Open Circuit Voltage Decay Measurements Research Articles

NiOx Passivation in Perovskite Solar Cells: From Surface Reactivity to Device Performance.

Nonstoichiometric nickel oxide (NiOx) is one of the very few metal oxides successfully used as hole extraction layer in p-i-n type perovskite solar cells (PSCs). Its favorable optoelectronic properties and facile large-scale preparation methods are potentially relevant for future commercialization of PSCs, though currently low operational stability of PSCs is reported when a NiOx hole extraction layer is used in direct contact with the perovskite absorber. Poorly understood degradation reactions at this interface are seen as cause for the inferior stability, and a variety of interface passivation approaches have been shown to be effective in improving the overall solar cell performance. To gain a better understanding of the processes happening at this interface, we systematically passivated specific defects on NiOx with three different categories of organic/inorganic compounds. The effects on NiOx and the perovskite (MAPbI3) deposited on top were investigated using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Here, we find that the perovskite's structural stability and film formation can be significantly affected by the passivation treatment of the NiOx surface. In combination with density functional theory (DFT) calculations, a likely origin of NiOx-perovskite degradation interactions is proposed. The surface passivated NiOx layers were incorporated into MAPbI3-based PSCs, and the influence on device performance and operational stability was investigated by current-voltage (J-V) characterization, impedance spectroscopy (IS), and open circuit voltage decay (OCVD) measurements. Interestingly, we find that a superior structural stability due to interface passivation must not relate to high operational stability. The discrepancy comes from the formation of excess ions at the interface, which negatively impacts all solar cell parameters.

A green approach to synthesis of Ag-doped CeO2 nanorods embedded reduced graphene oxide nanocomposite for excellent photocatalytic and antimicrobial activity

In this paper, the Ag-doped cerium oxide nanorods embedded reduced graphene oxide (Ag@CeO2/rGO) nanocomposite was synthesized via Punica Granatum peel extract for for photocatalytic degradation of methylene blue (MB) and 4-nitrophenol (4-NP). The microstructural results confirmed the successful decoration of Ag-doped CeO2 nanorods on rGO matrix. The photocatalytic properties, including photocatalytic degradation, charge transfer kinetics and photocurrent generation, are systematically investigated using electrochemical impedance spectroscopy (EIS), photocurrent transient response (PCTR) and open circuit voltage decay (OCVD). The results of photocatalytic dye degradation measurements indicated that Ag@CeO2/rGO nanocomposite is more effective than pristine CeO2 to degrade the MB dye, and the degradation rate reached 100 % in 60 min. The decomposition of MB with Ag@CeO2/rGO nanostructure followed first-order reaction kinetics with a reaction rate constant (Ka) of 0.0198 min−1. The EIS and OCVD measurements revealed that the Ag doping and incorporation of rGO could suppress the recombination probability in CeO2 by the separation of photo-generated electron–hole pairs, which leads to the enhanced photocurrent generation and photocatalytic activity. The photocurrent density of Ag@CeO2/rGO, CeO2/rGO and pristine CeO2 are 215, 167.4 and 98.8 mAcm−2, respectively.

New equations to calculate carrier recombination lifetime of silicon epitaxial layer, based on open circuit voltage decay method

Abstract New equations for recombination lifetime calculation based on the open circuit voltage decay (OCVD) method were proposed. The new equations can yield accurate recombination lifetime values of the i-layer of PiN diodes in which a silicon epitaxial layer is employed, by eliminating the effects of carrier diffusion into p+ and n+ layers from the i-layer of PiN diodes, carrier injection into the i-layers from the depletion layer of PiN diodes, and surface recombination on the side wall of PiN diodes. To verify the effectiveness of the new equations, OCVD measurements were performed by employing technology computer-aided design (TCAD) simulation and actual PiN diodes. Although the calculated values implied the effect of epitaxial layer thickness, they were consistent with the results obtained under assumed lifetime conditions for TCAD simulation, the theory of recombination lifetime, and results in other reports.

