Optimum Band Gap Research Articles

Bimetallic superalkali substitution in the CsPbBr3 perovskite: Pseudocubic phases and tunable bandgap.

Perovskites attract attention as efficient light absorbers for solar cells due to their high-power conversion efficiency (up to 24%). The high photoelectric conversion efficiency is greatly affected by a suitable band structure. Cation substitution can be an effective approach to tune the electronic band structure of lead halide perovskites. In this work, superalkali cations were introduced to replace the Cs+ cation in the CsPbBr3 material. The bimetallic superalkalis (LiMg, NaMg, LiCa, and NaCa) were inserted since they are structurally simple systems and have a strong tendency to lose one electron to achieve a closed-shell cation. The cation substitution in the lead halide perovskite leads to changes in the shape of both valence and conduction bands compared to CsPbBr3. Introducing superalkali cations produces extra electronic states close to the Fermi level, which arise from the formation of alkali earth metal states at the top of the valence band. Our first-principles computations reveal that bimetallic superalkali substitution decreases the bandgap of the perovskite. The bandgaps of MgLi-PbBr3 (1.35eV) and MgNa-PbBr3 (1.06eV) are lower than the bandgap of CsPbBr3 (2.48eV) and within the optimal bandgap (i.e., 1.1-1.4eV) for single-junction solar cells. Thus, the MgLi-PbBr3 and MgNa-PbBr3 inorganic perovskites are promising candidates for high-efficiency solar cells.

Advances in low-cost and nontoxic materials based solar cell devices

Photovoltaics (PV) have become increasingly popular and reached as the third-largest renewable energy source. Thin-film solar cells made from earth-abundant, inexpensive and environmentally friendly materials are needed to replace the current PV technologies whose large-scale applications are limited by material and/or resource constraints. Near optimum direct optical bandgap of 1.3 eV, high absorption coefficient (>104 cm−1), less toxic, and abundant raw resources along with considerable scalability have made tin sulfide (SnS) as a strategic choice for next-generation PVs. In this review, limitations of leading commercial PV technologies and the status of a few alternate low-cost PV materials are outlined. Recent literature on crucial physical properties of SnS thin-films and the present status of SnS thin-film-based solar cells are discussed. Deficiency and adequacy of some of the key properties of SnS including carrier mobility (μ), minority carrier lifetime (τ), and absorption coefficient (α) are discussed in comparison of existing commercial solar cell materials. Future research trends on SnS based solar cells to enhance their conversion efficiencies towards the theoretical maximum of 24% from present ~5% and its prospectus as next-generation solar cell is also discussed.

Principal Component Analysis Applied to Gradient Fields in Band Gap Optimization Problems for Metamaterials

A promising technique for the spectral design of acoustic metamaterials is based on the formulation of suitable constrained nonlinear optimization problems. Unfortunately, the straightforward application of classical gradient-based iterative optimization algorithms to the numerical solution of such problems is typically highly demanding, due to the complexity of the underlying physical models. Nevertheless, supervised machine learning techniques can reduce such a computational effort, e.g., by replacing the original objective functions of such optimization problems with more-easily computable approximations. In this framework, the present article describes the application of a related unsupervised machine learning technique, namely, principal component analysis, to approximate the gradient of the objective function of a band gap optimization problem for an acoustic metamaterial, with the aim of making the successive application of a gradient-based iterative optimization algorithm faster. Numerical results show the effectiveness of the proposed method.

Hurdles and recent developments for CdS and chalcogenide‐based electrode in “Solar electro catalytic” hydrogen generation: A review

AbstractThere are tremendous efforts to realize the idea of employing photoelectrochemical (PEC) technology for generating chemical energy from solar energy. The most important feature of this technology is to coordinate the energetics of an electrochemical reaction with the solar spectrum. So, the photoelectrochemistry of a semiconducting material plays a vital role in this arena. Exploring an efficient and stable semiconductor material for such purpose is an essential prospect. There are several sulfide selenide‐based semiconductors viz. II‐VI (Zn/Cd = S/Se) semiconductors those exhibit high potential in PEC application. Nonetheless, they suffer by certain corrosion issues, which are important to be reviewed and are discussed here. This review highlights the significant role of cadmium chalcogenides among various materials explored in this technology. CdS is the most studied system among all those with perfect band gap and band‐edge position exhibiting material, desired for photoanode in PEC cell. Next, recent progresses achieving enhancement in the performance of CdS photoanodes by doping, modifying the surface, morphology reconstruction, and engraving heterostructure is discussed in detail. The role of the nanostructured techniques, improved photo electrochemistry with redox couples, and advanced interfacial and band gap engineering is explored to overcome the lack of chemical stability of CdS. The review concludes with the bright scope of CdS as an efficient PEC material in the form of combined semiconductor systems with an optimum band gap, bandedge, and their complimentary properties rather than a single component material.

