in a nonperturbative, configuration-dependent manner. The approach is illustrated with a CdSe quantum dot. Auger scattering between electrons and holes breaks the phonon bottleneck to electron relaxation. The bottleneck is recovered when electrons and holes are decoupled. The simulations correctly reproduce all experimental processes and time scales, including Auger- and phonon-assisted cooling of hot electrons, intraband carrier relaxation, and carrier recombination. Providing detailed insights into the energy flow, the developed method allows studies of carrier dynamics in nanomaterials with strong carrier-carrier interactions.

Manipulation of Molecular Qubits by Isotope Effect on Spin Dynamics

Controlling spin behavior via external stimuli is a key route to develop molecular spintronics devices. Photons, temperature, pressure, chemicals, and electric field are the possible stimuli. Herei...

Ab initio study of electron and phonon coupling in silicon

We have studied electron-phonon coupling in silicon and its relation to hot carriers thermalization. The calculation of electron-phonon and phonon-electron interactions in silicon was obtained from first-principles density functional theory and many-body perturbation theory. Electron and phonon relaxation times were calculated subsequently. Moreover, the results showed that silicon exhibits a relatively wide phononic band gap along the symmetry line X-W, which prevents the Klemens mechanism leading to a phonon bottleneck effect. As demonstrated, phonon-electron interactions can play an important role in mitigating the electron thermalization along this symmetry line. This work shade light on the importance of including the phonon- electron interactions in the ab initio approach for future semiconductor materials engineering.

Charge Carrier Relaxation in Colloidal FAPbI3 Nanostructures Using Global Analysis

We study the hot charge carrier relaxation process in weakly confined hybrid lead iodide perovskite colloidal nanostructures, FAPbI3 (FA = formaminidium), using femtosecond transient absorption (TA). We compare the conventional analysis method based on the extraction of the carrier temperature (Tc) by fitting the high-energy tail of the band-edge bleach with a global analysis method modeling the continuous evolution of the spectral lineshape in time using a simple sequential kinetic model. This practical approach results in a more accurate way to determine the charge carrier relaxation dynamics. At high excitation fluence (density of charge carriers above 1018 cm−3), the cooling time increases up to almost 1 ps in thick nanoplates (NPs) and cubic nanocrystals (NCs), indicating the hot phonon bottleneck effect. Furthermore, Auger heating resulting from the multi-charge carrier recombination process slows down the relaxation even further to tens and hundreds of picoseconds. These two processes could only be well disentangled by analyzing simultaneously the spectral lineshape and amplitude evolution.

Electromagnetically induced transparency in a mono-isotopic 167Er:7LiYF4 crystal below 1 Kelvin: microwave photonics approach.

Electromagnetically induced transparency allows for the controllable change of absorption properties, which can be exploited in a number of applications including optical quantum memory. In this paper, we present a study of the electromagnetically induced transparency in a 167Er:7LiYF4 crystal at low magnetic fields and ultra-low temperatures. The experimental measurement scheme employs an optical vector network analysis that provides high precision measurement of amplitude, phase and group delay and paves the way towards full on-chip integration of optical quantum memory setups. We found that sub-Kelvin temperatures are the necessary requirement for observing electromagnetically induced transparency in this crystal at low fields. A good agreement between theory and experiment is achieved by taking into account the phonon bottleneck effect.

Decelerated Hot Carrier Cooling in Graphene via Nondissipative Carrier Injection from MoS2.

One key to improve the performance of advanced optoelectronic devices and energy harvesting in graphene is to understand the predominant carrier scattering via optical phonons. Nevertheless, low light absorbance in graphene yields a limited photoexcited carrier density, hampering the hot carrier effect, which is strongly correlated to the hot optical phonon bottleneck effect as the energy-loss channel. Here, by integrating graphene with monolayer MoS2 possessing stronger light absorbance, we demonstrate an efficient interfacial hot carrier transfer between graphene and MoS2 in their heterostructure with a prolonged relaxation time using broadband transient differential transmittance spectroscopy. We observe that the carrier relaxation time of graphene in the heterostructure is 4 times slower than that of bare graphene. This is explained by nondissipative interlayer transfer from MoS2 to graphene, which is attributed to the enhanced hot optical phonon bottleneck effect of graphene in the heterostructure by an increased photoexcited carrier population. A significant reduction of both amplitude and relaxation time in A- and B-excitons is another evidence of the interlayer transfer from MoS2 to graphene. The nondissipative interlayer charge transfer from MoS2 to graphene is confirmed by density functional calculations. This provides a different platform to further study the photoinduced hot carrier effect in graphene heterostructures for photothermoelectric detectors or hot carrier solar cells.