Dye-sensitized solar cells with aluminum-doped zinc oxide nanoparticles-loaded electrolyte: A breakthrough solution for recombination and hysteresis suppression

Dye-sensitized solar cells (DSCs) suffer from reduced power conversion efficiency due to electron recombination with triiodide (I3−) ions at the photoanode/electrolyte interface. Organic additives are conventionally used in electrolyte to reduce recombination and improve the efficiency of the device. These additives react covalently with iodine (I2) in the electrolyte, leading to a reduction in the concentration of I3− ions. Other inorganic oxides, such as silica (SiO2), titania (TiO2), and magnesia (MgO), have been shown to improve the efficiency of the solar cell. These oxides can adsorb heavy ions to some extent. In this study, we investigated aluminum-doped zinc oxide nanoparticles (AZO NPs) as an inorganic additive with ionic adsorption properties towards I− and I3− anions in the electrolyte. We confirmed the ionic adsorption of AZO NPs through zeta potential and electrochemical impedance measurements. We observed a significant decrease in recombination between photogenerated electrons and electrolyte ions after adding AZO NPs, which resulted in an increase in open circuit voltage (VOC) and fill factor (FF) values. Furthermore, the incorporation of AZO NPs reduced the compelled hysteresis caused by the mismatch in current density-voltage curves for the forward and reverse scan direction. Mott-Schottky analysis confirmed the increase in VOC due to the negative shift in the Fermi level of the TiO2 photoanode. Additionally, open circuit voltage decay measurements indicated a longer electron lifetime at the TiO2/electrolyte interface in AZO NPs loaded electrolyte. Our findings suggest that AZO NPs have potential as an effective inorganic additive for improving the performance of DSCs.

MITRAGYNA SPECIOSA DYE SENSITISER AS THE LIGHT-HARVESTING MOLECULES FOR DYE-SENSITISED SOLAR CELLS

In this study, natural dye sensitisers derived from ketum (Mitragyna speciosa-MS), spinach (Spinacia oleracea-SO), curry (Murraya koenigii-MK), papaya (Carica papaya-CP), and henna (Lawsonia inermis-LI) were investigated for dye-sensitised solar cells (DSSCs). Ultraviolet-Visible Spectroscopy (UV-Vis), Fourier Transform Infrared spectroscopy (FTIR), Open-Circuit Voltage Decay (OCVD) and Current to Voltage (I-V) were used to analyse the natural dye and the fabricated DSSC. It was observed that all dye solutions contain the majority of important functional groups of chlorophyll-based sensitisers, which is crucial for the dye-to-TiO2 (Titanium (II) Oxide) attachment, making them suitable sources of energy harvesting pigments. In this regard, the dye pH and chemical bonding of the respective dyes play a significant role that contribute to the overall performance of the DSSCs. It was discovered that a dye based on MK provided the best DSSC performance. This is because MK-based dye has higher content of functional groups, an optimal pH, and the slowest properties of back electron recombination among the OCVD measurements. Because of the combination of these properties, the open-circuit voltage (VOC), short-circuit current density (JSC), and power conversion efficiency (PCE) values have been determined to be 0.58 V, 2.48 mA/cm2, and 0.47%, respectively.

Effects of Recombination Order on Open-Circuit Voltage Decay Measurements of Organic and Perovskite Solar Cells

Non-geminate recombination, as one of the most relevant loss mechanisms in organic and perovskite solar cells, deserves special attention in research efforts to further increase device performance. It can be subdivided into first, second, and third order processes, which can be elucidated by the effects that they have on the time-dependent open-circuit voltage decay. In this study, analytical expressions for the open-circuit voltage decay exhibiting one of the aforementioned recombination mechanisms were derived. It was possible to support the analytical models with experimental examples of three different solar cells, each of them dominated either by first (PBDBT:CETIC-4F), second (PM6:Y6), or third (irradiated CH3NH3PbI3) order recombination. Furthermore, a simple approach to estimate the dominant recombination process was also introduced and tested on these examples. Moreover, limitations of the analytical models and the measurement technique itself were discussed.

OCVD Measurement of Ambipolar and Minority Carrier Lifetime in 4H-SiC Devices: Relevance of the Measurement Setup

The open-circuit voltage decay (OCVD) method is a well-known technique for conducting electrical measurements of carrier lifetime: the main advantages lie in the simple setup and the possibility of carrying out measurements in commercial devices without the need of removing the package, as for optical methods. Despite several researchers having reported carrier lifetimes measured by the OCVD method in different devices, there has been little discussion about the potential effect of the experimental setup on the obtained results. By comparing the outputs of the experimental measurements with those of numerical simulations, this study investigates the overlooked effect of the OCVD measurement setup on the former. Due to the growing importance of SiC-based devices, the analysis is applied to a 4H-SiC p-i-n diode. Two main points are addressed: 1) the effect of circuit setup on the ambipolar lifetime is discussed and a method, originally developed for improving the estimate of low-level carrier lifetime in OCVD measurements, is used to correct the measured lifetime for this influence; 2) the origin of the local minimum eventually appearing in the lifetime versus time curves is also investigated. It is found that the minimum can also be related to the time constant of the experimental setup, giving rise to doubts about the usual interpretation of this minimum as the minority carrier lifetime. A method is thus proposed to help discriminate between the two interpretations.

