Lifer Rachel, Rafisiman Nathan, Shaek Saar, Basu Arghyadeep, Kauffmann Yaron, Pavlopoulos Nicholas G, Castelli Ivano E, Chuntonov Lev, Bekenstein Yehonadav
Department of Materials Science and Engineering, Technion - Israel Institute of Technology, 32000 Haifa, Israel.
Department of Chemistry, Technion - Israel Institute of Technology, 32000 Haifa, Israel.
Chem Mater. 2025 May 25;37(11):4178-4186. doi: 10.1021/acs.chemmater.5c00803. eCollection 2025 Jun 10.
Enhancing the efficiency and stability of lead halide perovskite devices is crucial to their practical application. Previous treatments with thiocyanate (SCN) have demonstrated significant improvements in the photoluminescence quantum yield (PLQY) and stability of CsPbBr nanocrystals (NCs), but the underlying mechanisms remain partially unresolved. Addressing the challenge of low SCN solubility in traditional nonpolar solvents, our study introduces a urea-ammonium thiocyanate (UAT)-based ionic liquid surface treatment. This method facilitates a higher SCN loading by creating a liquid-liquid interface that is compatible with the organic colloidal suspension, preventing NC degradation, and achieving near-unity PLQY. Utilizing transmission electron microscopy techniques, we present atomic resolution evidence that thiocyanate-treated surfaces are rich in sulfur and display structural dilation of the lattice spacing of 3%. This supports that thiocyanate acts as a pseudohalide and binds to Pb cations on the NC surfaces. As a result, the treated NCs show enhanced stability against ionic substitution while maintaining the perovskite structure intact. Our findings provide conclusive evidence that the primary mechanism of performance enhancement is the passivation of surface traps attributed to bromide vacancies rather than the scavenging of excess lead cation. This surface treatment method slows ion migration, a prominent challenge in photovoltaics, offering a significant advancement in the development of perovskite-based devices.
提高卤化铅钙钛矿器件的效率和稳定性对其实际应用至关重要。先前用硫氰酸盐（SCN）进行的处理已证明CsPbBr纳米晶体（NCs）的光致发光量子产率（PLQY）和稳定性有显著提高，但其潜在机制仍部分未得到解决。为应对SCN在传统非极性溶剂中溶解度低的挑战，我们的研究引入了基于尿素-硫氰酸铵（UAT）的离子液体表面处理。该方法通过创建与有机胶体悬浮液相容的液-液界面，促进了更高的SCN负载量，防止了NC降解，并实现了接近单位的PLQY。利用透射电子显微镜技术，我们提供了原子分辨率的证据，表明经硫氰酸盐处理的表面富含硫，且晶格间距显示出3%的结构扩张。这支持了硫氰酸盐作为拟卤化物并与NC表面的Pb阳离子结合的观点。结果，经处理的NCs在保持钙钛矿结构完整的同时，对离子取代表现出增强的稳定性。我们的研究结果提供了确凿的证据，表明性能增强的主要机制是钝化归因于溴空位的表面陷阱，而不是清除过量的铅阳离子。这种表面处理方法减缓了离子迁移，这是光伏领域的一个突出挑战，为基于钙钛矿的器件开发带来了重大进展。
