Kubicki Dominik J, Prochowicz Daniel, Salager Elodie, Rakhmatullin Aydar, Grey Clare P, Emsley Lyndon, Stranks Samuel D
Cavendish Laboratory, Department of Physics (CB3 0HE), University of Cambridge, JJ Thomson Avenue, Cambridge, U.K.
Department of Chemistry (CB2 1EW), University of Cambridge, Lensfield Road, Cambridge, U.K.
J Am Chem Soc. 2020 Apr 29;142(17):7813-7826. doi: 10.1021/jacs.0c00647. Epub 2020 Apr 15.
Organic-inorganic tin(II) halide perovskites have emerged as promising alternatives to lead halide perovskites in optoelectronic applications. While they suffer from considerably poorer performance and stability in comparison to their lead analogues, their performance improvements have so far largely been driven by trial and error efforts due to a critical lack of methods to probe their atomic-level microstructure. Here, we identify the challenges and devise a Sn solid-state NMR protocol for the determination of the local structure of mixed-cation and mixed-halide tin(II) halide perovskites as well as their degradation products and related phases. We establish that the longitudinal relaxation of Sn can span 6 orders of magnitude in this class of compounds, which makes judicious choice of experimental NMR parameters essential for the reliable detection of various phases. We show that Cl/Br and I/Br mixed-halide perovskites form solid alloys in any ratio, while only limited mixing is possible for I/Cl compositions. We elucidate the degradation pathways of Cs-, MA-, and FA-based tin(II) halides and show that degradation leads to highly disordered, qualitatively similar products, regardless of the A-site cation and halide. We detect the presence of metallic tin among the degradation products, which we suggest could contribute to the previously reported high conductivities in tin(II) halide perovskites. Sn NMR chemical shifts are a sensitive probe of the halide coordination environment as well as of the A-site cation composition. Finally, we use variable-temperature multifield relaxation measurements to quantify ion dynamics in MASnBr and establish activation energies for motion and show that this motion leads to spontaneous halide homogenization at room temperature whenever two different pure-halide perovskites are put in physical contact.
有机-无机卤化锡(II)钙钛矿已成为卤化铅钙钛矿在光电子应用中的有前途的替代品。虽然与铅基类似物相比,它们的性能和稳定性要差得多,但由于严重缺乏探测其原子级微观结构的方法,到目前为止,它们的性能提升很大程度上是通过反复试验实现的。在这里,我们确定了挑战,并设计了一种锡固态核磁共振协议,用于确定混合阳离子和混合卤化物卤化锡(II)钙钛矿及其降解产物和相关相的局部结构。我们发现,在这类化合物中,锡的纵向弛豫可以跨越6个数量级,这使得明智地选择实验核磁共振参数对于可靠检测各种相至关重要。我们表明,Cl/Br和I/Br混合卤化物钙钛矿可以以任何比例形成固态合金,而对于I/Cl组成,只有有限的混合是可能的。我们阐明了基于铯、甲胺和甲脒的卤化锡(II)的降解途径,并表明降解会导致高度无序、性质相似的产物,而与A位阳离子和卤化物无关。我们在降解产物中检测到金属锡的存在,我们认为这可能是之前报道的卤化锡(II)钙钛矿高电导率的原因。锡核磁共振化学位移是卤化物配位环境以及A位阳离子组成的敏感探针。最后,我们使用变温多场弛豫测量来量化MASnBr中的离子动力学,并确定运动的活化能,结果表明,只要将两种不同的纯卤化物钙钛矿物理接触,这种运动会在室温下导致卤化物自发均匀化。