A novel H2O2photoelectrochemical sensor based on ternary RGO/Ag-TiO2 nanotube arrays nanocomposite

Ternary nanocomposite photoelectrodes composed of Ag nanoparticles, reduced graphene oxide (RGO), and TiO2 nanotube arrays (TNTs) were successfully designed and achieved by a combining technique of cyclic voltammetry and anodic oxidation. Herein, the obtained RGO/Ag-TNTs composites were employed for photoelectrochemical (PEC) monitoring platform of hydrogen peroxide (H2O2) for the first time. Compared to pure TNTs, Ag-TNTs, and RGO-TNTs, the ternary RGO/Ag-TNTs nanocomposites with appropriate loading amount of RGO and Ag show much higher PEC activity, which were contributed to the synergistic effect resulting from the effective incorporation of Ag nanoparticles and RGO onto the TNTs to accelerate the electron transfer, increase the charge carrier density and prolong the electron lifetime demonstrated by electrochemical impedance spectroscopy (EIS), Mott-Schottky (M-S) measurements and open circuit voltage decay (OCVD) measurement. Under the optimal experimental conditions, the as-prepared PEC sensors exhibited an extremely wide dynamic range from 10−7 nM to 10 mM, and in the range of 0.1–10 mM with higher sensitivity and a detection limit of 20 μM. Moreover, the PEC sensors displayed good reproducibility, long-term stability, and selectivity toward the determination of H2O2. These excellent results make the as-developed ternary RGO/Ag-TNTs nanocomposites a promising candidate in PEC detection H2O2.

Hybrid solar cells of Ru-based dye complexes as interfacial modification layers: Energy level alignment and photoelectric properties improvement

The chemical incompatibility at the organic-inorganic heterojunction interface in hybrid solar cells is a serious issue that cannot be ignored. In this work, four Ru-based dye complexes (D-series organic dyes) were employed for the interfacial properties modulation. The results showed that the introduction of organic molecules can not only improve the compatibility between the organic and inorganic materials, but also provide an appropriate energy levels alignment of the materials in the hybrid films. A notable power conversion efficiency of 2.91% was achieved. The intrinsic factors that affecting the cells performance were investigated by electrochemical impedance and open circuit voltage decay measurements.

Effect of auxiliary acceptor on D-π-A based porphyrin sensitizers for dye sensitized solar cells

Among the tetrapyrrolic class of compounds, porphyrin based sensitizers have attracted considerable attention due to their excellent performance in dye-sensitized solar cells (DSSCs). Herein, two new donor-[Formula: see text]-acceptor (D-[Formula: see text]-A) concept based porphyrin sensitizers having donor 3-ethynylphenothiazine tethered at meso- position, zinc porphyrin as [Formula: see text]-spacer and acceptor either 3-(4-(benzo[c][1,2,5]thiadiazol-4-yl)phenyl)-2-cyanoacrylic acid (LG22), and 3-(4-(benzo[c][1,2,5]thiadiazol-4-yl)thiophene-2-yl)-2-cyanoacrylicacid (LG23) were designed and synthesized. Both sensitizers were characterized by various spectroscopic techniques and electrochemical methods. Optical, electrochemical and optimized studies suggest that these dyes are suitable for sensitization of nanocrystalline TiO2. The optimized device studies showed the power conversion efficiencies (PCE) of 1.86% and 1.37% for LG22 and LG23 dyes, respectively using [Formula: see text]/[Formula: see text] liquid redox shuttle. Finally, Charge Extraction (CE), Intensity Modulated Photovoltage Spectroscopy (IMVS), Intensity Modulated Photocurrent Spectroscopy (IMPS) and Open Circuit Voltage Decay (OCVD) measurements were adopted to understand in detail the electron transfer properties at various interfaces in a way to understand the performance limiting processes in these novel porphyrin sensitizers.

