Investigating the naturally occurring forms of TiO2 on electronic and optical properties using OLCAO-MGGA-TBO9: a hybrid DFT study

Performance analysis of un-doped and doped titania (TiO 2 ) as an electron transport layer (ETL) for perovskite solar cells

CONTEXT

Density functional theory (DFT) calculations are carried out on pure and doped rutile TiO2 . The bandgap (Eg ) for pristine, S-doped, Fe-doped, and Fe/S co-doped materials is direct, with values of 2.98 eV, 2.18 eV, 1.58 eV, and 1.40 eV. The effective mass of charge carriers (m*) and ratio of effective masses of holes to effective masses of electrons (R) are also investigated, and it is discovered that Fe/S co-doped materials have the lowest charge carrier recombination rate. The Fe/S co-doped material has the highest ε ( ω ) . α ( ω ) of doped materials shifted into the visible range. Due to the high dopant concentration in Fe and Fe/S-doped cases, the Eg is lowered to a relatively small value; hence, only pristine and S-doped materials are verified as electron transport layer (ETL). A solar cell device analysis employing pure and S-doped rutile TiO2 as ETL is completed using DFT-derived parameters in SCAPS-1D modeling software for the first time. For the optimized solar cells, current-voltage (IV) characteristics, quantum efficiency (QE), capacitance-voltage (CV) characteristics, and capacitance-frequency (Cf) characteristics are provided. The aim of the present study is to improve efficiency of perovskite solar cell by doping as well as to improve accuracy of simulation by applying DFT extracted parameters as input. From the analysis, improvement is found in efficiency of doped TiO2 compared to un-doped TiO2 . The efficiency of the PSC with S-doped ETL is 1.418% higher than the PSC with un-doped ETL.

METHOD

Quantumwise Automistic Tool Kit (ATK) is used to extract DFT parameters. Using these DFT parameters as input in SCAPS-1D (Solar Cell Capacitance Simulator), solar cells for doped and un-doped material are simulated. The density functional theory (DFT)-based orthogonalized linear combination of atomic orbital (OLCAO) technique is used. Structural optimization is done using the LBFGS (Limited-memory Broyden-Fletcher-Goldfarb-Shanno). PBESol-GGA (Perdew-Burke-Ernzerhof solid-generalized gradient approximation) is applied as exchange correlation for calculating structural parameters, while MGGA-TB09 (meta-generalized gradient approximation-Tran and Blaha) is applied as exchange correlation for calculating optical and electronic properties.

Theoretical investigation on un-doped and doped TiO2 for solar cell application

Enhancing solar cell efficiency is one of the most challenging and demanding topics for PV researchers. An ab initio study is done here on the structure of crystal, formation energies, electronic structure, the density of states, effective mass, and optical properties of pure and S-doped, Fe-doped, and Fe-/S-doped anatase TiO2. Co-doping causes a significant reduction in the bandgap, suppresses the charge carrier’s recombination rate, and shifted absorption spectra from UV to the visible region. Hence, co-doped anatase TiO2 with Fe and S is more favorable as a buffer layer of the solar cell compared to S-doped and Fe-doped TiO2. The forecasted values of all quantities will benefit researchers to examine these materials for further photovoltaic applications.

DFT based studies on the structural, electronic and optical properties of LiNbO3 using some hybrid techniques

Structural, electronic, and optical properties of ferroelectric material, Lithium niobate (LiNbO3) are explored and studied using two different techniques namely, OLCAO-MGGA-TB09+c and OLCAO-GGA-PBES + U under the framework of density functional theory (DFT). The electronic properties such as band diagram, the effective mass of charge carriers, the total density of state (TDOS), and partial density of state (PDOS) are investigated in depth. Band gap values obtained using MGGA-TB09+c is 3.79 eV whereas, it is 3.78 eV for GGA-PBES + U. Furthermore, several optical properties such as dielectric constant, reflectivity, refractive index, optical conductivity, loss function, and absorption coefficient have also been extracted. It is seen that the results so obtained are consistent with experimental data which shows the soundness of our calculations. From the statistical analysis, it is found that both the techniques provide very good results on electronic and optical properties of LiNbO3 compared to existing computational work as both give an approximation of experimental data. The methods presented here will be useful for researchers to get accurate results on structural, electronic, and optical properties of other materials.