1 Analysis of the structural characteristics and optoelectronic properties of CaTiO 3 as a non -toxic raw material for solar cells a DFT study

2025-04-30 0 0 384KB 13 页 10玖币

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Analysis of the structural characteristics and optoelectronic properties

of CaTiO3 as a non-toxic raw material for solar cells: a DFT study

Nematov D.D., Burhonzoda A.S., Shokir F.

S.U.Umarov Physical -Technical Institute of the National Academy of Sciences of Tajikistan

Abstract: Structural and optoelectronic properties of α, β, γ phases of calcium titanate

are studied with the implementation of first-principles quantum-chemical calculations in the

framework of DFT. When optimizing the geometry, the GGA approximation was used. The

relaxed lattice parameters obtained by us are identical with the experimental analogs. It has

been established that the most stable phase of calcium titanate is the orthorhombic syngony,

which corresponds to the results of experimental measurements. The optoelectronic properties

of these materials have been studied using the Wien2k code. The high-precision TB-mBJ

approximation was used to calculate the exchange-correlation effects. An analysis of the

electronic properties of these materials showed that all the studied phases of calcium titanate

belong to the class of wide-gap semiconductors. The calculated band gaps for the cubic,

tetragonal, and orthorhombic CaTiO3 systems are 2.83, 3.07, and 3.26 eV, respectively.

According to the analysis of DOS-plots, it was found that the tetragonal phase of calcium

titanate is characterized by the highest density of states. Calculations of the optical constants

of the systems under study showed that the CaTiO3 cubic system is characterized by an

increased absorption capacity and a relatively high photoconductivity. However, for the other

two phases of calcium titanate, the calculations gave identical patterns, i.e., the absorption and

optical conductivity spectra of the tetragonal and orthorhombic CaTiO3 systems practically

coincide.

Keywords: density functional theory, perovskite, calcium titanate, optical properties,

photoconductivity.

1. Introduction

In the process of human activity, technology and industry develop and

improve various areas of people's lives on earth, but along with the steady

development of science and technology, such global problems as environmental

pollution and climate warming are exacerbated day by day [1]. On the other

hand, the world's non-renewable energy resources, such as hydrocarbon fuels,

are being depleted at a high rate. Obviously, these problems pose a great threat

to humanity and the development of life on Earth, and failure to take the

necessary measures in the future may make life on the planet difficult or even

impossible. In this regard, humanity needs to find alternative ways to solve these

problems and how to quickly prevent the accelerated destruction of energy

resources and global warming, as well as the melting of large glaciers.

One of the most effective ways to combat global warming is to replace

fossil fuels with new energy-efficient materials and various renewable energy

sources [1]. Based on this, the developed countries of the world, especially the

countries of Europe, from year to year increase their investments in this area, so

that scientists and engineers of the world as soon as possible develop modern

means and new weapons to combat atmospheric pollution and achieve

sustainable development of technologies and green energy [2]. The very idea of

developing new energy-efficient materials and switching to renewable energy

sources is in line with the UN strategy to prevent global problems (paragraphs 7

and 13 of the Sustainable Development Strategy) for the period up to 2030 [3].

There are several viable renewable energy sources, among which

photovoltaic generators are considered the most promising method of replacing

fossil fuels. Photovoltaic generators are based on semiconductor materials,

which in recent years have been obtained from polycrystalline and

monocrystalline silicon compounds. Thanks to this, the efficiency of silicon

solar cells has reached 26.1% in recent years [4], but despite this, there are a

number of problems, such as complex methods for the synthesis and processing

of crystals, the presence of photochemical degradation and a relatively high

price, which obliges scientists and researchers around the world to develop new,

more advanced, cheap and highly efficient materials.

In the process of developing optimal materials, scientists and engineers

have found another alternative way out - to use the unique properties of calcium

titanate [5]. This is how tandem photovoltaic cells were born, in which the

perovskite layer worked in parallel with the electroactive silicon layer. In

addition, calcium titanate is cheaper to produce commercially and easier to

manufacture. However, in the beginning, scientists did not pay enough attention

to these compounds and were engaged in the search and development of other

materials. Further, new generation perovskite solar cells have been developed

and spread very rapidly in the past few years due to the outstanding photovoltaic

properties of the organo-inorganic perovskite layer and the exceptional efforts of

scientists and engineers to research and improve their properties [6]. For

example, in 2009, research by Miyasaki and others used hybrid lead perovskite

CH3NH3PbI3 (MAPbI3) as light absorbers in solar cells and demonstrated an

energy efficiency of 3.8%. [7]. Over the years, scientists have proposed other

varieties of lead organic-inorganic perovskites, as well as their flexible panels,

which have been put into large-scale operation day after day. However, the

efficiency share of these hybrid-organo-inorganic perovskites rapidly increased

from 3.8% [8] to 25.7% [4] from 2009 to 2021, rivaling silicon solar cells in

efficiency [9]. On the other hand, despite the high efficiency of solar panels,

these materials have the problem of stability and toxicity due to the presence of

lead in their composition, which limited the further step of their

commercialization [10]. Then, in search of an alternative, the researchers again

returned to the old and well-known natural perovskite based on calcium titanate.

Calcium titanate (CaTiO3) is one of the wide-gap semiconductor

perovskites (the only natural, but ineffective) with the general formula ABX3,

where the A cation occupies a cuboctahedral position, and the B cation

octahedral. X is a halide anion [11]. In addition to semiconductor properties,

CaTiO3 also exhibits dielectric properties with a relative permittivity of up to

186 and a band gap of 3–4 eV, which can be used as an optoelectronic device

[12]. Depending on the phase transition temperature, CaTiO3 can be divided into

four space groups: orthorhombic (Pbnm), orthorhombic (Cmcm), tetragonal

(I4/mcm), and cubic (Pm3m). Among them, the cubic phase is formed at a high

temperature (T > 1300°C), and the tetragonal phase is a transition compound

that can only form at a very limited temperature (1250°C < T < 1349°C). The

orthorhombic phase (Pbnm) is stable at room temperature [13].

Interest in this mineral, as a potential semiconductor for photovoltaic

systems, arose only in the 21st century, with the advent of thin-film

technologies. The very first experiments confirmed that perovskite solar cells

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1AnalysisofthestructuralcharacteristicsandoptoelectronicpropertiesofCaTiO3asanon-toxicrawmaterialforsolarcells:aDFTstudyNematovD.D.,BurhonzodaA.S.,ShokirF.S.U.UmarovPhysical-TechnicalInstituteoftheNationalAcademyofSciencesofTajikistanAbstract:Structuralandoptoelectronicpropertiesofα,β,γphasesofcalci...

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1 Analysis of the structural characteristics and optoelectronic properties of CaTiO 3 as a non -toxic raw material for solar cells a DFT study

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