Radiation Resistance of High-Voltage Silicon and 4H-SiC Power p-i-n Diodes

The different effect of displacement damage produced by neutron irradiation on the static characteristics of 4.5-kV silicon and 4H silicon carbide (SiC) p-i-n power diodes is explained using deep level transient spectroscopy (DLTS), ${C}$ – ${V}$ profiling, and open-circuit voltage decay (OCVD) measurements. The number of introduced defects in SiC is higher, also the degradation of carrier lifetime and carrier removal proceeds more swiftly in SiC than those in silicon. However, smaller dimensions and a higher doping level of the n-base of the SiC diode compensate for these negative effects. As a result, the SiC p-i-n diode exhibits substantially higher resistance to neutron irradiation at higher fluences when the diode loses its ON-state carrier modulation capability. SiC also shows a negligible effect of irradiation on leakage current due to the wider bandgap. One may assume a better reliability of SiC bipolar devices over the silicon in a high neutron radiation environment.

The effect of inner-sphere reorganization on charge separated state lifetimes at sensitized TiO2 interfaces.

Improving the efficiency of photo-electrocatalytic cells depends on controlling the rates of interfacial electron transfer to promote the formation of long-lived charge separated states. Ultimately, for efficient catalytic assemblies to see widespread implementation, repeated electron transfer in the absence of charge recombination needs to be realized. In this study, a series of manganese-based transition metal complexes known to undergo charge transfer-induced spin crossover are employed to study how significant increases in inner-sphere reorganization energy affect the rates of interfacial electron transfer. Each complex is characterized by transient spectroscopic and electrochemical methods to calculate the rate of electron transfer to a model chromophore anchored to the surface of a TiO2 film. Likewise, open-circuit voltage decay measurements were used to determine the voltage-dependent lifetime of injected electrons in TiO2 in the presence of each complex. To further characterize the rates of electronic recombination, density functional theory was used to calculate the inner-sphere and outer-sphere reorganization energy for each complex. These calculations were then combined with classical Marcus theory to determine the theoretical rate of back-electron transfer from the TiO2 conduction band. These results show that, in model complexes, a significant reduction in the recombination rate constant is achieved for complexes possessing a significant inner-sphere reorganization energy.

The origin of enhanced photoelectrochemical activity in metal-ion-doped ZnO/CdS quantum dots

To improve the performance of photoelectrochemical cells, various metal ions have been incorporated into different host semiconductor nanocrystals. However, such an approach raises two new questions that must be answered to design and optimize this new doping strategy: (i) How do we accurately evaluate and rank these dopants? and (ii) how do the dopant-related midgap states tailor the band structure of the host semiconductors and the dynamics of the photogenerated carriers? In the present work, we use nanosheet-nanorod ZnO as a free-standing substrate and CdS as a host for indium, copper, manganese, and cerium doping. Given the uniform physical properties and electronic structure of this environment, the photocurrent density and photoelectrochemical efficiency increase from ZnO–CdS (3.0 mA/cm2, 0.41%), ZnO–CdS–In (4.4 mA/cm2, 0.59%), ZnO–CdS–Cu (5.1 mA/cm2, 0.98%), ZnO–CdS–Mn (6.7 mA/cm2, 1.07%), to ZnO–CdS–Ce (8.9 mA/cm2, 1.9%). With the help of electrochemical cyclic voltammetry, open-circuit voltage-decay measurements, and fluorescence spectroscopy, the band edges tailored by the midgap states and the carrier dynamics are clearly determined. Furthermore, a complex relationship between these properties and the material performance is established for accurately deciphering the photoelectrochemical activity. By monitoring the ·OH concentration during irradiation, the dynamic photoelectrochemical catalytic activity is also clearly depicted by using ZnO–CdS–Mn and ZnO–CdS–Ce as model photocatalysts.

Vertically aligned TiO2/ZnO nanotube arrays prepared by atomic layer deposition for photovoltaic applications

Vertically aligned TiO2/ZnO nanotube (NT) arrays were developed for application to photoanodes in mesoscopic solar cells. By a two-step anodic oxidation, vertically aligned TiO2 NT arrays with highly ordered surface structure were prepared, followed by deposition of a ZnO shell with a precisely controlled thickness using atomic layer deposition (ALD). When applied to a photoanode of dye-sensitized solar cells (DSSCs), the photovoltage is gradually enhanced as the ZnO shell thickness of the TiO2/ZnO NT electrodes is increased. Furtheremore, the electron lifetime in photoanodes is significantly enhanced due to the ZnO shell, which is examined by open-circuit voltage decay (OCVD) measurement. Photocurrent density-voltage (J-V) curves under the dark condition and OCVD spectra reveal that a negative shift in TiO2 conduction band potential and an energy barrier effect owing to the ZnO shell concurrently contribute to the enhancement of VOC and electron lifetime.

