Electron Carrier Concentration Research Articles

Inorganic Lead‐Free Cs2AuBiCl6 Perovskite Absorber and Cu2O Hole Transport Material Based Single‐Junction Solar Cells with 22.18% Power Conversion Efficiency

AbstractCs2AuBiCl6 is considered to be a potential lead‐free double perovskite alternative for perovskite solar cells. Its electronic and optical properties are investigated using density functional theory. The electronic properties of Cs2AuBiCl6 material ensure a bandgap of 1.40 eV (without considering SOC) and 1.12 eV (with SOC) using mBJ exchange‐correlation functional, close to the optimal bandgap for solar cell application as per the Shockley–Queisser limit. Optical properties suggest a high absorption coefficient ≈105 cm−1 with low reflectance, making it the optimal absorber material. Furthermore, the photovoltaic performance of Cs2AuBiCl6 based single‐junction transparent conducting oxide (TCO)/IDL1/Cs2AuBiCl6/IDL2/Cu2O solar cell is investigated using SCAPS‐1D device simulation program. The impact of electron affinity, thickness, carrier concentration, defect density, and interface defect density is examined using interface defect layer (IDL) on the photovoltaic performance. The maximum photoconversion efficiency (PCE) of ≈22.18% is noticed for optimized material's parameters. These studies on TCO/IDL1/Cs2AuBiCl6/IDL2/Cu2O solar cell will provide guidelines for designing and developing an efficient lead‐free perovskite‐based solar cell as an alternative to conventional halide perovskite materials based solar cell.

Ultrahigh Power Factors in Ultrawide-Band-Gap GaB3N4 and AlB3N4 for High-Temperature Thermoelectric Applications

With recent thermoelectric studies concentrating too much on low- and mid-temperature applications, an interesting question is, “are there any materials suitable for high-temperature thermoelectric operations?” To answer this, we have demonstrated in this work the viability of the ternary ultrawide-band-gap materials GaB3N4 and AlB3N4 for high-temperature thermoelectric applications using the first-principles calculation method. Our accurate transport calculations, considering both elastic and inelastic scattering mechanisms, reveal the ultrahigh power factors as high as 1821 μW m–1 K–2 in GaB3N4 and 1876 μW m–1 K–2 in AlB3N4 at 2000 K. The power factors are calculated from the Seebeck coefficients and electrical conductivities for both electron and hole carrier concentrations between 1018 and 1021 cm–3. For the figure-of-merit (ZT) calculation, the obtained power factors along with the electronic thermal conductivities determined from the definite Lorenz numbers and the lattice thermal conductivities from the phonon vibrations were used. The calculated ZT values seem to be appreciable for high-temperature applications considering the materials’ stability factor and the temperature range within the optimum electron carrier concentration of 1021 cm–3. Although the lattice thermal conductivities are higher, which decrease the values of ZT, considering the ultrahigh power factors instead of the ZT factor could be the right choice for high-temperature thermoelectric applications.

Phase diagram of the Ag2SnS3–ZnS pseudobinary system for Ag2ZnSnS4 crystal growth

The phase equilibrium of the Ag2SnS3–ZnS pseudobinary system for the growth of Ag2ZnSnS4 (AZTS) crystals was investigated using the equilibration-quenching technique. The growth mechanism of AZTS follows the peritectic reaction liquid phase + ZnS phase ↔ AZTS phase, which occurs at a composition of ~20 mol% ZnS and a temperature of approximately 700 °C. The AZTS polycrystalline sample was obtained from the stoichiometric melt growth. The kesterite structure of the AZTS sample without secondary phases was identified by a combination of X-ray diffraction and Raman spectroscopy measurements. The electron carrier concentration and conductivity, determined by the Hall effect measurement, were (3.0–6.3) × 1015 cm−3 and (5.6–9.2) × 10−4 S/cm, respectively. The slightly Zn-rich and S-poor composition led to n-type conduction in the AZTS because of the dominant Zn antisites on Ag (ZnAg) and S vacancy (VS) defects. Therefore, this study can make a significant contribution to the research and application of AZTS materials.