The synergic effects of light harvesting and separation of charge carriers, and the optimal band gap of photocatalysts by investigating Bi8V2O17, Bi4V2O11, BiVO4 and Bi4V6O21

The light harvesting and separation of charge carriers are two decisive factors in the photocatalytic process. In order to reveal the synergic effects of light absorption and separation of charge carriers, and put forward the optimal band gaps of specific photocatalytic systems, Bi8V2O17, Bi4V2O11, BiVO4 and Bi4V6O21 series samples with the V/Bi = 0.25, 0.5, 1 and 1.5 were successfully designed and synthesized. UV–Vis diffuse reflectance spectra (DRS) indicated that the visible light harvesting was tremendously enhanced with the increase of V/Bi ratio. Due to the narrow down of band gaps, photoluminescence (PL) illustrated that the separation of electron-hole pairs was gradually restrained. Although Bi8V2O17 showed the best separation of electron-hole pairs, and Bi4V6O21 had the best light harvesting range, but the photocatalytic experiments showed that the optimal sample is Bismuth vanadate (BiVO4). Density functional theory (DFT) calculation has been utilized to explain the above inconsistency, and a promising formula has been put forward to calculate the regularity of light harvesting and separation of electron-hole pairs in the photocatalytic systems. This work constructed the relation between light absorption and separation of electron-hole pairs, and creatively proposed a reliable band gap calculation method to forecast and design of efficient photocatalysts.

Copper zinc tin sulfide and multi-walled carbon nanotubes nanocomposite for visible-light-driven photocatalytic applications

Photocatalytic activity of hydrothermally synthesized CZTS-MWCNT hetero structured NCs was investigated here. The CZTS NPs and CZTS-MWCNT NCs of varying MWCNT contents (3 wt%, 6 wt% and 9 wt%) were characterized by XRD, SEM, TEM, Raman and UV–Vis spectroscopy. The TEM image confirmed that the CZTS NPs are anchored to MWCNTs. From the UV–Vis spectroscopy, the optimum optical band gap of CZTS-6 wt% MWCNT NCs was found 1.4 eV and exhibited higher absorption than CZTS NPs. Under visible light radiation, photocatalytic dye degradation of methylene blue studies revealed a 19% higher photodegradation efficiency for CZTS-6 wt% MWCNT NCs than CZTS NPs. CZTS-6 wt% MWCNT NCs achieved a reaction rate constant of 0.012 min−1, which is twice that of CZTS NPs. Because of the optimal bandgap of CZTS and the rapid charge carrier mobility of MWCNTs, CZTS-MWCNT NCs have the advantage of enhancing photocatalytic activity over CZTS NPs.

Dimension-Dependent Bandgap Narrowing and Metallization in Lead-Free Halide Perovskite Cs3Bi2X9 (X = I, Br, and Cl) under High Pressure.

Low-toxicity, air-stable cesium bismuth iodide Cs3Bi2X9 (X = I, Br, and Cl) perovskites are gaining substantial attention owing to their excellent potential in photoelectric and photovoltaic applications. In this work, the lattice constants, band structures, density of states, and optical properties of the Cs3Bi2X9 under high pressure perovskites are theoretically studied using the density functional theory. The calculated results show that the changes in the bandgap of the zero-dimensional Cs3Bi2I9, one-dimensional Cs3Bi2Cl9, and two-dimensional Cs3Bi2Br9 perovskites are 3.05, 1.95, and 2.39 eV under a pressure change from 0 to 40 GPa, respectively. Furthermore, it was found that the optimal bandgaps of the Shockley–Queisser theory for the Cs3Bi2I9, Cs3Bi2Br9, and Cs3Bi2Cl9 perovskites can be reached at 2–3, 21–26, and 25–29 GPa, respectively. The Cs3Bi2I9 perovskite was found to transform from a semiconductor into a metal at a pressure of 17.3 GPa. The lattice constants, unit-cell volume, and bandgaps of the Cs3Bi2X9 perovskites exhibit a strong dependence on dimension. Additionally, the Cs3Bi2X9 perovskites have large absorption coefficients in the visible region, and their absorption coefficients undergo a redshift with increasing pressure. The theoretical calculation results obtained in this work strengthen the fundamental understanding of the structures and bandgaps of Cs3Bi2X9 perovskites at high pressures, providing a theoretical support for the design of materials under high pressure.