Energy Transport of Hybrid Charge-Transfer Excitons.

We investigate the energy transport in an organic-inorganic hybrid platform formed between semiconductors that support stable room-temperature excitons. We find that following photoexcitation, fast-moving hot hybrid charge-transfer excitons (HCTEs) are formed in about 36 ps via scattering with optical phonons at the interface between j-aggregates of organic dye and inorganic monolayer MoS2. Once the energy falls below the optical phonon energy, the excess kinetic energy is relaxed slowly via acoustic phonon scattering, resulting in energy transport that is dominated by fast-moving hot HCTEs that transition into cold HCTEs in about 110 ps. We model the exciton-phonon interactions using Fröhlich and deformation potential theory and attribute the prolonged transport of hot HCTEs to phonon bottleneck. We find that the measured diffusivity of HCTEs in both hot and cold regions of transport was higher than the diffusivity of MoS2 A exciton and verify these results by conducting the experiments with different excitation energies. This work not only provides significant insight into the initial energy transport of HCTEs at organic-inorganic hybrid interfaces but also contributes to the formulation of a complete physical picture of the energy dynamics in hybrid materials, which are poised to advance applications in energy conversion and optoelectronic devices.

Slow carrier cooling in methylammonium lead bromide quantum dots: Evidence of hot phonon bottleneck

Photoinduced charge carrier dynamics studies in lead halide perovskites helps in explaining key processes like carrier trapping, diffusion and multiexciton dynamics etc. which are of importance to understand the fate of excitons. In the present study, we investigate the dynamics in methylammonium lead bromide perovskite nanocrystals under low and high pump intensity to study hot carrier cooling mechanisms. The single exciton studies conducted under low pump fluences (<N> = 0.3) revealed slow carrier decay with a significant fraction of >1 ns decay times as expected due to long radiative carrier recombination times. This also indicated that fast carrier trapping does not occur as evidenced by absence of any fast decay components. The hot carrier (HC) cooling mechanisms were verified by studying carrier density dependence of carrier temperature decays as extracted from the higher energy part of exciton bleach. These studies revealed a very fast cooling of ∼150 fs under low carrier density 1.5 × 1017/ cm3. However additional experiments under higher carrier densities of ∼1018-1019/cm3 showed a very slow carrier temperature decay with decay time ∼100 ps for the highest intensity investigated. The analysis of hot carrier lifetimes revealed Auger heating and acoustic phonon up-conversion as reason for hot carrier relaxations at higher intensities. Additionally, we carried out experiments under hole quencher, we found lower initial carrier temperatures and faster decay indicating highly efficient hole transfer to the quencher in a time scale faster than cooling of carrier at higher intensities. These results hint at possibility of molecular design for enabling efficient hot carrier extraction from these Quantum Dots (QDs).

Coexistence of Spin-Lattice Relaxation and Phonon-Bottleneck Processes in GdIII -Phthlocyaninato Triple-Decker Complexes under Highly Diluted Conditions.

Gd3+ complexes have been shown to undergo unusual slow magnetic relaxation processes similar to those of single-molecule magnets (SMMs), even though Gd3+ does not exhibit strong magnetic anisotropy. To reveal the origin of the slow magnetic relaxation of Gd3+ complexes, we have investigated the magnetic properties and heat capacities of two Gd3+ -phthalocyaninato triple-decker complexes, one of which has intramolecular Gd3+ -Gd3+ interactions and the other does not. It was found that the Gd3+ -Gd3+ interactions accelerate the magnetic relaxation processes. In addition, magnetically diluted samples, prepared by doping a small amount of the Gd3+ complexes into a large amount of diamagnetic Y3+ complexes, underwent dual magnetic relaxation processes. A detailed dynamic magnetic analysis revealed that the coexistence of spin-lattice relaxation and phonon-bottleneck processes is the origin of the dual magnetic relaxation processes.

