SOLID-STATE NMR STUDY OF MULTIPLE-CATION LEAD MIXED-ALIDE PEROVSKITE WITH HIGH EFFICIENCY.

Hybrid organic-inorganic metal-halide perovskites have emerged as highly interesting materials for various applications, such as thin-film photovoltaics or light-emitting devices, due to their outstanding optoelectronics properties. A main advantage of these materials is their tunability. Their macroscopic properties are intrinsically related to their microscopic features (i.e. atomic and molecular organization and dynamics), so mixtures of different cations and anions can be used to tune the optoelectronic properties and to enhance efficiencies and stabilities. Their promising properties have brought about an increased effort in the research of these materials. Starting from methylammonium lead iodide (MAPbI3), the archetypical hybrid halide perovskite material, several variations to the hybrid perovskite structure have been tested. In particular, the use of mixed-ion structures, in which the compositional complexity is increased by introducing dopants into the perovskite structure, has resulted in a remarkable improvement in perovskite solar cell performance. Thus, since their first use as sensitizers for solar cells in 2009 [1], perovskite solar cells have developed rapidly, achieving high power conversion efficiencies (well above 20%) and improved stability. Some of the latest top efficiencies have been reached by multiple-cation lead mixed-halide perovskites (Cs,FA,MA)Pb(I,Br)3 [2][3][4]. However, the role of the dopants and additives in the high performance of the perovskite solar cells has not been fully understood yet, and its transferability to other perovskites is not straightforward. For this reason, it is important to be able to gain atomic-level understanding of these materials. Solid-State NMR (SSNMR) spectroscopy is strongly sensitive to the local chemical environment, and as such, it proved to be a perfectly suited technique to investigate mixed perovskites. In this study, we focused on the perovskite with formula Cs0.05FA0.81MA0.14PbI2.55Br0.45 because of its high performance. We investigated it by means of SSNMR for the first time, with MAPbI3 being used a reference compound. 207Pb, 13C and 1H high-resolution SSNMR experiments allowed us to characterize the structure and composition of the samples, highlighting phase homogeneity and/or segregation, and to investigate ion dynamics by exploiting both spectral and relaxation properties. References: [1] A. Kojima, K. Teshima, Y. Shirai, T. Miyasaka, J. Am. Chem. Soc., 131, 6050-6051 (2009). [2] M. Saliba, T. Matsui, J.-Y. Seo, K. Domanski, J.-P. Correa-Baena, M. K. Nazeeruddin, S. M. Zakeeruddin, W. Tress, A. Abate, A. Hagfeldtd, M. Grätzel, Energy Environ. Sci., 9, 1989-1997 (2016). [3] Y. Sun, J. Peng, Y. Chen, Y. Yao, Z. Liang, Sci. Rep., 7, 46193 (2017). [4] T. J. Jacobsson, S. Svanström, V. Andrei, J. P. H. Rivett, N. Kornienko, B. Philippe, U. B. Cappel, H. Rensmo, F. Deschler, G. Boschloo1, J. Phys. Chem. C., 122, 25, 13548-13557 (2018).