Cl Vacancies Research Articles

Preparation of a novel iron oxychloride (FeOCl) auxiliary electrode in promoting electrokinetic remediation of Cr(VI) contaminated soil: An experimental and DFT calculation analysis.

The utilization of auxiliary electrode can improve substantially the electrokinetic remediation efficiency of heavy metal contaminated soil. The increase in the auxiliary electrode performance is the key to further promote the electrokinetic remediation efficiency. In this study, two kinds of auxiliary electrodes, pure FeOCl and doped FeOCl with W and S, were prepared and used in the electrokinetic remediation of Cr(VI) contaminated soil. The system equipped with the auxiliary electrode doped FeOCl brought more stable system current (202mA) and more uniform electric field than blank group (130mA). The reduction rate of Cr(VI) was increased by 50% due to the presence of Fe2+ and S2-. The accelerating migration of ions by auxiliary electrode was responsible for the improvement in electrokinetic remediation efficiency. Density functional theory (DFT) calculation showed that Cl vacancy formation energies of pure FeOCl, S-doped FeOCl (S/FeOCl) and W-doped FeOCl (W/FeOCl) were 1.29, 1.15 and 1.49eV respectively, and the ion diffusion barriers were 0.093, 0.099 and 0.148eV respectively. Calculation results indicated that the doping of S was conducive to the diffusion of Cl ions, and the bonding of W-Cl was stronger than Fe-Cl. The charging and discharging process of auxiliary electrode became easier due to the formation of lower vacancy in S-doped FeOCl, which could bring a higher current for the electrokinetic remediation system. The electrochemical performance of FeOCl doped with W and S was improved obviously. This study provided a further explanation for the positive role of auxiliary electrode in electrokinetic remediation system.

Multifunctional l-tryptophan derivative induced surface passivation for lateral perovskite photodetectors

Organic-inorganic hybrid perovskites have already been employed as promising light-sensitive materials for high-performance photodetectors (PDs) due to their intriguing optoelectronic features. Nonetheless, such perovskite-based PDs often suffer from low sensitivity, high dark current and inevitable degradation. In this work, a novel multifunctional molecule l-tryptophan ethyl ester hydrochloride (l-TEEH) was used to treat the surface defects of triple-cation mixed halide perovskite film. It is found that the modulator with multiple functional groups can effectively passivate the uncoordinated ions (Pb2+ and I-) and halide (I and Cl) vacancies of the perovskite film. Owing to the reduced defects, the dark current of the pristine perovskite PD significantly decreases from ∼ 10-9 A to ∼ 10-11 A after the l-TEEH treatment. Moreover, the perovskite PD with the l-TEEH treatment exhibits a large photoresponsivity (1.27 A/W) and an ultrahigh on/off ratio (∼9 × 103). More impressively, the optimized device shows excellent stability in air with a relative humidity of 40–50 %. Furthermore, the reliable imaging capability of perovskite device with the l-TEEH treatment is also successfully demonstrated.

Synchrotron radiation photoemission spectroscopy of the oxygen modified CrCl3 surface.

We investigate the experimentally challenging CrCl3 surface by photon energy dependent photoemission (PE). The core and valence electrons after cleavage of a single crystal, either in a ultra-high vacuum (UHV) or in air, are studied by keeping the samples at 150 °C, aiming at confirming the atomic composition with respect to the expected bulk atomic structure. A common spectroscopic denominator revealed by data is the presence of a stable, but only partially ordered Cl-O-Cr surface. The electronic core levels (Cl 2p, Cr 2p and 3p), the latter ones of cumbersome component determination, allowed us to quantify the electron charge transfer to the Cr atom as a net result of this modification and the increased exchange interaction between metal and ligand atoms. In particular, the analysis of multiplet components by the CMT4XPS code evidenced the charge transfer to be favored, and similarly the reduced crystal field due to the established polarization field. Though it is often claimed that a significant amount of Cl and Cr atomic vacancies has to be included, such a possibility can be excluded on the basis of the sign and the importance of the shift in the binding energy of core level electrons. The present methodological approach can be of great impact to quantify the structure of ordered sub-oxide phases occurring in mono or bi-layer Cr trihalides.