Harnessing Hot Phonon Bottleneck in Metal Halide Perovskite Nanocrystals via Interfacial Electron–Phonon Coupling

Slow hot carrier (HC) cooling resulting from hot phonon bottleneck has been widely demonstrated in metal halide perovskites. Although manipulating HC kinetics in these materials is of both fundamental and technological importance, this task remains a daunting challenge. Here, via interfacial engineering, i.e., epitaxial growth of Cs4PbBr6 on CsPbBr3 nanocrystals (NCs), we have revealed an obvious shortening of HC cooling times, evidenced by transient absorption and ultrafast PL spectra. Collaborated with the longitudinal optical (LO) phonon model, theoretical calculations verify the breaking of the hot phonon bottleneck in CsPbBr3@Cs4PbBr6 and identify the interfacial electron-LO phonon coupling as the leading mechanism for the observed large tuning of HC cooling times. Especially, the participation of LO phonons from Cs4PbBr6 enables the efficient Klemens channel for hot phonon decay. Our findings establish an effective method to tailor HC dynamics in perovskite NCs, which could be conducive to improving the performance of optoelectronic applications.

Long Carrier Diffusion Length and Slow Hot Carrier Cooling in Thin Film Mixed Halide Perovskite

The long diffusion length is the key to achieve remarkable power conversion efficiency and delayed hot carriers (HCs) relaxation helps to overcome the theoretical Shockley–Queisser limit in perovskite photovoltaic. Here, we investigate the incident photon density dependent bandedge bleaching and HCs dynamics in thin film methyl-ammonium lead iodide-chloride (mixed halide) perovskite using transient absorption spectroscopy. The bandedge bleaching dynamics shows the radiative recombination rate constant of the order of ∼10−11 cm−3 s−1 results in the maximum carrier diffusion length of the order of ∼10 μm. The HCs dynamics indicates cooling occurs by longitudinal-optical (LO) phonon emission in early ∼800 fs via Frohlich electron–phonon interaction at low-carrier concentration (∼1.7 × 1018 cm−3) and an efficient phonon bottleneck due to the delayed LO-phonon decay by two order of magnitude about ∼11 ± 1.3 ps at high carrier density (∼1019 cm−3). Our finding shows the potential of thin film mixed halide perovskite in HCs photovoltaic and light emission application.

(Invited) Colloidal Semiconductor Nanocrystals Under Intense Optical Excitations Towards Efficient Lasing and Hot-Carrier Harvesting

Colloidal semiconductor nanocrystals appeal to broad range of applications including bio-imaging and displays where essential optical properties such as photoluminescence quantum yields are typically characterized under weak optical excitation conditions producing less than one exciton per particle on average. On the other hand, applications such as lasing and high-brightness lighting require intense excitation conditions producing more than one exciton per nanocrystal on average. Unfortunately, prior reports showed that multiple excitons in these nanocrystals are annihilated at extremely high rates due to nonradiative Auger recombination. Therefore, energy of the multiple excitons is lost to heating before it can be used and converted into electrical or light energy.In the first of the talk, I will present a colloidal nanocrystal system, which provides remarkable performance in lasing applications. Recently, we showed that atomically-flat colloidal CdSe nanoplatelets exhibit record-high optical gain coefficients under intense optical excitation conditions [1]. In contrast, optical gain coefficients in conventional CdSe nanocrystals (e.g., core/shell quantum dots) saturate at very low excitation fluences; typically at a fluence that is two times the gain threshold. In the case of the CdSe nanoplatelets, optical gain saturates at an exceptionally high level which is an order of magnitude larger than those of prototypical nanocrystals. As a result, CdSe nanoplatelets attain giant modal gain coefficients which we directly measure to be on the order of 6000 cm-1 with the intrinsic material gain coefficients exceeding 15,000 cm-1. The measured modal gain in the nanoplatelets is the highest among any lasing media measured at room temperature to date. This indicates that nanoplatelets sustain optically excited multiple excitons and enable their strong contribution to the gain before the nonradiative Auger recombination kicks in. We hypothesize that multiexcitons in the nanoplatelets form highly stable biexcitonic species as claimed in epitaxial quantum wells at low temperatures before [2].In the second part of the talk, I will present a new technique to monitor how colloidal nanocrystals heat up at the nanoscale following an intense optical excitation, which is important for applications requiring intense excitation conditions. Previously, a phonon bottleneck effect between excited state electrons and optical phonons have been predicted but has never been observed experimentally [3]. This implied that nanocrystals should heat up rather quickly (sub-picosecond to picosecond timescale) by transferring the energy stored in the electronic system into the lattice via electron – phonon coupling. However, timescales of the heating up nanocrystals, which involve both electron – phonon and phonon – phonon couplings, could not be straightforwardly characterized with the existing time-resolved techniques. Here, we utilize ultrafast electron diffraction measurements, where we probe the lattice of the nanocrystals through following an optical pump. With this method, we resolve the intrinsic timescales of the heat transfer within the colloidal nanocrystals [4]. Distinct from previous optical studies, we observe highly slow heating up of the nanocrystals which strikingly depend on the excitations whether generated in the core or the shell of the nanocrystals.[1] B. Guzelturk et al. Nano Letters 19, 277 (2019)[2] D. A. B. Miller, “Optical physics of Quantum Wells”[3] R. Schaller et al. Phys. Rev. Lett. 95, 196401 (2005)[4] B. Guzelturk et al. (in-preparation)