Solution processed AgSbS2 film for efficient planar heterojunction solar cells

AgSbS2 is a promising absorber material for photovoltaic cells because of its optimum bandgap, strong optical absorption, and excellent stability. Here, we report a spin-coating and annealing approach for the fabrication of AgSbS2 solar cells, where Ag-Sb-thiourea complex solution was prepared as the precursor solution. We identified that the annealing temperature crucially affected the phase composition, crystallinity, and surface morphology of the AgSbS2 film. We also probed the electronic structures and established a FTO/TiO2/AgSbS2/Spiro-OMeTAD/Au device structure. This device finally achieved an encouraging power conversion efficiency of 2.25%, which is highest efficiency in AgSbS2 solar cells. Our research opens up another prospect for pursuing high performance AgSbS2 thin film solar cells by adopting a solution processing method and planar heterojunction device structure.

Exfoliation method matters: The microstructure-dependent photoactivity of g-C3N4 nanosheets for water purification

Exfoliation of carbon nitride (g-C3N4) into an ultrathin nanostructure significantly improves its photoactivity. However, the effects of the exfoliation method on the microstructure and photocatalytic performance of g-C3N4 nanosheets remain largely unknown. Herein, several typical strategies, such as thermal, chemical, ultrasonic and one-step exfoliation, were applied to exfoliate g-C3N4 nanosheets for photocatalytic applications. A procedure capable of controlling the morphology, microstructure, light-absorption property, and visible light photoactivity of g-C3N4 nanosheets was attempted. We found that nanosheets prepared from one-step exfoliation present superior photocatalytic efficiency under visible light than those fabricated by thermal exfoliation and ultrasonic exfoliation. The kinetic constants for bisphenol A (BPA) photodegradation over these samples were determined to be 6.5, 4.5 and 2.3 times higher than bulk g-C3N4, respectively. For chemical exfoliation, excessive oxidation by H2SO4 can lead to the structural defects and deactivation of urea-derived g-C3N4 nanosheets. Carbon nitride nanosheets synthesized by one-step exfoliation exhibited high specific surface area, optimal band gap energy structure, and high charge separation efficiency, thereby increasing visible-light photoactivity. Enabling cost-effective production of ultrathin and robust g-C3N4 nanosheets, one-step exfoliation offers a potential strategy to exploit high-performance g-C3N4 for water purification applications.

Deposition and characterization of stannite Cu2FeSn(S0·8Se0.2)4 thin film for potential absorber layer in solar cell application

This work investigates the properties of CFTSSe material synthesized by melt quench technique and subsequent thin film deposition using thermal evaporation method. To study the compositional, structural, morphological and optical properties of the material, various characterization techniques like XRD, SEM, EDS, Raman spectroscopy, FTIR and UV–Vis–NIR spectroscopy have been applied. These studies show that CFTSSe is crystalline in nature and consistent with the stannite structure. Whereas some large density electronic defects have been detected in the lattice. UV visible spectroscopy estimates a high absorption coefficient (>104 cm−1) and optimal band gap of 1.49 eV. Additionally, the properties of CFTSSe are also compared with our previous study of CZTSSe and appeared to have potential to be used in thin film solar cell applications.

Effect of copper precursor layer thickness on the properties of preferentially oriented Cu4SnS4 thin films for photovoltaic applications