Mixed halide perovskite nanocrystals with surface engineering based on pseudohalide passivation and Short-Chain ligand exchange for High-Performance blue Light-Emitting diodes

Perovskite nanocrystals (PeNCs) have attracted considerable interest in light-emitting diodes (LEDs) owing to their unique optoelectronic properties. Although significant progress has been made in green and red perovskite LEDs (PeLEDs) with PeNCs, the performance of blue PeLEDs is still limited. The main obstacles for blue PeLEDs based on PeNCs are their Cl vacancy-induced low quantum efficiency in mixed halide (Br/Cl) systems and high electrical resistance from long organic capping ligands. In this study, to overcome these issues and achieve high-performance blue PeLEDs, a surface engineering (SE) strategy based on pseudohalide defect passivation and short-chain ligand exchange was introduced. By passivating Cl vacancies with SCN– and exchanging long-chain oleic acid and oleylamine ligands with short octylphosphonic acid and 3,3-diphenylpropyl amine, respectively, the optoelectronic properties of the PeNCs were significantly enhanced. The blue PeLEDs based on PeNCs, using SE, exhibited a maximum luminance of 1874 cd/m2 and maximum external quantum efficiency of 4.9 % at an electroluminescence wavelength of 467 nm, which satisfies the blue primary color requirement (467 nm) in Rec. 2020 color space.

Highly Efficient and Ultralong Afterglow Emission with Anti-Thermal Quenching from CsCdCl3 : Mn Perovskite Single Crystals.

Triplet exciton-based long-lived phosphorescence is severely limited by the thermal quenching at high temperature. Herein, we propose a novel strategy based on the energy transfer from triplet self-trapped excitons to Mn2+ dopants in solution-processed perovskite CsCdCl3 . It is found the Mn2+ doped hexagonal phase CsCdCl3 could simultaneously exhibit high emission efficiency (81.5 %) and long afterglow duration time (150 s). Besides, the afterglow emission exhibits anti-thermal quenching from 300 to 400 K. In-depth charge-carrier dynamics studies and density functional theory (DFT) calculation provide unambiguous evidence that carrier detrapping from trap states (mainly induced by Cl vacancy) to localized emission centers ([MnCl6 ]4- ) is responsible for the afterglow emission with anti-thermal quenching. Enlightened by the present results, we demonstrate the application of the developed materials for optical storage and logic operation applications.

Highly Efficient and Ultralong Afterglow Emission with Anti‐Thermal Quenching from CsCdCl3 : Mn Perovskite Single Crystals

AbstractTriplet exciton‐based long‐lived phosphorescence is severely limited by the thermal quenching at high temperature. Herein, we propose a novel strategy based on the energy transfer from triplet self‐trapped excitons to Mn2+ dopants in solution‐processed perovskite CsCdCl3. It is found the Mn2+ doped hexagonal phase CsCdCl3 could simultaneously exhibit high emission efficiency (81.5 %) and long afterglow duration time (150 s). Besides, the afterglow emission exhibits anti‐thermal quenching from 300 to 400 K. In‐depth charge‐carrier dynamics studies and density functional theory (DFT) calculation provide unambiguous evidence that carrier detrapping from trap states (mainly induced by Cl vacancy) to localized emission centers ([MnCl6]4−) is responsible for the afterglow emission with anti‐thermal quenching. Enlightened by the present results, we demonstrate the application of the developed materials for optical storage and logic operation applications.

Theoretical Understanding of thermoelectric energy conversion efficiency in Lead-Free halide double perovskites showing intrinsic defect tolerance

Thermoelectric devices based on the Seebeck effect can directly convert waste heat to electricity, but the demand for better thermoelectric materials remains unfulfilled. The lead-free halide double perovskites have recently shown promises for their stability and environment-friendly nature, but impacts from intrinsic defects (vacancies and anti-sites) on their thermoelectric performance remains elusive. Combing first-principle calculations, the Boltzmann transport theory, and the defect formation theory, we investigate the thermoelectric properties of lead-free double perovskite Cs2NaInCl6, taking the intrinsic defects into consideration. Our results demonstrate that the pristine Cs2NaInCl6 presents thermodynamic, mechanical, and dynamic stability. The band edges are mainly comprised of the electrons from In and Cl atoms. Furthermore, the double perovskite has an ultra-low lattice thermal conductivity and a high Seebeck coefficient, while showing a small charge carrier relaxation time and electric conductivity. Promisingly, the maximum ZT values can reach as high as ∼ 1.36 and ∼ 1.44 at 800 K temperature, respectively, with optimal extrinsic carrier concentrations of ∼ 1.9 × 1019 and 5.8 × 1020 cm−3 for N- and P-type carriers (holes and electrons), and the maximum power generation efficiency can reach ∼ 14% (for P-type) when the hot-side temperature is 800 K. Among various intrinsic defect types, we determine the preferable defect types in Cs2NaInCl6 based on the minimal defect formation energy criteria. The free carriers can be switched from N- to P-type under these two preferable defects, respectively, with Cl and Na vacancies. Even under a very high defect concentration of 2.1 × 1019/cm3 considered here, the extra carrier concentrations induced by the defects are only ∼ 1017 cm−3 at 800 K, showing strong defect tolerance in carrier concentration. This work suggests that lead-free halide double perovskites are promising thermoelectric materials, and they show strong intrinsic defect tolerance that prevents a negative impact on the extrinsic doping-controlled carrier concentrations.

