Nature Communications | 钙钛矿不稳定的“纳米起点”找到了：Cs富集三叉晶界是关键薄弱点

FA-Cs混合阳离子钙钛矿是高效钙钛矿太阳能电池的主力体系，但其环境稳定性仍是长期痛点。过去研究多在微米或宏观尺度观察阳离子迁移、相分离和降解，却难以回答一个关键问题：降解究竟从哪里开始？ 近日发表于 Nature Communications 的研究利用准原位低剂量扫描透射电镜（STEM），把视角推进到纳米甚至原子尺度，发现 Cs富集的晶粒三叉晶界 是FA-Cs钙钛矿在环境暴露下的本征薄弱点，并据此提出NOST添加剂稳定策略。

01 问题：不是所有晶界都一样，三叉晶界更“脆弱”

为此，团队用FIB制备平面和截面样品，结合低剂量STEM与EELS mapping，直接观察纳米尺度阳离子分布。结果发现：原始薄膜中Cs和N分布并不均匀，部分晶界和三叉晶界出现Cs富集、N信号降低；截面器件样品中同样存在沿厚度方向的Cs不均一。也就是说，三叉晶界处的Cs富集在降解前就已存在，是后续相分离的“起点”。

Phase separation process of FA-Cs perovskite films under ambientstress. a Annular dark field (ADF)-STEM image and corresponding EELS mappingresults for plan-view PSC sample and intensity line profiles of Cs-M and N-K edgesalong the rectangle. Thewhite dotted lines and arrows indicate respectively theGBsand nano-pinhole like defects. Scale bar, 500 nm.b, cQuasi-in situ low-dose ADFSTEMimaging and EELS mapping results of Cs-M forcross-sectional PSC sample.The white dotted lines indicate the GBs. Scale bar, 500 nm.DQuasi-in situ low-doseSTEM imaging of phase separation process. The white arrows and circles indicatethe position of as-existed and newly formed pinhole-like defects during ambientexposure, respectively. The yellowand orange dotted lines indicate the positions ofδ-CsPbI3 formed at as-existed and newly formed pinhole-like defects, respectively.Scale bar, 500 nm. The right panel presents the nano-beam diffractions extractedfrom the regions 1-3 marked in image vi. Scale bar, 5nm−1. e Schematic illustrationshowing the cation segregation and phase separation process of perovskite underenvironmental stress. The effects of humidity and temperature on the film structurewere further evaluated. Under high humidity (80% RH), the film exhibits thesame degradation pathway as under ambient conditions but with much fasterkinetics. In contrast, thermal aging at 130 °C inducesdecomposition into PbI2 via volatilization, bypassing the cation segregation andphase separation pathway. Consequently, to isolate and systematically study the cation segregationand phase separation phenomenon, all subsequent experiments were restricted toambient conditions.

02 机制：水氧从三叉晶界打开缺口

在结晶过程中，NOST作为两性表面活性剂：疏水烷基链朝向空气，降低溶液表面张力、促进成核；极性头基锚定晶面，疏水链形成“溶质储库”和“溶剂渗透屏障”，减缓溶质嵌入与溶剂快速蒸发，使结晶更可控。最终，NOST因分子较大被排出钙钛矿晶格，富集在晶界和上表面，既钝化缺陷，又用碳链阻挡水氧侵蚀。XRD未观察到NOST进入晶格引起的明显结构变化，EELS则确认S在晶界和上表面富集。

04 效果：薄膜更稳，器件效率与寿命双提升

Effect of cation homogenization and grain junction passivation on the performance of PSCs. aTRPL spectrum of FA_0.9Cs_0.1PbI₃films without (control)and with 0.75mg/mL NOST addition (target) (with the sample structure of Glass/ITO/ETL/perovskite), respectively.b, c TAmaps of control and target FA0_.9Cs_0.1PbI₃films, respectively. The overlapped curves are the TA spectra at a delay time of0.84 ps. dJ-V curves comparison of the champion PSCs in both cases. The blue andgreen curves correspond to devices with the composition FA_0.9Cs_0.1PbI₃, and theorange and brown curves correspond to devices with the composition((FA_0.95Cs_0.05)PbI₃)_0.975(MAPbBr₃)_0.025. estability test of control and targetFA_0.9Cs_0.1PbI₃ PSCs at themaximumpower point (MPP) biases based on the ISOS-L-1l protocol. Source data are provided as a Source Data file. f, g Low-magnificationcross-sectional HAADF-STEMimages (top panel) and corresponding EELSmappingresults for Cs-M edge (bottom panel) for the control and target PSCs after 2200 h MPP tracking, respectively. Scale bar, 500 nm.