Ag-doped ZnO nanorods embedded reduced graphene oxide nanocomposite for photo-electrochemical applications.

In this paper, the Ag-doped zinc oxide nanorods embedded reduced graphene oxide (ZnO:Ag/rGO) nanocomposite was synthesized for photocatalytic degradation of methyl orange (MO) in the water. The microstructural results confirmed the successful decoration of Ag-doped ZnO nanorods on rGO matrix. The photocatalytic properties, including photocatalytic degradation, charge transfer kinetics and photocurrent generation, are systematically investigated using electrochemical impedance spectroscopy (EIS), photocurrent transient response (PCTR) and open circuit voltage decay (OCVD). The results of photocatalytic dye degradation measurements indicated that ZnO:Ag/rGO nanocomposite is more effective than pristine ZnO to degrade the MO dye, and the degradation rate reached 40.6% in 30 min. The decomposition of MO with ZnO:Ag/rGO nanostructure followed first-order reaction kinetics with a reaction rate constant (Ka) of 0.01746 min−1. The EIS, PCTR and OCVD measurements revealed that the Ag doping and incorporation of rGO could suppress the recombination probability in ZnO by the separation of photo-generated electron–hole pairs, which leads to the enhanced photocurrent generation and photocatalytic activity. The photocurrent density of ZnO:Ag/rGO, ZnO/rGO and pristine ZnO are 206, 121.4 and 88.8 nA cm−2, respectively.

Anchored Cu2O nanoparticles on graphene sheets as an inorganic hole transport layer for improvement in solar cell performance

We study the effect of dependent Cu2O nanoparticles (NPs) to the graphene oxide sheets (DCG), on the performance of dye-sensitized solar cells and the electron lifetime. Aqueous Cu2O nanoparticles were prepared and anchored on the graphene sheets by arc discharge method and then used as a coating layer to increase the electron lifetime in photoanode. Results show that open-circuit voltage of the cell increases up to 0.7V by use of DCG/TiO2 as a photoanode. In addition, performance characterization of the prepared cells by current density versus voltage (J–V) measurements show that the fill factor (FF) and power conversion efficiency (η) increase from η = 1.5% and FF = 52% for TiO2 photoanode (as a reference) to η = 3.48% and FF = 65% for DCG/TiO2 photoanode. The electron lifetime of the prepared samples was measured by open-circuit voltage-decay measurement (OCVD). Results show that the open circuit voltage and the electron–hole lifetime increase as well for TiO2 /DCG photoanode. To explore the effect of electron–hole concentration on the cell performance, we perturbed the electron–hole generation rate by three different illuminations and then measured the OCVD. Results show that the timescale of power decay for TiO2/DCG photoanode in high illumination is about 150 s.

Aggregation induced light harvesting of molecularly engineered D-A-π-A carbazole dyes for dye-sensitized solar cells

Novel class of metal free organic dyes (CCTh and CCBz) with D-A-π-A configuration, having carbazole as donor and 3-cyanopyridine as auxiliary acceptor replacing conventional benzannulated heterocycles along with variable π-linkers were synthesized and used in dye-sensitized solar cells (DSSCs). Both the dyes are having cyanoacrylic acid as the anchoring group with thiophene (CCTh) and phenylene (CCBz) as π-linkers. The photophysical, electrochemical, theoretical and photovoltaic properties of the dyes were investigated in detail. The absorption spectra of dyes on TiO2 showed broader absorption band for CCTh in comparison to the solution spectra indicating aggregation in solid state. The aggregation studies in varied THF/water fraction indicates J-aggregation for both the dyes. CCTh with thiophene linker showed broader absorption compared to CCBz, and the photovoltaic performance recorded for CCTh directly indicates better light harvesting ability corresponding to the red shifted J-aggregated states. Hence, solar cells fabricated with CCTh gave a power conversion efficiency of 3.39% and CCBz delivered an efficiency of 2.03% under full sun condition. A detailed investigation of device dynamics have been carried out employing charge extraction (CE), intensity-modulated photovoltage spectroscopy (IMVS) and open-circuit voltage decay (OCVD) measurements.

