Strong interplay between structure and electronic properties in CuIn(S,Se){2}: a first-principles study

Correlating Optical and Structural Properties of CO on Transition Metal Surfaces

We present an optical study based on the quasiparticle self-consistent GW (QS GW ) approximation combining structural information taken from density functional theory (DFT) to elucidate spectral features of CO adsorbed on Pt(111) and Cu(111). Optical information and structural arrangement of the adsorbed CO are correlated by varying both site positions and CO coverage as compared to experimental studies (θ = 1/4 to θ = 1/2). This enables us to resolve key spectral features of both occupied and unoccupied molecular states at various adsorbate coverages, comparing theory to experiment. Using experimental data as benchmarks, we show the theory compares well with available data. Its predictive power provides a new path to infer information about the structure of CO from optical information and can help to predict the presence of other little understood adsorbates such as an OCCO dimer that may be relevant to mechanistic pathways for reduction of CO2 to high value C2 + products. This new approach complements total energy calculations and also fills a void in DFT-based theory that is known to be an unreliable predictor of the energetics of CO on transition metal surfaces.

Nonempirical dielectric dependent hybrid as an accurate starting point for the single shot G0W0 calculation of chalcopyrite semiconductors

The accuracy of quasiparticle corrections in a single-shot G0W0 calculation relies heavily on the preceding eigensystem of density functional theory (DFT). An incorrect energy spectrum obtained from the DFT calculation can result in an inaccurate quasiparticle G0W0 bandgap. This study explicitly investigates the bandgaps of chalcopyrite semiconductors within G0W0, considering various DFT approximations, including semilocal, hybrid, and nonempirical screened dielectric-dependent hybrid (DDH) as the starting point for G0W0 calculation. The superiority of G0W0 on top of screened DDH is evident in achieving highly accurate bandgaps for chalcopyrite semiconductors. In addition, when the Bethe-Salpeter equation is solved, the optical absorption spectra derived from these calculations are remarkably precise. This study demonstrates that nonempirical G0W0@DDH serves as a cost-effective and precise tool for various applications related to chalcopyrite semiconductors, particularly in cases where a self-consistent GW (scGW) calculation is challenging.

Direct Synthesis and Characterization of Hydrophilic Cu-Deficient Copper Indium Sulfide Quantum Dots

Copper indium sulfide (CIS) nanocrystals constitute a promising alternative to cadmium- and lead-containing nanoparticles. We report a synthetic method that yields hydrophilic, core-only CIS quantum dots, exhibiting size-dependent, copper-deficient composition and optical properties that are suitable for direct coupling to biomolecules and nonradiative energy transfer applications. To assist such applications, we complemented previous studies covering the femtosecond-picosecond time scale with the investigation of slower radiative and nonradiative processes on the nanosecond time scale, using both time-resolved emission and transient absorption. As expected for core particles, relaxation occurs mainly nonradiatively, resulting in low, size-dependent photoluminescence quantum yield. The nonradiative relaxation from the first excited band is wavelength-dependent with lifetimes between 25 and 150 ns, reflecting the size distribution of the particles. Approximately constant lifetimes of around 65 ns were observed for nonradiative relaxation from the defect states at lower energies. The photoluminescence exhibited a large Stokes shift. The band gap emission decays on the order of 10 ns, while the defect emission is further red-shifted, and the lifetimes are on the order of 100 ns. Both sets of radiative lifetimes are wavelength-dependent, increasing toward longer wavelengths. Despite the low radiative quantum yield, the aqueous solubility and long lifetimes of the defect states are compatible with the proposed role of CIS quantum dots as excitation energy donors to biological molecules.

First-principle investigation of structural, electronic, and phase stabilities in chalcopyrite semiconductors: insights from Meta-GGA functionals

We undertake a comprehensive first-principles investigation into the factors influencing the optoelectronic efficiencies of PIQIIIR2VIchalcopyrite semiconductors. The structural attributes, electronic properties, and phase stabilities are explored using various meta-GGA exchange-correlation (XC) functionals within the density functional framework. In particular, we assess the relative performance of these XC functionals in obtaining estimates of various relevant parameters. The structural parameteruin chalcopyrite semiconductors is a noteworthy aspect, as it is intrinsically tied to the extent of orbital hybridization between distinct atoms and thereby strongly influences the electronic properties. In general, the application of widely used GGA-PBE XC functional to these chalcopyrites results in unreliable predictions of band gaps and 'u' parameter due to delocalization errors that in turn arise due to the inclusion ofdandfcore electrons. While hybrid functionals offer remarkable accuracy through state-of-the-art methods, their main drawback lies in their computational expense and resource demands. Our findings strongly suggest that in comparison to GGA-PBE, the meta-GGA XC functionals perform quite well and provide results that closely align with experimental values. In particular, ther2SCAN andrMGGAC XC functionals are preferable and superior for investigating chalcopyrites and other solid-state systems. This preference is rooted in their excellent performance and substantially reduced computational costs compared to hybrid functionals.

