钙钛矿合金研究新利器：自动化工作流程

在材料科学领域，金属卤化物钙钛矿（MHPs）材料因其高功率转换效率在光伏应用中备受关注。然而， MHPs的内在化学不稳定性是实现持久器件的一个挑战，这其实也是实施合金策略的一大动机，如将Cs阳离子与有机候选物混合形成A_1−xCs_xPbI₃（A = MA，FA）。

在这一点上，通过经验方法将MHPs的多晶型性质与其电子性质相关联并不简单，这在合金环境中可能受到阻碍。因此，通过适当构建MHP合金的一个热力学系综，开发一套从头计算协议来捕获这种多晶型特性是一个广泛的领域，同时，自动化程序非常希望加速这些系统的数据采集（特别是在工业中）。

Fig. 2 | Cluster distances.

来自巴西巴拉那联邦大学化学系的Luis Octavio de Araujo等，提出了一种基于 SimStack 框架的自动化工作流程，运用广义准化学近似（GQCA）等方法，实现了对A_1-xCs_xPbI₃（A=MA，FA）伪立方合金全面深入的研究。该流程可精确计算合金热力学性质、相图、光电特性及功率转换效率，并纳入关键相对论效应。

作者系统分析了有机和无机阳离子混合对合金结构与电子特性的影响，揭示了阳离子特性对格拉泽旋转及合金稳定性的作用机制，得到不同成分合金的稳定条件及相关热力学数据，并计算出了不同合金在特定成分下的功率转换效率，如MA_1-xCs_xPbI₃（0.50<x<1.00）和A_1-xCs_xPbI₃（0.0<x<0.20）在室温下的高效率表现。

Fig. 4 | Cluster excess energies calculated via APD.

该研究不仅明确了成分和多晶型程度对 MHP 合金稳定性和光电性能的关键影响，且证实了SimStack工作流程在理解此类材料方面的有效性，为未来钙钛矿合金研究及优化提供了重要依据，有助于推动其在太阳能电池等领域的发展。该文近期发表于npj Computational Materials 10: 146(2024)。

Fig. 5 | Mixing free energies as a function of the alloy composition and temperature.

Editorial Summary

In the field of materials science, metal halide perovskites (MHPs) have attracted much attention in photovoltaic applications due to their high power conversion efficiency. However, the intrinsic chemical instability of MHPs in correlation with the operation long-time is a challenge for the accomplishment of durable devices, which is the motivation to implement alloying strategies involving Cs cations with organic candidates to form A_1−xCs_xPbI₃ (e.g., A = MA, FA). In this regard, the causality correlation between the polymorphic nature of MHPs in operando and their electronic properties through empirical approaches is not trivial, which is potentially hampered in the alloying context. Therefore, there is a wide field to develop ab initio protocols to capture this associated polymorphism through a proper construction of the thermodynamic ensemble of MHP alloys, at the same time, automation procedures are highly desirable to accelerate data acquisition (especially in industry) from those systems. 

Luis Octavio de Araujo et al. from the Department of Chemistry, Federal University of Paraná, Brazil, introduced an automated workflow based on the SimStack framework, using methods such as the generalized quasi-chemical approximation (GQCA) to achieve a comprehensive and in-depth study of the pseudo-cubic alloy A_1-xCs_xPbI₃. This workflow can accurately calculate the thermodynamic properties, phase diagrams, optoelectronic characteristics, and power conversion efficiency of the alloy, and incorporate key relativistic effects. The authors systematically analyzed the influence of the mixing of organic and inorganic cations on the structure and electronic properties of the alloy. They revealed the mechanism of the effect of cation characteristics on Glazer rotations and the stability of the alloy, obtained the stable conditions and related thermodynamic data of alloys with different compositions, and calculated the power conversion efficiencies of different alloys under specific compositions. For example, the high-efficiency performance of MA_1-xCs_xPbI₃ (0.50<x<1.00) and A_1-xCs_xPbI₃ (0.0<x<0.20) at room temperature. 

This study not only clarifies the crucial influence of composition and polymorphic degree on the stability and optoelectronic properties of MHP alloys but also confirms the effectiveness of the SimStack workflow in understanding such materials. It provides an important basis for future research and optimization of perovskite alloys and helps promote their development in fields such as solar cells. This article was published in npj Computational Materials 10: 146(2024).