High Electron and Low Heat Transports of 1D Atomic Defect Tunnels Stabilized in Tungsten Oxide Epitaxial Films

The coexistence of high electron conduction and low heat conduction are essentially important to realize efficient thermal management materials such as thermoelectric materials. Although introducing 0D point defects (Fig. a) or 2D layers (Fig. c) is known as an effective way to reduce the heat conduction, there is a dilemma that the electron conduction is also reduced due to that electrons and phonons are scattered simultaneously by impurities, defects, and boundaries. Here we show that introducing a 1D atomic defect tunnel is an excellent solution to solve this dilemma. (Fig. b) In this structure, the probability of that phonon hits the 1D atomic defect tunnel or wire is much higher than that of introducing 0D defect or dot event though 1D defect density is low. In order to verify this hypothesis experimentally, we selected oxygen deficient tungsten oxide epitaxial film as the candidate material. The WO x films (2.7 < x < 3.0) were heteroepitaxial grown by the pulsed laser deposition technique on (001) and (110) LaAlO3 single crystal substrates under oxygen atmosphere. The oxygen pressure was precisely controlled from 2 to 13 Pa during the deposition. As a result, we found that 1D atomic defect tunnels can be introduced in tungsten oxide epitaxial films by oxygen removal. In order to visualize the atomic arrangement of the WO x films, high-angle annular dark-field (HADDF) scanning transmission electron microscopy (STEM) was performed. The resultant WO x epitaxial films contain 1D atomic defect tunnel in the in-plane direction and the density increased with decreasing x. The thermal conductivity (κ) of the films drastically decreased from ~7 W m-1 K-1 to ~1.5 W m-1 K-1 in order to minimize κ with increasing 1D defects. The κ values of WO x films are close to that of amorphous WO x , which shows minimum κ. On the other hand, the electrical conductivity (σ) in the in-plane direction of WO x film dramatically increased from ~10-1 S cm-1 to ~103 S cm-1. Since the oxygen removal reduces the valence state of tungsten, carrier electron concentration increases with increasing 1D defects. The introduction of 1D defect tunnels does not affect the electron propagation but selectively suppresses only the phonon propagation most likely due to the fact that mean free path is much shorter for the carrier electron compared to the phonon. Thus, high electron conduction and low heat conduction coexist in oxygen-deficient tungsten oxide epitaxial films. The present finding would be useful to design efficient thermal management materials such as thermoelectric materials. Figure 1

Co-sensitization of metal based N719 and metal free D35 dyes: An effective strategy to improve the performance of DSSC

Abstract The co-sensitization of dye sensitizers has been demonstrated as a potential way to improve the efficiency of DSSC, because of its positive effects such as reducing dye aggregation on TiO2 surface, suppressing charge recombination, and improving the open circuit voltage. In this work, we realized that the co-adsorption of ruthenium based N719 dye and organic D35 dye has enhanced the electron relaxation lifetime, carrier concentration, and charge separation in TiO2 photoanode, thus improving the performance of DSSCs. The high efficiency of 8% was obtained in DSSC with dye co-sensitization than its single dye based DSSCs (6.9% for N719 and 6.5% for D35).

Theoretical investigation of twin boundaries in WO3 : Structure, properties, and implications for superconductivity

We present a theoretical study of the structure and functionality of ferroelastic domain walls in tungsten trioxide, WO$_3$. WO$_3$ has a rich structural phase diagram, with the stability and properties of the various structural phases strongly affected both by temperature and by electron doping. The existence of superconductivity is of particular interest, with the underlying mechanism as of now not well understood. In addition, reports of enhanced superconductivity at structural domain walls are particularly intriguing. Focusing specifically on the orthorhombic $\beta$ phase, we calculate the structure and properties of the domain walls both with and without electron doping. We use two theoretical approaches: Landau-Ginzburg theory, with free energies constructed from symmetry considerations and parameters extracted from our first-principles density functional calculations, and direct calculation using large-scale, GPU-enabled density functional theory. We find that the structure of the $\beta$-phase domain walls resembles that of the bulk tetragonal $\alpha_1$ phase, and that the electronic charge tends to accumulate at the walls. Motivated by this finding, we perform ab initio computations of electron-phonon coupling in the bulk $\alpha_1$ structure and extract the superconducting critical temperatures , $T_c$, within Bardeen-Cooper-Schrieffer theory. Our results provide insight into the experimentally observed unusual trend of decreasing Tc with increasing electronic charge carrier concentration.