Emergence of CuInS2 derived photocatalyst for environmental remediation and energy conversion

Hydrogen production, catalytic organic synthesis, carbon dioxide reduction, environmental purification, and other major fields have all adopted photocatalytic technologies due to their eco-friendliness, ease of use, and reliance on sunlight as the driving force. Photocatalyst is the key component of photocatalytic technology. Thus, it is of utmost importance to produce highly efficient, stable, visible-light-responsive photocatalysts. CIS stands out among other visible-light-response photocatalysts for its advantageous combination of easy synthesis, non-toxicity, high stability, and suitable band structure. In this study, we took a brief glance at the synthesis techniques for CIS after providing a quick introduction to the fundamental semiconductor features, including the crystal and band structures of CIS. Then, we discussed the ways doping, heterojunction creation, p-n heterojunction, type-II heterojunction, and Z-scheme may be used to modify CIS's performance. Subsequently, the applications of CIS towards pollutant degradation, CO2 reduction, water splitting, and other toxic pollutants remediation are reviewed in detail. Finally, several remaining problems with CIS-based photocatalysts are highlighted, along with future potential for constructing more superior photocatalysts.

Many-body effects in the X-ray absorption spectra of liquid water

SignificanceIn X-ray absorption spectroscopy, an electron-hole excitation probes the local atomic environment. The interpretation of the spectra requires challenging theoretical calculations, particularly in a system like liquid water, where quantum many-body effects and molecular disorder play an important role. Recent advances in theory and simulation make possible new calculations that are in good agreement with experiment, without recourse to commonly adopted approximations. Based on these calculations, the three features observed in the experimental spectra are unambiguously attributed to excitonic effects with different characteristic correlation lengths, which are distinctively affected by perturbations of the underlying H-bond structure induced by temperature changes and/or by isotopic substitution. The emerging picture of the water structure is fully consistent with the conventional tetrahedral model.

Improved electronic structure prediction of chalcopyrite semiconductors from a semilocal density functional based on Pauli kinetic energy enhancement factor

The correct treatment ofdelectrons is of prime importance in order to predict the electronic properties of the prototype chalcopyrite semiconductors. The effect ofdstates is linked with the anion displacement parameteru, which in turn influences the bandgap of these systems. Semilocal exchange-correlation functionals which yield good structural properties of semiconductors and insulators often fail to predict reasonableubecause of the underestimation of the bandgaps arising from the strong interplay betweendelectrons. In the present study, we show that the meta-generalized gradient approximation (meta-GGA) obtained from the cuspless hydrogen density (MGGAC) (2019Phys. Rev.B 100 155140) performs in an improved manner in apprehending the key features of the electronic properties of chalcopyrites, and its bandgaps are comparative to that obtained using state-of-art hybrid methods. Moreover, the present assessment also shows the importance of the Pauli kinetic energy enhancement factor,α= (τ-τ^W)/τ^unifin describing thedelectrons in chalcopyrites. The present study strongly suggests that the MGGAC functional within semilocal approximations can be a better and preferred choice to study the chalcopyrites and other solid-state systems due to its superior performance and significantly low computational cost.

First-principles study on the electronic and optical properties of Bi2WO6

Photocatalytic materials attract continued scientific interest due to their possible application in energy harvesting. These applications critically rely on efficient photon absorption and exciton physics, which are governed by the underlying electronic structure. We report the electronic properties and optical response of the Bi₂WO₆ bulk photocatalyst using first-principle methods. The density functional theory DFT-computed electronic band gap is corrected by including Hubbard potentials for W-5d and O-2p orbitals, and one of the most advanced methods, Quasi-Particle (QP) GW at different levels, with semi-core states of Bi (5s and 5p) and W (4f), carefully taken into account in GW calculations. The perplexing nature of band character of Bi₂WO₆ is examined, and it comes out to be direct at PBE level without SOC. However, it shows indirect nature at GW level or when Spin–Orbit Coupling (SOC) is turned on even at PBE level. The optical response of the material system is computed within independent-particle approximation (IPA), taking into account local field effects and employing the time-dependent DFT (TDDFT) method. Bethe–Salpeter equation (BSE) is used to capture the excitonic effect, and the results of these approximations are compared with the experimental data. Our first-principle calculations results indicate that electron–hole interaction significantly modifies optical absorption of Bi₂WO₆, thereby verifying the reported experimental observations.

