Defect formation and healing at grain boundaries in lead-halide perovskites,Journal of Materials Chemistry A

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Defect formation and healing at grain boundaries in lead-halide perovskites
Journal of Materials Chemistry A ( IF 10.7 ) Pub Date : 2022-11-11 , DOI: 10.1039/d2ta06336k
Waldemar Kaiser ₁ , Kashif Hussain _{2,

3} , Ajay Singh ₄ , Asma A. Alothman ₅ , Daniele Meggiolaro ₁ , Alessio Gagliardi ₂ , Edoardo Mosconi _{1,

5} , Filippo De Angelis _{1,

6}

Affiliation

Polycrystalline perovskite solar cells show high power conversion efficiencies despite the presence of grain boundaries (GBs). The benign nature of GBs on the electronic properties and structural stability in metal-halide perovskites contradicts their propensity for point defect formation, a controversy that is far from being understood. In this work, we combine ab initio molecular dynamics and density functional theory calculations on the Σ5[130] GB of cesium lead iodide, CsPbI₃, to shed light on the structural and electronic properties of such GBs. Our results present the first evidence of structural healing of GBs driven by the facile migration of iodine ions, resulting in stabilized GB structures with reduced hole trap states and shallow electron trap states by strain-induced Pb–Pb dimers. Drift-diffusion simulations reveal that shallow electron trap states in GB mainly lower open-circuit voltage by enhanced non-radiative recombination. Finally, we observe the spontaneous formation of iodine Frenkel defects with reduced formation energies compared to the perovskite bulk. Overall, our study reveals a controversy of GBs showing a moderate impact on the electronic properties by structural healing but a detrimental impact on the point defect densities, both being connected to the facile migration of iodine ions in GBs.

中文翻译：

卤化铅钙钛矿晶界缺陷的形成和修复

尽管存在晶界 (GB)，多晶钙钛矿太阳能电池仍显示出高功率转换效率。GBs 对金属卤化物钙钛矿的电子特性和结构稳定性的良性性质与其形成点缺陷的倾向相矛盾，这是一个远未被理解的争议。在这项工作中，我们结合了从头算分子动力学和密度泛函理论计算对铯铅碘化物 CsPbI _{3的 Σ5[130] GB}, 以阐明此类 GB 的结构和电子特性。我们的研究结果首次证明了 GB 的结构愈合是由碘离子的轻松迁移驱动的，导致稳定的 GB 结构具有减少的空穴陷阱状态和由应变诱导的 Pb-Pb 二聚体引起的浅电子陷阱状态。漂移扩散模拟表明，GB 中的浅电子陷阱态主要通过增强的非辐射复合来降低开路电压。最后，我们观察到自发形成的碘弗仑克尔缺陷与钙钛矿块相比具有降低的形成能。总的来说，我们的研究揭示了 GB 的争议，显示结构修复对电子特性有适度影响，但对点缺陷密度有不利影响，两者都与 GB 中碘离子的容易迁移有关。

更新日期：2022-11-11

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