Mixed Ionic–Electronic Conductor of Perovskite LixLayMO3−δ toward Carbon‐Free Cathode for Reversible Lithium–Air Batteries

AbstractMixed ionic–electronic conductors (MIECs) can play a pivotal role in achieving high energies and power densities in rechargeable batteries owing to their ability to simultaneously conduct ions and electrons. Herein, a new strategy is proposed wherein late 3d transition metals (TMs) are substituted into a perovskite Li‐ion conductor to transform it into a Li‐containing MIEC. First‐principles calculations show that perovskite LixLayMO3 with late 3d TMs have a low oxygen vacancy formation energy, implying high electron carrier concentrations corresponding to high electronic conductivity. The activation barriers for Li diffusion in LixLayMO3 (M = Ti, Cr, Mn, Fe, and Co) are below 0.411 eV, resulting in high Li‐ion conductivity. The designed perovskites of Li0.34La0.55MnO3−δ experimentally prove to have high electronic (2.04 × 10−3 S cm−1) and Li‐ion (8.53 × 10−5 S cm−1) conductivities, and when applied in a carbon‐free cathode of a Li–air cell, they deliver superior reversibility at 0.21 mAh cm−2 over 100 charge/discharge cycles while avoiding the degradation associated with carbonaceous materials. This strategy enables the effective design of Li‐conducting MIEC and reversible Li–air batteries.

Study on the carrier transport mechanism in single-crystalline Br-doped SnSe2

We investigate the carrier transport mechanism in Br-doped SnSe2 single crystals by characterizing electrical properties in the high-temperature (T) region (300–500 K). In-plane electrical resistivity decreases with the introduction of Br dopant in layered SnSe2 single crystals owing to the increase of the electron carrier concentration (ne), indicating Br is an efficient electron donor for SnSe2. From the T dependence of ne, the thermally activated behavior disappears when ne exceeds approximately 1018 cm−3, suggesting degenerate conduction easily occurs by electron doping from 300 to 500 K. The Hall carrier mobility (μH) depends on T according to the relation μH ~ T−γ, and γ is significantly reduced from 1.68 to 0.52 by Br doping. This strongly evidences that the homopolar optical mode phonon, as the main scatterer for carrier transport at high T, is effectively quenched through the carrier doping.

Composition formula of transparent conductive tin doped indium oxide in terms of cluster plus glue atom model

Abstract As transparent electrode, the tin (Sn) doped indium oxide (In2O3) film has been widely used in the photo-electric and electric-photo conversion devices. While, the relation between carrier concentration and Sn doping content in Sn doped In2O3 (ITO) film hasn’t be revealed satisfactorily enough. In this article, the so-called ‘cluster plus glue atom’ model was first used to describe In2O3 and ITO. Based on the definition rule of cluster, the principal and unit cluster formula of In2O3 were [In–O6]In3 and ([In–O6]In3)-([In–O6]In3)6-([In–O6]In3), respectively. Then, with the lowest Sn doping content, the unit cluster formula and composition formula of ITO could be expressed as ([Sn–O6]In3)-([Sn–O6]In3) ([In–O6]In3)5-([Sn–O6]In3) and Sn3In29O48, respectively. The unit cluster of ITO showed Sn/In atom ratio of 10.34 at.%, which corresponded well with that of commercial ITO material (10.30 at.%). Based on ITO unit cluster, the theoretical optimal value of ITO electron carrier concentration could reach 2.9 × 1021 (/cm3). Actually, the experimental value of electron carrier concentration of ITO was lower than 1/3 of the theoretical optimal one. The difference between theoretical optimal value and experimental value of ITO electron carrier concentration was discussed based on the unit cluster formula of ITO. Finally, with the better understanding of ‘cluster plus glue atom’ model, the new type of transparent conductive oxide materials could be designed and applied in future.