The nature of the band gap obtained from SOC and QP corrections changes to indirect. The semi-core states of Bi have been proved to be crucial in the GW calculations. Optical absorption from BSE, including SOC best matches the experimental data.

Stretchable AgX (X = Se, Te) for Efficient Thermoelectrics and Photovoltaics

Transition metal chalcogenides (TMCs) have gained worldwide interest owing to their outstanding renewable energy conversion capability. However, the poor mechanical flexibility of most existing TMCs limits their practical commercial applications. Herein, triggered by the recent and imperative synthesis of highly ductile α-Ag₂S, an effective approach based on evolutionary algorithm and ab initio total-energy calculations for determining stable, ductile phases of bulk and two-dimensional Ag_xSe_1-x and Ag_xTe_1-x compounds was implemented. The calculations correctly reproduced the global minimum bulk stoichiometric P2₁2₁2₁-Ag₈Se₄ and P2₁/c-Ag₈Te₄ structures. Recently reported metastable AgTe₃ was also revealed but it lacks dynamical stability. Further single-layered screening unveiled two new monolayer P4/nmm-Ag₄Se₂ and C2-Ag₈Te₄ phases. Orthorhombic Ag₈Se₄ crystalline has a narrow, direct band gap of 0.26 eV that increases to 2.68 eV when transforms to tetragonal Ag₄Se₂ monolayer. Interestingly, metallic P2₁/c-Ag₈Te₄ changes to semiconductor when thinned down to monolayer, exhibiting a band gap of 1.60 eV. Present findings confirm their strong stability from mechanical and thermodynamic aspects, with reasonable Vickers hardness, bone-like Young's modulus (E) and high machinability observed in bulk phases. Detailed analysis of the dielectric functions ε(ω), absorption coefficient α(ω), power conversion efficiency (PCE) and refractive index n(ω) of monolayers are reported for the first time. Fine theoretical PCE (SLME method ∼11-28%), relatively high n(0) (1.59-1.93), and sizable α(ω) (10⁴-10⁵ cm^-1) that spans the infrared to visible regions indicate their prospects in optoelectronics and photoluminescence applications. Effective strategies to improve the temperature dependent power factor (PF) and figure of merit (ZT) are illustrated, including optimizing the carrier concentration. With decreasing thickness, ZT of p-doped Ag-Se was found to rise from approximately 0.15-0.90 at 300 K, leading to a record high theoretical conversion efficiency of ∼12.0%. The results presented foreshadow their potential application in a hybrid device that combines the photovoltaic and thermoelectric technologies.

In silico investigation of Cu(In,Ga)Se2-based solar cells

Photovoltaics is one of the most promising and fastest-growing renewable energy technologies. Although the price-performance ratio of solar cells has improved significantly over recent years, further systematic investigations are needed to achieve higher performance and lower cost for future solar cells. In conjunction with experiments, computer simulations are powerful tools to investigate the thermodynamics and kinetics of solar cells. Over the last few years, we have developed and employed advanced computational techniques to gain a better understanding of solar cells based on copper indium gallium selenide (Cu(In,Ga)Se2). Furthermore, we have utilized state-of-the-art data-driven science and machine learning for the development of photovoltaic materials. In this Perspective, we review our results along with a survey of the field.

Conductivity in the Square Lattice Hubbard Model at High Temperatures: Importance of Vertex Corrections

Recent experiments on cold atoms in optical lattices allow for a quantitative comparison of the measurements to the conductivity calculations in the square lattice Hubbard model. However, the available calculations do not give consistent results, and the question of the exact solution for the conductivity in the Hubbard model remained open. In this Letter, we employ several complementary state-of-the-art numerical methods to disentangle various contributions to conductivity and identify the best available result to be compared to experiment. We find that, at relevant (high) temperatures, the self-energy is practically local, yet the vertex corrections remain rather important, contrary to expectations. The finite-size effects are small even at the lattice size 4×4, and the corresponding Lanczos diagonalization result is, therefore, close to the exact result in the thermodynamic limit.

