[论文解读] Analysis of the structural characteristics and optoelectronic properties of CaTiO3 as a non-toxic raw material for solar cells: a DFT study

D. D. Nematov, Amondulloi Burhonzoda+1 more|arXiv (Cornell University)|Oct 26, 2022

Microwave Dielectric Ceramics Synthesis被引用 6

一句话总结

本DFT研究探讨了CaTiO3多晶型相（α、β、γ相）的结构与光电性能，作为太阳能电池的无毒候选材料。采用GGA和TB-mBJ近似，研究发现正交相最稳定，带隙为3.26 eV，而立方相表现出最高的吸收能力和光电导率，表明尽管带隙较宽，仍具有潜在的光伏应用前景。

ABSTRACT

Structural and optoelectronic properties of α, \{beta}, 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. It is shown that as the transition from the α-phase to the γ-phase proceeds, the lattice constant parameters and the interatomic distance in these systems increase. 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.

研究动机与目标

• 通过第一性原理计算评估CaTiO3多晶型相（α、β、γ）的结构稳定性及相变行为。
• 确定CaTiO3最热力学稳定的相，并将其晶格参数与实验数据进行比较。
• 分析所有相的能带结构和态密度等光电性能。
• 评估CaTiO3作为无毒、宽带隙半导体在太阳能电池应用中的潜力。
• 比较不同相在吸收系数和光电导率等光学性能方面的差异。

提出的方法

• 采用Wien2k程序包，基于广义梯度近似（GGA）进行第一性原理密度泛函理论（DFT）计算，实现结构优化。
• 应用TB-mBJ近似以提高能带结构计算中交换关联势的精度。
• 通过几何优化确定各相的弛豫晶格参数和原子间距离。
• 计算电子能带结构和态密度（DOS），分析其半导体特性及电子跃迁行为。
• 从介电函数计算光学常数，包括吸收系数和光学电导率，以评估其光伏潜力。
• 对CaTiO3的立方（α）、四方（β）和正交（γ）相进行对比分析。

实验结果

研究问题

• RQ1 根据DFT计算，CaTiO3的哪种多晶型相最热力学稳定？
• RQ2 CaTiO3的α、β和γ相在晶格参数和原子间距离方面有何差异？
• RQ3 CaTiO3的立方、四方和正交相的带隙值分别是多少？与实验值相比如何？
• RQ4 哪种相在费米能级附近具有最高的态密度？这对载流子生成意味着什么？
• RQ5 三种相在可见光范围内的光学吸收和光电导率性能有何不同？

主要发现

• CaTiO3的正交相（γ相）最稳定，其晶格参数与实验值高度吻合。
• 带隙从立方相（α相）的2.83 eV逐渐增加至四方相（β相）的3.07 eV，最终达到正交相（γ相）的3.26 eV。
• 四方相在费米能级附近具有最高的态密度，表明其具有更强的电子态，有利于电荷传输。
• 立方相表现出最高的吸收能力及相对较高的光电导率，表明其在太阳能电池中具有更优的光捕获潜力。
• 四方相与正交相的光学吸收和光电导率光谱几乎完全一致，表明其具有相似的光电性能。
• 所有三种相均为宽带隙半导体，其中立方相因表现出更优越的光学响应，最适合作为光伏应用的候选材料。