Vacancy diffusion on a brominated Si(100) surface: Critical effect of the dangling bond charge state.

Silicon dangling bonds (DBs) on an adsorbate-covered Si(100) surface can be created in a scanning tunneling microscope (STM) with high precision required for a number of applications. However, vacancies containing DBs can diffuse, disrupting precisely created structures. In this work, we study the diffusion of Br vacancies on a Si(100)-2 × 1-Br surface in an STM under typical imaging conditions. In agreement with previous work, Br vacancies diffuse at a positive sample bias voltage. Here, we demonstrated that only vacancies containing a positively charged DB hop across the two atoms of a single Si dimer, while vacancies containing neutral and negatively charged DBs do not. Calculations based on density functional theory confirmed that positively charged Br (and Cl) vacancies have a minimum activation barrier. We propose that diffusion operates by both one-electron and two-electron mechanisms depending on the applied voltage. Our results show that the DB charge has a critical effect on the vacancy diffusion. This effect should be taken into account when imaging surface structures with charged DBs as well as when studying the diffusion of other atoms and molecules on the Si(100) surface with vacancies in an adsorbate layer.

Filling Chlorine Vacancy with Bromine: A Two-Step Hot-Injection Approach Achieving Defect-Free Hybrid Halogen Perovskite Nanocrystals.

Mixed-halide (Cl and Br) perovskite nanocrystals (NCs) are of particular interest because they hold great potential for use in high-efficiency blue light-emitting diodes (LEDs). Generally, mixed-halide compounds are obtained by either a one-step synthesis with simultaneous addition of both halide precursors or a postsynthetic anion exchange using the opposite halogen. However, both strategies fail to prevent the formation of deep-level Cl vacancy defects, rendering the photoluminescence quantum yields (PLQYs) typically lower than 30%. Here, by optimizing both thermodynamic and kinetic processes, we devise a two-step hot-injection approach, which simultaneously realizes Cl vacancy filling and efficient anion exchange between Cl- and Br-. Both the identity of Br precursors and their injection temperature are revealed to be critical in transforming those highly defective CsPbCl3 NCs to defect-free CsPb(Cl/Br)3. The optimally synthesized NCs exhibit a saturated blue emission at ∼460 nm with a near-unity PLQY and a narrow emission bandwidth of 18 nm, which represents one of the most efficient blue emitters reported so far. The turn-on voltage of the ensuing LEDs is ∼4.0 V, which is lower than those of most other mixed-halide perovskites. In addition, LEDs exhibit a stable electroluminescence peak at 460 nm under a high bias voltage of 8.0 V. We anticipate that our findings will provide new insights into the materials design strategies for producing high-optoelectronic-quality Cl-containing perovskites.

Glassy thermal conductivity in Cs3Bi2I6Cl3 single crystal

As the periodic atomic arrangement of a crystal is made to a disorder or glassy-amorphous system by destroying the long-range order, lattice thermal conductivity, κL, decreases, and its fundamental characteristics changes. The realization of ultralow and unusual glass-like κL in a crystalline material is challenging but crucial to many applications like thermoelectrics and thermal barrier coatings. Herein, we demonstrate an ultralow (~0.20 W/m·K at room temperature) and glass-like temperature dependence (2–400 K) of κL in a single crystal of layered halide perovskite, Cs3Bi2I6Cl3. Acoustic phonons with low cut-off frequency (20 cm−1) are responsible for the low sound velocity in Cs3Bi2I6Cl3 and make the structure elastically soft. While a strong anharmonicity originates from the low energy and localized rattling-like vibration of Cs atoms, synchrotron X-ray pair-distribution function evidence a local structural distortion in the Bi-halide octahedra and Cl vacancy. The hierarchical chemical bonding and soft vibrations from selective sublattice leading to low κL is intriguing from lattice dynamical perspective as well as have potential applications.