Local Bonding Influence on the Band Edge and Band Gap Formation in Quaternary Chalcopyrites

Quaternary chalcopyrites have shown to exhibit tunable band gaps with changing anion composition. Inspired by these observations, the underlying structural and electronic considerations are investigated using a combination of experimentally obtained structural data, molecular orbital considerations, and density functional theory. Within the solid solution Cu2ZnGeS4-x Se x , the anion bond alteration parameter changes, showing larger bond lengths for metal-selenium than for metal-sulfur bonds. The changing bonding interaction directly influences the valence and conduction band edges, which result from antibonding Cu-anion and Ge-anion interactions, respectively. The knowledge of the underlying bonding interactions at the band edges can help design properties of these quaternary chalcopyrites for photovoltaic and thermoelectric applications.

Compound Copper Chalcogenide Nanocrystals

This review captures the synthesis, assembly, properties, and applications of copper chalcogenide NCs, which have achieved significant research interest in the last decade due to their compositional and structural versatility. The outstanding functional properties of these materials stems from the relationship between their band structure and defect concentration, including charge carrier concentration and electronic conductivity character, which consequently affects their optoelectronic, optical, and plasmonic properties. This, combined with several metastable crystal phases and stoichiometries and the low energy of formation of defects, makes the reproducible synthesis of these materials, with tunable parameters, remarkable. Further to this, the review captures the progress of the hierarchical assembly of these NCs, which bridges the link between their discrete and collective properties. Their ubiquitous application set has cross-cut energy conversion (photovoltaics, photocatalysis, thermoelectrics), energy storage (lithium-ion batteries, hydrogen generation), emissive materials (plasmonics, LEDs, biolabelling), sensors (electrochemical, biochemical), biomedical devices (magnetic resonance imaging, X-ray computer tomography), and medical therapies (photochemothermal therapies, immunotherapy, radiotherapy, and drug delivery). The confluence of advances in the synthesis, assembly, and application of these NCs in the past decade has the potential to significantly impact society, both economically and environmentally.

Accurate description of the electronic structure of organic semiconductors by GW methods

Electronic properties associated with charged excitations, such as the ionization potential (IP), the electron affinity (EA), and the energy level alignment at interfaces, are critical parameters for the performance of organic electronic devices. To computationally design organic semiconductors and functional interfaces with tailored properties for target applications it is necessary to accurately predict these properties from first principles. Many-body perturbation theory is often used for this purpose within the GW approximation, where G is the one particle Green's function and W is the dynamically screened Coulomb interaction. Here, the formalism of GW methods at different levels of self-consistency is briefly introduced and some recent applications to organic semiconductors and interfaces are reviewed.

Defect visualization of Cu(InGa)(SeS)2 thin films using DLTS measurement

Defect depth profiles of Cu (In_1−x,Ga_x)(Se_1−yS_y)₂ (CIGSS) were measured as functions of pulse width and voltage via deep-level transient spectroscopy (DLTS). Four defects were observed, i.e., electron traps of ~0.2 eV at 140 K (E1 trap) and 0.47 eV at 300 K (E2 trap) and hole traps of ~0.1 eV at 100 K (H1 trap) and ~0.4 eV at 250 K (H2 trap). The open circuit voltage (V_OC) deteriorated when the trap densities of E2 were increased. The energy band diagrams of CIGSS were also obtained using Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and DLTS data. These results showed that the valence band was lowered at higher S content. In addition, it was found that the E2 defect influenced the V_OC and could be interpreted as an extended defect. Defect depth profile images provided clear insight into the identification of defect state and density as a function of depth around the space charge region.

Experimental and theoretical optical properties of methylammonium lead halide perovskites

The optical constants of methylammonium lead halide single crystals CH3NH3PbX3 (X = I, Br, Cl) are interpreted with high level ab initio calculations using the relativistic quasiparticle self-consistent GW approximation (QSGW). Good agreement between the optical constants derived from QSGW and those obtained from spectroscopic ellipsometry enables the assignment of the spectral features to their respective inter-band transitions. We show that the transition from the highest valence band (VB) to the lowest conduction band (CB) is responsible for almost all the optical response of MAPbI3 between 1.2 and 5.5 eV (with minor contributions from the second highest VB and the second lowest CB). The calculations indicate that the orientation of [CH3NH3](+) cations has a significant influence on the position of the bandgap suggesting that collective orientation of the organic moieties could result in significant local variations of the optical properties. The optical constants and energy band diagram of CH3NH3PbI3 are then used to simulate the contributions from different optical transitions to a typical transient absorption spectrum (TAS).