Copper tin sulfide (Cu–Sn–S) thin films have gathered great attention in the research for earth-abundant, non-toxic, and low-cost thin film solar cells. In this investigation, preferentially oriented Cu 4 SnS 4 thin films have been fabricated via a combination of chemical bath deposition and thermal evaporation for the first time. Stacked precursor layers of thermally evaporated copper and chemically deposited SnS thin films were annealed in the sulfur atmosphere at a temperature of 823 K for 1 h. The copper layer thickness was varied from 150 to 200 nm. Various characterization techniques were employed to study the structure, morphology, optical and electrical properties of the Cu 4 SnS 4 films (XRD, Raman, FE-SEM, AFM, UV–Vis spectroscopy) formed at different conditions. The orthorhombic structured films formed at the best conditions showed highly oriented growth along (102) plane. An intense peak at 316 cm −1 in the Raman spectrum further confirmed the formation of the Cu 4 SnS 4 phase. The crystalline sizes and bandgap energies of deposited films varied between 33.6 and 52.7 nm and 1.0–1.6 eV, respectively. The sample with a copper precursor layer thickness of 185 nm exhibited an optimum bandgap of 1.4 eV and larger grains implies that a copper layer of 185 nm in thickness on 200 nm SnS is an optimal precursor layer thickness for achieving highly oriented Cu 4 SnS 4 thin film with excellent properties. • First attempt to fabricate Cu 4 SnS 4 thin films via a combination of physical-chemical deposition methods. • Cu 4 SnS 4 thin films with novel preferential orientation along (102) plane. • Optimization of copper precursor layer thickness resulted enhanced crystallinity. • The optimum bandgap of 1.4 eV for photovoltaic applications.

HTL-Free Sb2(S, Se)3 Solar Cells with an Optimal Detailed Balance Band Gap

Antimony chalcogenides are widely studied as a light-absorbing material due to their merits of low toxicity, efficient cost, and excellent photovoltaic properties. However, the band gaps of antimony selenide (approximately 1.1 eV) and antimony sulfide (approximately 1.7 eV) both deviate from the optimal detailed balance band gap (∼1.3 eV) for terrestrial single-junction solar cells. Notably, the band gap of Sb2(S, Se)3 can be tunable in the range from 1.1 to 1.7 eV, which can cover the detailed balance band gap. In this work, the vapor transport deposition method with two independent evaporation sources is used to deposit Sb2(S, Se)3 thin films. By carefully optimizing the evaporation temperature and the start evaporation time of the Sb2Se3 and Sb2S3 sources, a suitable band gap of 1.33 eV is obtained. Finally, on the basis of the optimal Sb2(S, Se)3 films, Sb2(S, Se)3 solar cells without a hole transport layer achieved an efficiency of 7.03%.

Photo-thermo catalytic selective oxidation of cyclohexane by In-situ prepared nonstoichiometric Molybdenum oxide and Silver-palladium alloy composite

The highly selective oxidation of cyclohexane to cyclohexanone and cyclohexanol (KA oil) is one of the most challenging issues in the chemical industry. However, the difficulty in attaining high selectivity and high conversion rate in parallel for the existing catalysts limits its practical application. In this paper, a novel photo-thermo synergistic catalyst was reported for the aerobic oxidation of cyclohexane. The uniform blue MoO3-x nanowires with small diameter stabilized by polyvinyl pyrrolidone (PVP) were synthesized by a hydrothermal method, and a series of MoO3-x-AgPd composite materials of different proportions were prepared by an in-situ reduction process. The morphology, crystalline structure, surface chemical bonding, photoelectrochemical properties of MoO3-x-AgPd composites are thoroughly characterized. The MoO3-x-AgPd composites present significantly increased catalytic performance than MoO3-x nanowires in the photo-thermo synergistic catalytic oxidation of cyclohexane under dry air. The high conversion rate of 11.3% with the KA oil selectivity of 99.0% was achieved by the MoO3-x-Ag20Pd20 composites under photo-thermo catalytic process at 120 ℃, which is 1.5 times of that by MoO3-x nanowires. Under photo-thermo catalytic process, a high cyclohexane conversion rate similar to that of higher temperature thermal catalysis can be obtained at lower reaction temperature, and more cyclohexanol can be produced with a ketone to alcohol (K/A) ratio of 0.254. The significantly enhanced catalytic activity can be attributed to the effective charge transfer in the AgPd alloy nanoparticles, the optimized band gap structure, the suppressed charge recombination, and the promoted photo-thermo synergetic catalytic effect. This work provides a new reference scheme for the design and preparation of high-efficiency photo-thermo catalysts for the selective oxidation of cyclohexane.

Synthesis and Characterization of Cu2ZnSnS4 Thin Films Obtained by Combined Magnetron Sputtering and Pulsed Laser Deposition.