Electrochemical Semiconductor Analysis By Square Wave Voltammetry

Studies in the past 20 years have utilized cyclic voltammetry (CV) for determining various electronic properties (e.g. density of states, electron carrier concentrations, trap state capacitances) of semiconducting titanium oxide films in photoelectrocatalytic systems such as dye-sensitized solar cells [1-4]. Though primarily used for redox sensing, this work presents square wave voltammetry (SWV) as an alternative to determining said properties. As an electrochemical characterization technique, SWV can provide significantly less background current and greater sensitivity than CV [5]. This is beneficial for the accurate measurement and calculation of electronic properties from electrochemical semiconductor current-voltage data. By varying the applied frequency as well as step and/or pulse sizes of the square wave, one can probe electronic processes of various time scales, in contrast to CV which only allows control of the potential scanning rate across the same potential window [5, 6]. This work presents a comparative study of electronic properties as determined by SWV versus CV for various semiconducting electrodes such as silicon, germanium, titanium oxide, and doped diamond films. This technique was also extended to semiconductor heterostructures - such as noble metal-decorated titanium oxide - for observation of intraband gap states and their contribution to the overall electronic properties of the electrode as determined by SWV.[1] Liu, B. et. al., “Intrinsic intermediate gape states of TiO2 materials and their roles in charge carrier kinetics”, J. Photochem. and Photobio. C: Photochem. Rev., 39 (2019) 1-57[2] Zare, M., Mortezaali, A., and Shafiekhani, A., “Photoelectrochemical determination of shallow and deep trap states of platinum-decorated TiO2 nanotube arrays for photocatalytic applications”, J. Phys. Chem. C, 120 (2016) 9017-9027[3] Fabregat-Santiago, F. et al., “High carrier density and capacitance in TiO2 nanotube arrays induced by electrochemical doping”, J. Am. Chem. Soc., 130 (2008), 11312-11316[4] Abayev, I. et al., “Properties of the electronic density of states in TiO2 nanoparticles surrounded with aqueous electrolyte”, J. Solid State Electrochem, 11 (2007) 647-653[5] Mirceski, V. et al., ”Square-wave voltammetry: A review on the recent progress”, Electroanalysis, 25 (2013) 2411-2422[6] Bard, A. J. and Faulkner, L. R., Electrochemical Methods: Fundamentals and Applications, 2nd ed. Hoboken, NJ: John Wiley & Sons, Inc., 2001.

Defects controlled doping and electrical transport in TiS2 single crystals

TiS2 has been intensively studied as an electrode material and a thermoelectric material for energy storage and conversion applications due to its high electrical conductivity. Understanding the influence of defects on electrical transport is of importance not only to resolve the long-standing question concerning the nature of TiS2, but also for the rational design of TiS2 based devices for energy scavenging applications. In this study, we integrate photoemission spectroscopy, Raman spectroscopy, and electrical transport measurements to determine the chemical compositions dominated by defects and their influence on the doping and electrical properties. Our results demonstrate that TiS2 is a heavily self-doped semiconductor with the Fermi level close to the conduction band, which serves as the conclusive experimental evidence regarding the semiconducting nature of TiS2. The doping effect is sensitive to the (subtle) changes in the chemical composition. The electron donation from the Ti interstitials (Tii) to the TiS2 host explains the high carrier concentration. The Ti Frenkel pair (TiF) acting as the acceptor is responsible for the decrease in the electron carrier concentration and electrical conductivity. High conductivity maintains upon partial oxidization, indicating the oxidization-tolerance in terms of the electronic structure. Our results provide valuable insight into the evolution of electronic properties modulated by defects that reveal unambiguously the self-doped semiconducting nature of TiS2 and chemical- and environment-tolerance of TiS2 as an advanced energy scavenging material.

Preparation, thermoelectric properties, and crystal structure of boron-doped Mg2Si single crystals

Mg2Si is a potential thermoelectric (TE) material that can directly convert waste energy into electricity. In expectation of improving its TE performance by increasing electron carrier concentration, the element boron (B) is doped in Mg2Si single crystals (SCs). Their detailed crystal structures are definitely determined by using white neutron holography and single-crystal x-ray diffraction (SC-XRD) measurements. The white neutron holography measurement proves that the doped B atom successfully substitutes for the Mg site. The SC-XRD measurement confirms the B-doping site and also reveals the presence of the defect of Si vacancy (VSi) in the B-doped Mg2Si SCs. The fraction of VSi increases with increasing B-doping concentration. In the case of B-doped Mg2Si polycrystals (PCs), VSi is absent; this difference between the SCs and PCs can be attributed to different preparation temperatures. Regarding TE properties, the electrical conductivity, σ, and the Seebeck coefficient, S, decreases and increases, respectively, due to the decrease in the electron carrier concentration, contrary to the expectation. The power factor of the B-doped Mg2Si SCs evaluated from σ and S does not increase but rather decreases by the B-doping. The tendencies of these TE properties can be explained by considering that the donor effect of the B atom is canceled by the acceptor effect of VSi for the B-doped Mg2Si SCs. This study demonstrates that the preparation condition of Mg2Si should be optimized to prevent the emergence of an unexpected point defect.