Influence of organic interface modification layer on the photoelectric properties of ZnO-based hybrid solar cells

The organic-inorganic heterojunction interface of hybrid solar cells plays an important role on the cell performance. The properties of heterojunction interface were modulated by employing two small organic molecules. The results showed that the introduction of organic molecules could improve the compatibility between the organic and inorganic materials, accelerate excitons separation efficiency and suppress carriers recombination. The power conversion efficiency of device was improved from 0.23% to 1.41%. Furthermore, the charge lifetime and interface charge transfer/recombination mechanisms were analyzed in detail. The intrinsic factors affecting the cell performance were investigated by electrochemical impedance and open circuit voltage decay measurements.

The photovoltaic performance of Ag2S quantum dots-sensitized solar cells using plasmonic Au nanoparticles/TiO2 working electrodes

The photovoltaic performance of silver sulfide (Ag2S) quantum dots-sensitized solar cells (QDSSCs) using different concentrations (0, 0.05, 0.1, 0.3 and 0.5 wt.%) of plasmonic Au nanoparticles (NPs)/titania (TiO2) electrodes has been investigated. Ag2S quantum dots (QDs) were adsorbed onto the Au NPs/titania electrodes using the successive ionic layer adsorption and reaction (SILAR) deposition technique. The morphological properties of the Au NPs and the prepared titania electrodes were characterized using transmission electron microscope (TEM) and scanning electron microscope (SEM), respectively. The energy-dispersive X-ray (EDX) spectra of the bare titania and Ag2S QDs-sensitized titania electrodes were recorded. The optical properties of the prepared Ag2S QDs-sensitized titania electrodes were measured using a UV–visible spectrophotometer. The estimated energy band gap of Ag2S QDs-sensitized titania electrodes is 1.96 eV. The photovoltaic performance of the assembled Ag2S QDSSCs was measured under 100 mW/cm2 solar illumination. The optimal photovoltaic parameters were obtained as follows: open circuit voltage [Formula: see text] = 0.50 V, current density [Formula: see text] = 3.18 mA/cm2, fill factor (FF) = 0.35 and energy conversion efficiency [Formula: see text] = 0.55% for 0.3 wt.% of Au NPs/titania electrode. These results are attributed to the enhancement in the absorption and decrease in the electron–hole pairs recombination rate. The open circuit voltage decay (OCVD) measurements of the assembled Ag2S QDSSCs were measured. The calculated electron lifetime [Formula: see text] in Ag2S QDSSCs with Au NPs/titania electrodes is at least one order of magnitude more than that with bare titania electrode. The cut-on–cut-off cycles of the solar illumination measurements show the rapid sensitivity and good reproducibility of the assembled Ag2S QDSSCs.

Activating BaTaO2N by Ca modifications and cobalt oxide for visible light photocatalytic water oxidation reactions

Despite a strong visible light absorbance as far as 660 nm, BaTaO2N generally exhibits a poor photocatalytic activity for water splitting under ordinary conditions. High levels of defects as well as photocatalytic self-decomposition are likely the major causes for this incommensuration. In this work, we have modified BaTaO2N by introducing Ca to the structure, i.e. BaCax/3Ta1-x/3O2+yN1-y (0 ≤ x, y ≤ 1). A number of important properties such as band gap, defects levels and nitrogen content can be tuned by varying the amounts of Ca in the structure. In particular, defects such as Ta4+ species can be effectively suppressed by Ca incorporation. More importantly, photocatalytic activity for water oxidation has been significantly enhanced and stability against photocatalytic self-decomposition has also been largely improved in Ca modified BaTaO2N. An apparent quantum efficiency as high as ∼ 2.1% at 420 ± 20 nm has been achieved and stands as the highest AQE for BaTaO2N reported to date. Photoelectrochemical (PEC) analysis reveals a much higher photocurrent in Ca modified BaTaO2N and identifies the role of cocatalyst CoOz in reducing charge transfer resistance for water oxidation reactions. Open-circuit voltage decay (OCVD) measurements further confirm the improved charge separation conditions in Ca modified BaTaO2N and functions of cocatalyst CoOz in collecting and storing photo-generated holes. The optimal loading point for cocatalyst CoOz corresponds to the one that gives the highest capacity for hole storage.