Cu2ZnSnS4 (CZTS) is a complex quaternary material, and obtaining a single-phase CZTS with no secondary phases is known to be challenging and dependent on the production technique. This work involves the synthesis and characterization of CZTS absorber layers for solar cells. Thin films were deposited on Si and glass substrates by a combined magnetron sputtering (MS) and pulsed laser deposition (PLD) hybrid system, followed by annealing without and with sulfur powder at 500 °C under argon (Ar) flow. Three different Cu2S, SnS2, and ZnS targets were used each time, employing a different target for PLD and the two others for MS. The effect of the different target arrangements and the role of annealing and/or sulfurization treatment were investigated. The characterization of the absorber films was performed by grazing incidence X-ray diffraction (GIXRD), X-ray reflectometry (XRR), Raman spectroscopy, scanning electron microscopy, and regular transmission spectroscopy. The film with ZnS deposited by PLD and SnS2 and Cu2S by MS was found to be the best for obtaining a single CZTS phase, with uniform surface morphology, a nearly stoichiometric composition, and an optimal band gap of 1.40 eV. These results show that a new method that combines the advantages of both MS and PLD techniques was successfully used to obtain single-phase Cu2ZnSnS4 films for solar cell applications.

Phononic Bandgap Optimization in Sandwich Panels Using Cellular Truss Cores

The development of custom cellular materials has been driven by recent advances in additive manufacturing and structural topological optimization. These contemporary materials with complex topologies have better structural efficiency than traditional materials. Particularly, truss-like cellular structures exhibit considerable potential for application in lightweight structures owing to their excellent strength-to-mass ratio. Along with being light, these materials can exhibit unprecedented vibration properties, such as the phononic bandgap, which prohibits the propagation of mechanical waves over certain frequency ranges. Consequently, they have been extensively investigated over the last few years, being the cores for sandwich panels among the most important potential applications of lattice-based cellular structures. This study aims to develop a methodology for optimizing the topology of sandwich panels using cellular truss cores for bandgap maximization. In particular, a methodology is developed for designing lightweight composite panels with vibration absorption properties, which would bring significant benefits in applications such as satellites, spacecraft, aircraft, ships, automobiles, etc. The phononic bandgap of a periodic sandwich structure with a square core topology is maximized by varying the material and the geometrical properties of the core under different configurations. The proposed optimization methodology considers smooth approximations of the objective function to avoid non-differentiability problems and implements an optimization approach based on the globally convergent method of moving asymptotes. The results show that it is feasible to design a sandwich panel using a cellular core with large phononic bandgaps.

Effect of heat treatment on the characteristics and NH3 Sensing properties of Tin Dioxide SnO2 Thin Film

In this research, Spray pyrolysis technique used to prepared Tin dioxide (SnO2) thin films on glass substrate with thickness about 200± 8 nm by dissolved 2.2563 g of SnCl2.2H2O in 100 ml of ethanol then added 60 drops from concentrated hydrochloric acid (HCl). After that the films were annealed at different temperatures (300, 400 and 400 °C ). X-ray analyses shows that the structure of all SnO2 films is polycrystalline with tetragonal rutile crystalline structure with preferential orientation in the direction (200).The optical measurements show that the optical transition has been direct and the average band gap has been tendency to decreases from 3.98 eV to 3.73 eV with increasing of Ta. The extent and nature of transmittance and optimized band gap of the material assure to utilize it for sensor applications.From sensing measurements for NH3 gas at different operating temperature (100,200,250 and 300)°C and gas concentration 1(5%, 10%, 15%, 20%, 25%, 30%, and 35% ) can be seen that the sensitivity increases with increasing operating temperature and gas concentration, the response time decreases to smallest value (4s) at operating temperature 200 °C while the recovery time (22 s).

Use of metamodels for rapid discovery of narrow bandgap oxide photocatalysts

SummaryNew photocatalysts are traditionally identified through trial-and-error methods. Machine learning has shown considerable promise for improving the efficiency of photocatalyst discovery from a large potential pool. Here, we describe a multi-step, target-driven consensus method using a stacking meta-learning algorithm that robustly predicts bandgaps and H2 evolution activities of photocatalysts. Trained on small datasets, these models can rapidly screen a large space (>10 million materials) to identify promising, non-toxic compounds as candidate water splitting photocatalysts. Two effective compounds and two controls possessing optimal bandgap values (∼2 eV) but not photoactivity as predicted by the models were synthesized. Their experimentally measured bandgaps and H2 evolution activities were consistent with the predictions. Conspicuously, the two compounds with strong photoactivities under UV and visible light are promising visible-light-driven water splitting photocatalysts. This study demonstrates the power of machine learning and the potential of big data to accelerate discovery of next-generation photocatalysts.

