Computer modelling of novel perovskite halides for next-generation solar cells

金属卤化物钙钛矿因其在低成本、高性能和可扩展的光伏（PV）设备中的应用而引起了巨大的兴奋。这些材料具有一般的ABX3结构，其中A是单阳离子（甲基铵，MA；甲脒，FA；和/或铯，Cs）， B是双阳离子（通常是Pb）， X是阴离子（通常是I或I/Br混合物）。与晶体硅相比，钙钛矿通过改变化学成分提供低温可加工性和带隙可调性。在10年内，钙钛矿太阳能电池的功率转换效率（PCE）从3%上升到25%以上，这是前所未有的。然而，存在明显的稳定性问题，并且对基础缺陷，离子传输和界面性质的充分理解是不完整的。因此，我们还没有释放这些材料的全部性能潜力。b)目的和目标本项目将通过Saiful Islam教授（SI）领导的多方面计算方法解决这类特殊材料的关键挑战，其主要目标如下：(i)阐明离子迁移的活化能和扩散系数，并将其与一流的钙钛矿（FA,Cs）PbI3作为适当的参考系统进行比较。（ii）比较和对比界面处离子积累对电流输运和器件稳定性的影响。（iii）阐明a位阳离子掺杂和二维结构如何减轻离子迁移和表面反应，并制定最佳成分的设计指南，从而实现工业相关性。c)研究方法的新颖性本项目的特别优势将是(i)利用一系列密度泛函数理论（DFT）和分子动力学（MD）方法的能力（例如VASP， LAMMPS代码）；（ii）高性能超级计算机（如Archer-2）的有效利用，以及（iii）与牛津物理实验工作的密切协同关系。此外，新兴的人工智能（AI）和机器学习技术也将有新的应用，这些技术为研究新的光伏材料提供了创新的能力，有望实现量子力学精度和预测能力，同时比传统方法快许多个数量级。对于这样的材料建模工作，牛津大学拥有优秀的内部计算设施，SI可以通过HPC材料化学联合会（SI是Co-I）广泛访问国家Archer-2超级计算机。该项目属于EPSRC的“能源和脱碳”主题和研究领域：“太阳能技术”和“能源应用材料”。因此，该项目与EPSRC的战略目标非常一致，表明了“新材料的利用”和“太阳能技术的重大进步源于基础材料科学”。e)参与该项目的任何公司或合作者将与Henry Snaith FRS教授和Laura Herz教授（两人都在牛津物理学院附近）的钙钛矿太阳能电池小组的互补实验研究联系起来。牛津光伏公司成立于2010年，是牛津大学的一个分支机构，旨在将混合光伏商业化，并已开发出钙钛矿-硅串联效率为bbbb29 %，超过了硅的记录性能。

a) Brief description of the context of the researchMetal halide perovskites are generating enormous excitement for their use in low-cost, high-performance and scalable photovoltaic (PV) devices. These materials have the general ABX3 structure, where A is a mono-cation (methylammonium, MA; formamidinium, FA; and/or cesium, Cs), B is a di-cation (typically Pb), and X is an anion (typically I or an I/Br mixture). In contrast to crystalline silicon, perovskites offer low-temperature processability and band gap tunability through modifications of the chemical composition. Within 10 years, there has been an unprecedented rise in the power conversion efficiency (PCE) of perovskite solar cells from 3% to over 25%. However, there are significant stability issues and a full understanding of the underpinning defect, ion transport and interfacial properties is incomplete. Hence, we have yet to unlock the full performance potential of these materials.b) Aims and objectivesThis project will address critical challenges of this extraordinary class of material through a multi-faceted computational approach led by Prof Saiful Islam (SI) with the following key objectives: (i) To elucidate the activation energies and diffusion coefficients for ion migration across multiple compositions (partial A-cation substitution vs mixed I/Br) with comparison to the best-in-class perovskite (FA,Cs)PbI3 as an appropriate reference system.(ii) To compare and contrast how ion accumulation at the interfaces influence current transport and device stability. (iii) To elucidate how A-site cation doping and 2D structures can mitigate ion migration and surface reactions, and to formulate design guidelines for optimum compositions, enabling industrial relevance.c) Novelty of the research methodologyParticular strengths of this project will be (i) the ability to harness a range of density functional theory (DFT) and molecular dynamics (MD) methods (e.g. VASP, LAMMPS codes), (ii) the effective exploitation of high-performance supercomputers (e.g. Archer-2), and (iii) the close synergistic relationship with experimental work in Oxford Physics. In addition, there will be the novel use of emerging artificial intelligence (AI) and machine learning techniques which offer innovative capabilities for studying new PV materials, promising quantum-mechanical accuracy and predictive power, whilst being many orders of magnitude faster than conventional methods. For such materials modelling work, Oxford has excellent in-house computational facilities and SI has extensive access to the national Archer-2 supercomputer through the HPC Materials Chemistry Consortium (SI is Co-I).d) Alignment to EPSRC's strategies and research areas This project falls within the EPSRC 'Energy and Decarbonation' theme and the research areas: 'Solar Technology' and 'Materials for Energy Applications'. Hence, this project aligns well with EPSRC strategic objectives indicating the 'utilisation of new materials' and that 'significant advances in solar technology have arisen from underpinning materials sciences'. e) Any companies or collaborators involvedThis project will have links to complementary experimental studies on perovskite solar cells in the groups of Prof Henry Snaith FRS and Prof Laura Herz (both nearby in Oxford Physics). There will also be industry interactions with Oxford-PV, which was founded in 2010 as a spinout from the University of Oxford to commercialise hybrid photovoltaics and have developed a perovskite-on-silicon tandem efficiency of > 29%, exceeding that of the record performance of silicon.