原文Abstract及其翻译

Automated workflow for analyzing thermodynamic stability in polymorphic perovskite alloys（分析多晶型钙钛矿合金热力学稳定性的自动化工作流程）

Luis Octavio de Araujo, Celso R. C. Rêgo, Wolfgang Wenzel, Maurício Jeomar Piotrowski, Alexandre Cavalheiro Dias & Diego Guedes-Sobrinho 

Abstract In this first-principles investigation, we explore the polymorphic features of pseudo-cubic alloys, focusing on the impact of mixing organic and inorganic cations on their structural and electronic properties, configurational disorder, and thermodynamic stability. Employing an automated cluster expansion within the generalized quasichemical approximation (GQCA), our results reveal how the effective radius of the organic cation (r_MA = 2.15 Å, r_FA = 2.53 Å) and its dipole moment (μ_MA = 2.15 D, μ_FA = 0.25 D), influences Glazer’s rotations in the A_1−xCs_xPbI₃ (A = MA, FA) sublattice, with MA-based alloy presenting a higher critical temperature (527 K) and being stable for x > 0.60 above 200 K, while its FA analog has a lower critical temperature (427.7 K) and is stable for x < 0.15 above 100 K. Additionally, polymorphic motifs magnify relativistic effects, impacting the thermodynamic behavior of the systems. Our methodology leverages the SimStack framework, an automated scientific workflow that enables the nuanced modeling of polymorphic alloys. This structured approach allows for comprehensive calculations of thermodynamic properties, phase diagrams, optoelectronic insights, and power conversion efficiencies while meticulously incorporating crucial relativistic effects like spin-orbit coupling (SOC) and quasi-particle corrections. Our findings advocate for the rational design of thermodynamically stable compositions in solar cell applications by calculating power conversion efficiencies using a spectroscopic limited maximum efficiency model, from which we obtained high efficiencies of about 28% (31–32%) for MA_1−xCs_xPbI₃ with 0.50 < x < 1.00 (FA_1−xCs_xPbI₃ with 0.0 < x < 0.20) as thermodynamically stable compositions at room temperature. The workflow’s significance is highlighted by a Colab-based notebook, which facilitates the analysis of raw data output, allowing users to delve into the physics of these complex systems. Our work underscores the pivotal role of composition and polymorphic degrees in determining the stability and optoelectronic properties of MHP alloys. It demonstrates the effectiveness of the SimStack workflow in advancing our understanding of these materials.

摘要 在这项第一性原理研究中，我们探索了赝立方合金的多晶型特征，重点关注有机和无机阳离子混合对其结构和电子特性、构型无序性及热力学稳定性的影响。通过在广义准化学近似（GQCA）中进行自动团簇展开，我们的结果揭示了有机阳离子的有效半径（，）及其偶极矩（，）如何影响A_1-xCs_xPbI₃ (A = MA, FA)子晶格中的格拉泽旋转。基于MA的合金具有较高的临界温度（527K），在200K以上时，当x>0.60时稳定；而其FA类似物的临界温度较低（427.7K），在100K以上时，当x<0.15时稳定。此外，多晶型基元会放大相对论效应，影响系统的热力学行为。我们的方法利用了SimStack框架，这是一种自动化科学工作流程，能够对多晶型合金进行细致入微的模拟。这种结构化方法允许对热力学性质、相图、光电特性和功率转换效率进行全面计算，同时精心纳入自旋轨道耦合（SOC）、准粒子校正等关键相对论效应。通过使用光谱限制最大效率模型计算功率转换效率，我们的结果为太阳能电池应用中热力学稳定成分的合理设计提供了依据，并由此得到在室温下MA_1-xCs_xPbI₃（0.50<x<1.00）和FA_1-xCs_xPbI₃（0.0<x<0.20）作为热力学稳定成分的效率高达约28%（31 - 32%）。基于Colab的笔记本突出了该工作流程的重要性，它便于对原始数据输出进行分析，使用户能够深入探究这些复杂系统的物理原理。我们的工作强调了成分和多晶型程度在决定金属卤化物钙钛矿（MHP）合金的稳定性和光电性能方面的关键作用。它证明了SimStack工作流程在增进我们对这些材料的理解方面的有效性。