Comparative Study of Recombination Dynamics in Optimized Composition of Sn- Versus Pb-Based Perovskite Solar Cells.

The energy band gaps of Pb halide perovskites are higher than the optimal band gap required for single-junction solar cells, governed by the Shockley-Queisser radiative limit. The pure Sn and Pb-Sn mixed-based perovskites have drawn significant attention due to their ability to lead to lower band gaps and open a new door for all perovskite tandem applications. There has been continuous progress toward the rapid improvement in the power conversion efficiency of Sn and Pb-Sn mixed-based perovskite solar cells (PSCs). Along with efforts for efficiency, it is worth analyzing the in-depth recombination dynamics for further development of Sn-based PSCs. The lower bimolecular recombination rate constant (k) is often attributed to the high performance of PSCs. Herein, we study the role of "B" cations in charge carrier recombination dynamics (CCRD) of ABX3 (A = MA+, FA+, and Cs+; B = Pb2+, Sn2+, and X = I-)-based PSCs. We fabricated p-i-n configuration-based FA0.95Cs0.05PbI3 (pure Pb), MA0.20FA0.75Cs0.05SnI3 (pure Sn), and (MAPbI3)0.4(FASnI3)0.6 (Pb-Sn mixed) PSCs and compared the CCRD of all the three PSCs. We optimized the Sn-based perovskite thin film (pure Sn) in terms of moisture and thermal stability in order to minimize the error due to perovskite degradation. We note that despite having lower open-circuit voltage (VOC), a pure Sn-based PSC shows lower k than that of Pb-Sn mixed and pure Pb-based PSCs, which is a contradictory result. This slow relaxation lifetime of the charge carrier in Sn-based PSCs can be correlated with recombination through the defect states without introducing the quasi-Fermi-level splitting. Furthermore, our results suggest that the rate law of charge carrier decay has nonlinear dependence of k on n in Sn-based PSCs, whereas it is linear in the other two cases.

Co-precipitation Synthesis with a Variation of the Sulphur Composition of Kesterite Phase Cu2ZnSnS4 (CZSS) without Annealing Process

Commercially available compound CuInGa (S, Se) can be replaced with emerging quaternary compound Cu2ZnSnS4 (Copper Zinc Tin Sulphur or CZSS) for photovoltaic applications due to the high absorption coefficient and optimum bandgap. Unstable sulphur and the co-existence of binary and ternary phases in CZSS are the main obstacles for a single-phase kesterite quaternary compound. To overcome these issues, the researchers are synthesising the CZSS in presence of sulphur and selenium environment. The sulphurization and selenization are the constraints for the synthesis of CZSS and these processes make it costlier. In the present work, the wet-chemical method (i.e., co-precipitation method) was used to synthesise CZSS without vacuum annealing where the sulphur constituent was controlled by changing the stoichiometric ratio. X-ray diffraction (XRD) and Raman analysis confirm that the synthesised CZSS was in polycrystalline and single-phase kesterite nature. The average crystallite sizes for thiourea 16, 18, 20 mmol were found 15 nm, 17 nm and 17 nm, respectively. Surface morphology of the as-prepared film was identified by scanning electron microscope (SEM) and optical bandgap of the film was obtained ~1.33 eV by UV-visible (UV-vis) analysis. The 18 mmol of thiourea with stoichiometric ratio 4:2:2:9 is found the best optimisation for synthesising the CZSS without vacuum annealing by the co-precipitation method. Thus, the thin film of such synthesised CZSS may be employed for the low-cost photovoltaic application.

Band gap Engineering of ZnO via transition metal Doping: An ab initio study

Ab initio density functional theory calculations are performed to calculate the electronic and optical properties of transition metal doped ZnO, in order to achieve optimum bandgap reduction required for a potential photocatalyst. Geometry optimization analysis reveals that Fe, Cr, Mn and Nb doped systems are the most stable structures among our studied materials, which are further investigated for their aforementioned properties. The analysis of the Cr doped system show the maximum decrease in the bandgap and a red shift toward the visible region due to the valence electrons, suggesting that Cr doped ZnO is substantially a promising photocatalytic material for dye degradation applications.