(Invited) Hot Hole Transfer from Zn-Ag-in-Te Nanocrystals Photo-Excited with High-Energy Photons

Semiconductor nanocrystals (NCs), so-called quantum dots, exhibit unique size-dependent physicochemical properties different from bulk materials and have attracted intense attention for the application to solar light energy conversion systems. Since the relaxation rates of carriers in highly excited states are remarkably reduced by the discrete energy levels of semiconductor NCs due to the phonon bottleneck effect, unique photoresponses of semiconductor NCs are induced by the absorption of photons with energy higher than the energy gap (Eg) of NCs. For example, by extending the relaxation time of hot carriers, it was possible to transfer excess kinetic energy before releasing it as heat. Thus, next-generation solar cells of outstandingly high efficiency beyond the Shockley-Queisser limit can be developed if photogenerated carriers are harvested from a semiconductor NC without energy loss of incident photons.I-III-VI2 semiconductor-based nanoparticles, such as CuInS2 or AgInS2 and their solid solution with ZnS, have been intensively studied as a visible-light-driven photocatalyst because of their excellent optical properties (e.g. direct band gaps in the visible-light region, and large absorption coefficients). Recently, we prepared ZnTe-AgInTe2 solid solution ((AgIn)xZn2(1-x)Te2: ZAITe) NCs with a rod shape, the Eg of which was enlarged from 1.20 to 1.60 eV with an increase in Zn content.1 ZAITe NCs exhibited a narrow band-edge PL peak with high QYs, and the PL peak wavelength was tunable in the near-IR wavelength region depending on their energy gap (Eg). These NCs are expected to act as a photosensitizer for near-IR light, but their photoelectrochemical properties have not been investigated. In this study, we clarified the electronic energy structure of ZAITe NCs for utilization as a photosensitizer and then investigated the photoelectrochemical properties of ZAITe NC-immobilized photoelectrodes.2 Since photons in the visible light region have much larger energies than the Egs of ZAITe NCs, it is important to examine the influence of photogenerated carriers with excess energies on the photoelectrochemical properties of ZAITe NCs with the goal of application to photovoltaic devices.ZAITe NCs were synthesized by a thermal reaction of corresponding metal acetates and a Te precursor in 1-dodecanethiol at 180°C for 180 min. TEM observations revealed that rod-shaped NCs with width of ca. 4 nm and length of ca. 11 nm were formed regardless of chemical composition of particles, that is, the x value. We revealed the electronic energy structures of ZAITe NCs with the compositions of x= 1.0, 0.75, and 0.5, the Eg values of which were 1.20, 1.27, and 1.46 eV, respectively. The band-edge potentials of conduction band (ECB) and valence band (EVB) were negatively and positively shifted with an increase in the Eg of NCs, the degree being more remarkable for the change in ECB.The photocurrent-potential curves of ZAITe NCs-immobilized on ITO electrode with thickness of less than one monoparticle layer resembled a p-type semiconductor photoresponse, but the behavior was remarkably different from those of ZAITe NC multilayer films: The onset of cathodic photocurrent was shifted more positively than that of EVB of ZAITe NCs and the photocurrent generation efficiency was significantly enlarged, when photons of energy higher than ca. 2.5 eV were irradiated. The photocurrent onset potential was also dependent on the energy of irradiaited photons for thin ZAITe NC films. Irradiation of photons with lower energy than 2.43 eV gave the onset potential at around 0 V vs. Ag/AgCl, being comparable to the EVB of ZAITe NCs with x = 0.75, -0.05 V vs. Ag/AgCl. On the other hand, the increases of photon energy to 2.95 and 3.40 eV gave more positive onset potentials of 0.1 and 0.3 V vs. Ag/AgCl, respectively. Thus we conclude that the excitation with photons of > ca. 2.5 eV enabled the direct injection of hot holes from ZAITe NCs into ITO electrodes, resulting in enhancement of the photocurrent generetion efficiency of ZAITe NCs. Reference 1. T. Kameyama, et al., J. Mater. Chem. C, 2018, 6, 2034.2. T. Kameyama, et al., ChemNanoMat, 2019, 5, 1028.