Structural, electronic, optical, vibrational and transport properties of CuBX2 (X = S, Se, Te) chalcopyrites

The structural, electronic and optical properties of CuBX₂ (X = S, Se, Te) compounds have been studied using the full-potential (linearized) augmented plane-wave (FP(L)APW) method.

Two novel silicon phases with direct band gaps

Based on density function theory with the ultrasoft pseudopotential scheme, we have systematically studied the structural stability, absorption spectra, electronic, optical and mechanical properties and minimum thermal conductivity of two novel silicon phases, Cm-32 silicon and P2₁/m silicon.

In-Situ Probing Plasmonic Energy Transfer in Cu(In, Ga)Se2 Solar Cells by Ultrabroadband Femtosecond Pump-Probe Spectroscopy

In this work, we demonstrated a viable experimental scheme for in-situ probing the effects of Au nanoparticles (NPs) incorporation on plasmonic energy transfer in Cu(In, Ga)Se2 (CIGS) solar cells by elaborately analyzing the lifetimes and zero moment for hot carrier relaxation with ultrabroadband femtosecond pump-probe spectroscopy. The signals of enhanced photobleach (PB) and waned photoinduced absorption (PIA) attributable to surface plasmon resonance (SPR) of Au NPs were in-situ probed in transient differential absorption spectra. The results suggested that substantial carriers can be excited from ground state to lower excitation energy levels, which can reach thermalization much faster with the existence of SPR. Thus, direct electron transfer (DET) could be implemented to enhance the photocurrent of CIGS solar cells. Furthermore, based on the extracted hot carrier lifetimes, it was confirmed that the improved electrical transport might have been resulted primarily from the reduction in the surface recombination of photoinduced carriers through enhanced local electromagnetic field (LEMF). Finally, theoretical calculation for resonant energy transfer (RET)-induced enhancement in the probability of exciting electron-hole pairs was conducted and the results agreed well with the enhanced PB peak of transient differential absorption in plasmonic CIGS film. These results indicate that plasmonic energy transfer is a viable approach to boost high-efficiency CIGS solar cells.

Many-body Green's function GW and Bethe-Salpeter study of the optical excitations in a paradigmatic model dipeptide

We study within the many-body Green's function GW and Bethe-Salpeter formalisms the excitation energies of a paradigmatic model dipeptide, focusing on the four lowest-lying local and charge-transfer excitations. Our GW calculations are performed at the self-consistent level, updating first the quasiparticle energies, and further the single-particle wavefunctions within the static Coulomb-hole plus screened-exchange approximation to the GW self-energy operator. Important level crossings, as compared to the starting Kohn-Sham LDA spectrum, are identified. Our final Bethe-Salpeter singlet excitation energies are found to agree, within 0.07 eV, with CASPT2 reference data, except for one charge-transfer state where the discrepancy can be as large as 0.5 eV. Our results agree best with LC-BLYP and CAM-B3LYP calculations with enhanced long-range exchange, with a 0.1 eV mean absolute error. This has been achieved employing a parameter-free formalism applicable to metallic or insulating extended or finite systems.

Strong renormalization of the electronic band gap due to lattice polarization in the GW formalism

The self-consistent GW band gaps are known to be significantly overestimated. We show that this overestimation is, to a large extent, due to the neglect of the contribution of the lattice polarization to the screening of the electron-electron interaction. To solve this problem, we derive within the GW formalism a generalized plasmon-pole model that accounts for lattice polarization. The resulting GW self-energy is used to calculate the band structures of a set of binary semiconductors and insulators. The lattice contribution always decreases the band gap. The shrinkage increases with the size of the longitudinal-transverse optical splitting and it can represent more than 15% of the band gap in highly polar compounds, reducing the band-gap percentage error by a factor of 3.