Photoswitchable Chlorine Vacancies in Ultrathin Bi4O5Cl2 for Selective CO2 Photoreduction

CO2 photoreduction currently faces two challenges: low photoreduction efficiency and poor product selectivity. Ultrathin two-dimensional bismuth oxyhalide, with a large number of surface vacancies (active sites), is an ideal material for regulating CO2 photoconversion. However, surface vacancies in this catalyst are easily deactivated during the reaction. CO2 photoreduction relies on sufficient active sites; hence, we synthesized ultrathin Bi4O5Cl2 nanoplates via a water-assisted self-assembly process with sufficient photoswitchable surface Cl vacancies for solar-driven CO2-to-CO reduction. The surface Cl vacancies were generated under light irradiation and filled again with migrated Cl– under an O2 atmosphere after turning off the irradiation. These photoswitchable vacancies enabled Bi4O5Cl2 to produce 58.49 μmol g–1 CO after 4 h of irradiation with high stability and lowered the energy barriers of the rate-determining (CO2-to-COOH–) and selectivity-determining steps (COOH–-to-CO), enabling 100% product selectivity. The reversible, photoswitchable Cl vacancies have a higher potential as active sites for CO2 photoreduction than synthetically introduced static surface vacancies, which could provide a feasible strategy for the creation of highly dynamic, active-defective catalysts for solar-energy conversion.

Effect of chlorine vacancy on the electronic and optical properties of CsSnCl3 perovskites for optoelectronic applications

In this work, we use the density functional theory (DFT)-based first-principal calculations to simulate geometric structures, electronic properties, and molecular dynamics (MD) of all inorganic CsSnCl3 perovskites without and with containing a chlorine vacancy. Our results demonstrate that the introduction of a Cl vacancy induces trap state and narrows the bandgap. The overlap between trap state and conduction band minimum (CBM) is large due to their similar chemical nature. Besides, the introduction of a Cl vacancy perturbs the Sn-Cl lattice vibration and corresponding phonon modes. Defective perovskite shows higher absorption than pristine perovskite owing to the narrower band gap.

Unconventional ferrimagnetism and enhanced magnetic ordering temperature in monolayer CrCl3 by introducing O impurities and Cl vacancies

Among chromium trihalides, a specific group of layered van der Waals magnetic materials, chromium trichloride (CrCl3) is the only system relatively stable under ambient conditions. This is also observed in reduced dimensionality where the emergence of extrinsic long-range ordered oxidized and Cl-vacancy-defective CrCl3 phases is experimentally reported. In this work, the magnetic properties of such two-dimensional (2D) systems are studied using density functional theory (DFT) calculations, including the electron-electron (U) repulsion interactions, and Monte Carlo (MC) simulations. Once the Cl vacancies are introduced, the results indicate that the monolayer CrCl3 has a magnetic moment that is enhanced linearly (up to 3.14 µ B /Cr) in the (1%–10%) vacancy concentration range. This determines a strengthening of the ferromagnetic state and a two-fold increase of the Curie temperature (up to 146 K) as valuated from MC simulations. More interestingly, once oxygen extrinsic impurities are considered, the monolayer CrCl3 structure is hybridized forming a stable ordered phase (O–CrCl3) with oxygen atoms allocated on the Cr atomic layer in the center of the honeycomb ring formed by Cr atoms. The magnetic moments of the O–CrCl3 system are localized on both Cr and O atoms, with oxygen antiferromagnetically coupled to chromium, resulting in a 2D ferrimagnetic hexagonal lattice system with an average magnetic moment of 2.14 µ B /Cr and a high magnetic ordering temperature (110 K) predicted with DFT in the mean field approach.

Investigation of the effect of point defects on the Li-ion conductivity of Li3InCl6.

The effect of point defects on the performance of the Li3InCl6 solid electrolyte was investigated using first-principles simulations. The Li-ion conductivity of Li3InCl6 was improved by the presence of point defects, such as a 4g site occupation by In or a Cl vacancy. The diffusion of Li ions was activated by the movement of some Li ions to vacant sites in the In layer, and the point defects reduced the energy barrier of this step, resulting in an overall increase in Li-ion diffusivity. The underlying mechanism of this effect was examined in terms of the structural and chemical properties of Li-Cl and In-Cl bonds, which indicated the energy barrier was closely related to changes in the bond distance and covalent interaction between the migrating Li and nearby Cl ions and nonuniformity among In-Cl bonds. Thermodynamic analysis showed that defect formation was unfavorable during conventional high-temperature synthesis; therefore, it is suggested that heating is applied at low temperatures only as a supplementary process to modify the crystallinity after preparing defective Li3InCl6 crystals by mechanical or solution-based routes to practically implement the effect of point defects and improve the solid electrolyte performance of Li3InCl6.

