英国剑桥大学教授Stranks, Samuel D.团队认为局部纳米级杂质相是卤化物钙钛矿中的降解位点。相关研究成果发表在2022年5月24日出版的国际学术期刊《自然》。

了解驱动新兴能源材料不稳定性的纳米级化学和结构变化对于缓解器件退化至关重要。卤化物钙钛矿光伏器件的功率转换效率在单结和串联钙钛矿/硅电池中分别达到25.7%和29.8%，但在连续操作下仍无法保持这种性能。

该文中，研究人员开发了一个多模式显微镜工具包，以揭示在主要的富甲脒钙钛矿吸收体中，纳米级杂质相（包括六方多型和碘化铅夹杂物）不仅是光激发载流子的陷阱，其本身会降低性能，而且通过相同的陷阱过程，是吸收层光化学降解的种子。研究人员观察了与陷阱团簇相关的杂质相的光照诱导结构变化，揭示了即使是微量的这些相，而且无法通过批量测量检测到，也会影响器件寿命。这些不需要的夹杂相的类型和分布取决于薄膜的组成和加工，而多型夹杂的存在对薄膜的光稳定性最为不利。

重要的是，研究人员揭示了性能损失和固有降解过程都可以通过调节这些杂质相缺陷来缓解，并证明这需要仔细调整局部结构和化学性质。这种将束敏能源材料的纳米级结构关联起来的多模式工作流程将适用于广泛的半导体，其性能和操作稳定性的局部情况尚未建立。

附：英文原文

Title: Local Nanoscale Phase Impurities are Degradation Sites in Halide Perovskites

Author: Macpherson, Stuart, Doherty, Tiarnan A. S., Winchester, Andrew J., Kosar, Sofiia, Johnstone, Duncan N., Chiang, Yu-Hsien, Galkowski, Krzystof, Anaya, Miguel, Frohna, Kyle, Iqbal, Affan N., Nagane, Satyawan, Roose, Bart, Andaji-Garmaroudi, Zahra, Orr, Kieran W. P., Parker, Julia E., Midgley, Paul A., Dani, Keshav M., Stranks, Samuel D.

Issue&Volume: 2022-05-24

Abstract: Understanding the nanoscopic chemical and structural changes that drive instabilities in emerging energy materials is essential for mitigating device degradation. The power conversion efficiency of halide perovskite photovoltaic devices has reached 25.7% in single junction and 29.8% in tandem perovskite/silicon cells1,2, yet retaining such performance under continuous operation has remained elusive3. Here, we develop a multimodal microscopy toolkit to reveal that in leading formamidinium-rich perovskite absorbers, nanoscale phase impurities including hexagonal polytype and lead iodide inclusions are not only traps for photo-excited carriers which themselves reduce performance4,5, but via the same trapping process are sites at which photochemical degradation of the absorber layer is seeded. We visualise illumination-induced structural changes at phase impurities associated with trap clusters, revealing that even trace amounts of these phases, otherwise undetected with bulk measurements, compromise device longevity. The type and distribution of these unwanted phase inclusions depends on film composition and processing, with the presence of polytypes being most detrimental for film photo-stability. Importantly, we reveal that performance losses and intrinsic degradation processes can both be mitigated by modulating these defective phase impurities, and demonstrate that this requires careful tuning of local structural and chemical properties. This multimodal workflow to correlate the nanoscopic landscape of beam sensitive energy materials will be applicable to a wide range of semiconductors for which a local picture of performance and operational stability has yet to be established.

DOI: 10.1038/s41586-022-04872-1

Source: https://www.nature.com/articles/s41586-022-04872-1