Influence of Fast Neutron Irradiation on the Electrical and Optical Properties of Li Doped ZnSnO Thin Film Transistor

The effects of fast neutron irradiation on the electrical and optical properties of Li (3 at%) doped ZnSnO (ZTO) thin films fabricated using a sol-gel process are investigated. From the results of Li-ZTO TFT characteristics according to change of neutron irradiation time, the saturation mobility is found to increase and threshold voltage values shift to a negative direction from 1,000 s neutron irradiation time. X-ray photoelectron spectroscopy analysis of the O 1s core level shows that the relative area of oxygen vacancies is almost unchanged with different irradiation times. From the results of band alignment, it is confirmed that, due to the increase of electron carrier concentration, the Fermi level (EF) of the sample irradiated for 1,000 s is located at the position closest to the conduction band minimum. The increase in electron concentration is considered by looking at the shallow band edge state under the conduction band edge formed by fast neutron irradiation of more than 1,000 s.

Control of the Thermoelectric Properties of Mg2Sn Single Crystals via Point-Defect Engineering

Mg2Sn is a potential thermoelectric (TE) material that can directly convert waste heat into electricity. In this study, Mg2Sn single-crystal ingots are prepared by melting under an Ar atmosphere. The prepared ingots contain Mg vacancies (VMg) as point defects, which results in the formation of two regions: an Mg2Sn single-crystal region without VMg (denoted as the single-crystal region) and a region containing VMg (denoted as the VMg region). The VMg region is embedded in the matrix of the single-crystal region. The interface between the VMg region and the single-crystal region is semi-coherent, which does not prevent electron carrier conduction but does increase phonon scattering. Furthermore, electron carrier concentration depends on the fraction of VMg, reflecting the acceptor characteristics of VMg. The maximum figure of merit zTmax of 1.4(1) × 10−2 is realised for the Mg2Sn single-crystal ingot by introducing VMg. These results demonstrate that the TE properties of Mg2Sn can be optimised via point-defect engineering.

Enhanced Thermoelectric Performance in N‐Type Mg3.2Sb1.5Bi0.5 by La or Ce Doping into Mg

AbstractN‐type Mg3.2Sb1.5Bi0.5 materials are prepared by cation‐site doping with lanthanides (La, Ce). Both La‐ and Ce‐doped samples exhibit a higher doping limit and greater efficiency than those of chalcogen (Te, Se, S)‐doped n‐type Mg3.2Sb1.5Bi0.5 samples. High electron carrier concentration ≈9 × 1019 cm−3 is obtained in Mg3.18La0.02Sb1.5Bi0.5 and Mg3.185Ce0.015Sb1.5Bi0.5, which is close to the theoretical doping‐concentration limit and induces contributions from more electron bands. A higher electrical conductivity was thus obtained and is beneficial to the enhanced ZT values for lanthanide‐doped Mg3.2Sb1.5Bi0.5. The highest ZT value ≈1.6 is achieved in Mg3.19La0.01Sb1.5Bi0.5 at 693 K, along with a ZT ≈1.50 in Mg3.19Ce0.01Sb1.5Bi0.5 at 693 K, indicating that lanthanides provide a promising doping strategy for Mg3.2Sb1.5Bi0.5‐based materials.

Carrier mediated ferromagnetism in Ga2O3:Cr

The magnetic properties of Cr impurities in β-Ga2O3 are investigated by band-gap corrected density-functional calculation. We show that Cr impurities carry a local spin magnetic moment, but in the absence of external doping exhibit no magnetic interaction. Under n-type doping conditions, however, a strong and directional long-range ferromagnetic interaction emerges, which diminishes again as carrier electron concentration is increased beyond a threshold. These results indicate carrier-mediated ferromagnetism in Cr-doped β-Ga2O3.