Electron beam analysis induces Cl vacancy defects in a NaCl thin film

This work reports on the electron-induced modification of NaCl thin film grown on Ag(110). We show using low energy electron diffraction that electron beam bombardment leads to desorption and formation of Cl vacancy defects on NaCl surface. The topographic structure of these defects is studied using scanning tunneling microscopy (STM) showing the Cl defects as depressions on the NaCl surface. Most of the observed defects are mono-atomic vacancies and are located on flat NaCl terraces. Auger electron spectroscopy confirms the effect of electron exposure on NaCl thin films showing Cl atoms desorption from the surface. Using density functional theory taken into account the van der Waals dispersion interactions, we confirm the observed experimental STM measurements with STM simulation. Furthermore, comparing the adsorption of defect free NaCl and defective NaCl monolayer on Ag(110) surfaces, we found an increase of the adhesion energy and the charge transfer between the NaCl film and the substrate due to the Cl vacancy. In details, the adhesion energy increases between the NaCl film and the metallic Ag substrate from 30.4 meV Å−2 for the NaCl film without Cl vacancy and from 39.5 meV Å−2 for NaCl film with a single Cl vacancy. The charge transfer from the NaCl film to the Ag substrate is enhanced when the vacancy is created, from 0.63e− to 1.25e−.

Simultaneous Enhancement of Photoluminescence and Stability of CsPbCl3 Perovskite Enabled by Titanium Ion Dopant

The application of CsPbCl3 perovskite is limited by the low photoluminescence quantum yield (PLQY), weak luminescence, and unpromising stability. Doping impurity ions has been considered as an effective strategy to tune the optoelectronic performances of perovskite. In this work, heterovalent Ti3+ ions are successfully doped into CsPbCl3 nanocrystals. It is found that Ti3+ ion doping could effectively improve the photoluminescence (PL) performance of CsPbCl3 nanocrystals. Density functional theory (DFT) calculations reveal that Ti3+ ions could introduce more band-edge states around the conduction band minimum of CsPbCl3, which is conducive to release electrons into conduction band. Furthermore, Ti3+ ion doping could inhibit the Cl vacancy concentration in CsPbCl3 and prevent the in-gap state caused by Cl vacancy. Notably, the stability of CsPbCl3 perovskite is greatly improved through Ti3+ ion doping. This work provides a new perspective for improving the optoelectronic properties of all-inorganic perovskites through heterovalent metal ion doping.

Room-Temperature Ferroelectricity in 2D Metal-Tellurium-Oxyhalide Cd7Te7Cl8O17 via Selenium-Induced Selective-Bonding Growth.

Two-dimensional (2D) ferroelectric materials have attracted increasing interest due to meeting the requirements of integration, miniaturization, and multifunction of devices. However, the exploration of intrinsic 2D ferroelectric materials is still in the early stage, for which the related reports are still limited, especially fewer ones prepared by chemical vapor deposition (CVD). Here, the ultrathin metal-tellurium-oxyhalide Cd7Te7Cl8O17 (CTCO) flakes as thin as 3.8 nm are realized via the selenium-induced selective-bonding CVD method. The growth mechanism has been confirmed by experiments and theoretical calculations, which can be ascribed to the induction of selective bonding of a hydrogen atom in H2O molecules by the introduction of selenium, leading to the generation of strong oxidants. Excitingly, switchable out-of-plane ferroelectric polarization was observed in CTCO flakes down to 6 nm at room temperature, which may be caused by mobile Cl vacancies. This work has implications for the synthesis and applications of 2D ferroelectric materials.