Stability of the bandgap in Cu-poor CuInSe₂

Recent photoluminescence studies report that the bandgap energy E(g) ≈ 1.0 eV of CuInSe(2) is stable for Cu-poor compounds [Cu]/[In] < 1, despite the fact that Cu vacancies and (In(Cu) + 2V(Cu)) complexes increase the energy gap. In this work, the impact on E(g) due to the presence of native defects is analyzed using a screened hybrid density functional approach. We demonstrate that the formation energy of neutral (Cu(In) + In(Cu)) anti-site dimers decreases for CuInSe(2) compounds when [Cu]/[In] decreases. This is explained in terms of the octet rule for the Se atoms next to the (In(Cu) + 2V(Cu)) defects. As a consequence, Cu-poor CuInSe(2) involves the large [(In(Cu) + 2V(Cu)) + (Cu(In) + In(Cu))] complexes where the anti-site defects stabilize E(g), in agreement with experimental findings.

p doping in expanded phases of ZnO: an ab initio study

The issue of p doping in nanostructured cagelike ZnO is investigated by state-of-the-art calculations. Our study is focused on one prototypical structure, namely, sodalite, for which we show that p-type doping is possible for elements of the V, VI, and VII columns of the periodic table. However, some dopants tend to form dimers, thus impairing the stability of this kind of doping. This difference of behavior is discussed, and two criteria are proposed to ensure stable p doping.

Identification of potential photovoltaic absorbers based on first-principles spectroscopic screening of materials

There are numerous inorganic materials that may qualify as good photovoltaic (PV) absorbers, except that the currently available selection principle-focusing on materials with a direct band gap of ∼1.3 eV (the Shockley-Queisser criteria)-does not provide compelling design principles even for the initial material screening. Here we offer a calculable selection metric of "spectroscopic limited maximum efficiency (SLME)" that can be used for initial screening based on intrinsic properties alone. It takes into account the band gap, the shape of absorption spectra, and the material-dependent nonradiative recombination losses. This is illustrated here via high-throughput first-principles quasiparticle calculations of SLME for ∼260 generalized I(p)III(q)VI(r) chalcopyrite materials. It identifies over 20 high-SLME materials, including the best known as well as previously unrecognized PV absorbers.

Vacancies in CuInSe2: new insights from hybrid-functional calculations

We calculate the energetics of vacancies in CuInSe(2) using a hybrid functional (HSE06, HSE standing for Heyd, Scuseria and Ernzerhof), which gives a better description of the band gap compared to (semi)local exchange-correlation functionals. We show that, contrary to present beliefs, copper and indium vacancies induce no defect levels within the band gap and therefore cannot account for any experimentally observed levels. The selenium vacancy is responsible for only one level, namely, a deep acceptor level ε(0/2-). We find strong preference for V(Cu) and V(Se) over V(In) under practically all chemical conditions.

Ab initio study of II-(VI)2 dichalcogenides

The structural stabilities of the (Zn,Cd)(S,Se,Te)(2) dichalcogenides have been determined ab initio. These compounds are shown to be stable in the pyrite phase, in agreement with available experiments. Structural parameters for the ZnTe(2) pyrite semiconductor compound proposed here are presented. The opto-electronic properties of these dichalcogenide compounds have been calculated using quasiparticle GW theory. Bandgaps, band structures and effective masses are proposed as well as absorption coefficients and refraction indices. The compounds are all indirect semiconductors with very flat conduction band dispersion and high absorption coefficients. The work functions and surface properties are predicted. The Te and Se based compounds could be of interest as absorber materials in photovoltaic applications.

Hopping conduction observed in thermal admittance spectroscopy

We observe variable-range hopping conduction in thermal admittance spectroscopy and develop a method to evaluate the signal under this condition. As a relevant example of demonstration we employ Cu(In,Ga)(Se,S)2 thin-film solar cells and show that the fundamental N1 signal, which has been discussed for more than a decade in terms of minority carrier traps, does not display trap parameters, but is generated by the freezing-out of carrier mobility with decreasing temperature when hopping conduction prevails. This effect offers a new approach to carrier hopping and to semiconductors suffering from small mobility.

Effects of electronic and lattice polarization on the band structure of delafossite transparent conductive oxides

We use hybrid functionals and restricted self-consistent GW, state-of-the-art theoretical approaches for quasiparticle band structures, to study the electronic states of delafossite Cu(Al,In)O2, the first p-type and bipolar transparent conductive oxides. We show that a self-consistent GW approximation gives remarkably wider band gaps than all the other approaches used so far. Accounting for polaronic effects in the GW scheme we recover a very nice agreement with experiments. Furthermore, the modifications with respect to the Kohn-Sham bands are strongly k dependent, which makes questionable the common practice of using a scissor operator. Finally, our results support the view that the low energy structures found in optical experiments, and initially attributed to an indirect transition, are due to intrinsic defects in the samples.