Self-Doping Effect in FeSe Superconductor by Pressure-Induced Charge Transfer

Several unambiguous experimental observations clearly showed that the critical temperature of FeSe superconductor depends significantly on the microstructure. Experiments also showed that the critical temperature can be greatly enhanced by the application of external pressure. The present paper deals with the effect of pressure on charge transfer and self-doping properties of the superconducting compound FeSe, based on the investigation of the pressure dependence of the Fermi surface by means of first-principles methods. From the numerically evaluated electronic and crystalline properties, the pressure-induced modifications of the FeSe Fermi surface’s topology are determined. The Luttinger theorem was also used to evaluate the carrier concentration on the Fe atomic sites from the evolution of the Fermi surface. We have found that the electronic density at the Fe sites increases with the increase in external pressure, following the distortion of Fermi surface. Our simulations reveal that the pressure-induced charge transfer from Se atoms to Fe atoms in the FeSe superconductor can be interpreted as a direct correlation between the electron carrier concentration and the applied pressure. The pressure dependence of superconducting properties of FeSe can be reasonably ascribed to a self-doping effect. The predictions about the electronic density on the Fe sites (reaching a value of 0.1, where the corresponding pressure is about 8.6 GPa) are in good agreement with experimental data available in literature. The interpretation of the pressure-induced Tc enhancement in FeSe caused by the electron transfer and self-doping effect is carried out, which can be the correct approach to explain the Tc behavior under a wide type of mechanical loading.

Band structure, thermoelectric properties, effective mass and electronic fitness function of two newly discovered 18 valence electrons stable half-Heusler TaX(X=Co,Ir)Sn semiconductors: A density functional theory approach

We performed detailed first-principles Density Functional Theory (DFT) Calculations of electronic band structure and predict the effective mass as well as the electronic fitness function S2στ(NV)−23 in the valence and conduction band edges of two Tantalum–Tin based Half-Heusler Alloys. Implementation of a generalized gradient approximation based DFT coupled with Boltzmann's transport theory allows us to determine the power factor at an appropriate chemical potential (and consequently, an optimum carrier concentration) at which other transport properties were determined. In the pure compounds, the electronic fatbands, both in the valence and conduction bands revealed the great influence of the 3-d orbitals of Cobalt atoms in lowering of the energy band gap of compound, while the 5-d Iridium orbitals contribute very little to energy gap lowering. The Seebeck coefficient is found to be hole dependent as well as having a strong dependence on temperature as it decreases with increasing electron carrier concentration in both compounds. At some high temperatures, the Seebeck coefficient developed high shoulders in the Ir-based compound at high hole concentrations close to 1022cm−3. We found the Co-based compound to be a better thermoelectric, since the Seebeck coefficient shows a heavy-doped traits, while the Ir-based compound demonstrates a parabolic-shaped Seebeck coefficient (which is a sign of a lightly-doped thermoelectric). From the effective mass calculations, we found that an increase in carrier concentrations results in lowering of the effective mass in the conduction band.

Influence of Pd Doping on Electrical and Thermal Properties of n-Type Cu0.008Bi2Te2.7Se0.3 Alloys.

Doping is known as an effective way to modify both electrical and thermal transport properties of thermoelectric alloys to enhance their energy conversion efficiency. In this project, we report the effect of Pd doping on the electrical and thermal properties of n-type Cu0.008Bi2Te2.7Se0.3 alloys. Pd doping was found to increase the electrical conductivity along with the electron carrier concentration. As a result, the effective mass and power factors also increased upon the Pd doping. While the bipolar thermal conductivity was reduced with the Pd doping due to the increased carrier concentration, the contribution of Pd to point defect phonon scattering on the lattice thermal conductivity was found to be very small. Consequently, Pd doping resulted in an enhanced thermoelectric figure of merit, zT, at a high temperature, due to the enhanced power factor and the reduced bipolar thermal conductivity.

Spray Deposition of n-type Cobalt-Doped CuO Thin Films: Influence of Cobalt Doping on Structural, Morphological, Electrical, and Optical Properties

The effects of cobalt (Co)-doping (0 at%, 2 at%, 4 at%, 6 at%, and 10 at%) on the structural, morphological, electrical, and optical characteristics of spray-deposited nanostructured copper oxide (CuO) thin films were investigated. X-ray diffraction patterns revealed that the crystallite size is subject to a constant reduction with an increase in the doping concentration. Based on field-emission scanning electron microscopy images, no change was observed for the grain shapes; however, the grain size decreased with an increase in the doping concentration. Furthermore, doping Co led to a conversion from a fairly weak p-type conductivity for the undoped CuO thin film (3.42 × 10−4 Ω cm) to a considerable n-type conductivity for the 10 at% Co-doped CuO (CuO:Co) film (4.20 × 10−1 Ω cm). Although the mobility of the resulting films decreased with Co doping, it seems that the significant enlargement in free electron carrier concentration is responsible for conductivity transition and improvement. Finally, the bandgap values were estimated using experimental data of transmittance and reflectance.