Biased screening for multi-component materials with Structures of Alloy Generation And Recognition (SAGAR)

Exploring new materials has attracted more and more attention, due to the improvement of technology and industry. Theoretically, the first-principles calculations combined with global optimization have been applied to predicting the properties of materials accurately and accelerate the discovery of new materials. For certain multi-component materials, the atoms are nearly at the lattice sites and the material exploration can be enhanced with biased screening. Based on the space symmetry, the calculations of duplicate structures can be avoided, and the specified constraints are applied to filter the energetically unstable candidates out. To provide the reasonable candidates for the first-principles calculations, we have released a program of Structures of Alloy Generation And Recognition (SAGAR), which can be conveniently used through the website. Herein, we will present several examples to show that the biased screening is practical and efficient, determining structures with high stabilities and novel properties. We have studied the distribution of up to 50% Cl vacancy concentration in NaCl and revealed semiconductor–metal transition in the boron/nitrogen co-doped diamond. The ground state anti-ferrormagnetic configuration of VCl2 is determined, as well as the low-lying hydrogenated-C60 structures with high symmetry. Our results indicate that the biased screening with proper constraint will effectively enhance the material exploration.

Electronic and magnetic properties of single-layer FeCl2 with defects

The formation of lattice defects and their effect on the electronic properties of single-layer ${\mathrm{FeCl}}_{2}$ are investigated by means of first-principles calculations. Among the vacancy defects, namely mono-, di-, and three-Cl vacancies and mono-Fe vacancy, the formation of mono-Cl vacancy is the most preferable. Comparison of two different antisite defects reveals that the formation of the Fe-antisite defect is energetically preferable to the Cl-antisite defect. While a single Cl vacancy leads to a $1{\ensuremath{\mu}}_{B}$ decrease in the total magnetic moment of the host lattice, each Fe vacant site reduces the magnetic moment by $4{\ensuremath{\mu}}_{B}$. However, adsorption of an excess Cl atom on the surface changes the electronic structure to a ferromagnetic metal or to a ferromagnetic semiconductor depending on the adsorption site without changing the ferromagnetic state of the host lattice. Both Cl-antisite and Fe-antisite defected domains change the magnetic moment of the host lattice by $\ensuremath{-}1{\ensuremath{\mu}}_{B}$ and $+3{\ensuremath{\mu}}_{B}$, respectively. The electronic ground state of defected structures reveals that (i) single-layer ${\mathrm{FeCl}}_{2}$ exhibits half-metallicity under the formation of vacancy and Cl-antisite defects; (ii) ferromagnetic metallicity is obtained when a single Cl atom is adsorbed on upper-Cl and Fe sites, respectively; and (iii) ferromagnetic semiconducting behavior is found when a Cl atom is adsorbed on a lower-Cl site or a Fe-antisite defect is formed. Simulated scanning electron microscope images show that atomic-scale identification of defect types is possible from their electronic charge density. Further investigation of the periodically Fe-defected structures reveals that the formation of the single-layer ${\mathrm{FeCl}}_{3}$ phase, which is a dynamically stable antiferromagnetic semiconductor, is possible. Our comprehensive analysis on defects in single-layer ${\mathrm{FeCl}}_{2}$ will complement forthcoming experimental observations.

The n-type and p-type conductivity mechanisms of the bulk BiOCl photocatalyst from hybrid density functional theory calculations.

In this work, the n-type and p-type conductivity mechanisms of bulk BiOCl are systematically investigated using first-principles calculations. Under the O-rich growth conditions, BiOCl presents the intrinsic p-type conductivity, which primarily originates from the contributions of the antisite defects OCl. This is in excellent agreement with the observed p-type conductivity in BiOCl under high oxygen partial pressure or in oxygen-saturated solutions in experiments. While BiOCl displays the intrinsic n-type conductivity under the Bi-rich growth conditions, the vacancy defects VCl are responsible for the character. Nevertheless, the extrinsic means or effects could lead to the production and ionization of the O vacancies, which could contribute to the n-type conductivity in BiOCl. Therefore, the intrinsic n-type conductivity behavior reported in BiOCl in recent experiments is well explained. Under the Cl-rich growth conditions, the major donor defects VCl and the major acceptor defects VBi in BiOCl compensate each other, leading to an intrinsic insulator. However, it is shown that the usual unintentional H impurities HBi could form the p-type conductivity in BiOCl under Cl-rich growth conditions and enhance the p-type conductivity under O-rich growth conditions. This helps to understand the p-type conductivity behavior reported or mentioned in BiOCl in many experiments. At the same time, we found that Group II elements Ca and Sr are superior p-type doping elements for BiOCl under the Cl-rich and O-rich growth conditions. The defect physics in the bulk BiOCl photocatalyst is well understood. This work may inspire more magnificent studies on developing BiOCl-based photocatalysts.