Intrinsic Formamidinium Tin Iodide Nanocrystals by Suppressing the Sn(IV) Impurities
Dmitry N. Dirin, Anna Vivani, Marios Zacharias, Taras V. Sekh, Ihor Cherniukh, Sergii Yakunin, Federica Bertolotti, Marcel Aebli, Richard D. Schaller, Alexander Wieczorek, Sebastian Siol, Claudia Cancellieri, Lars P. H. Jeurgens, Norberto Masciocchi, Antonietta Guagliardi, Laurent Pédesseau, Jacky Even, Maksym V. Kovalenko, Maryna I. Bodnarchuk
Abstract
High Resolution Image Download MS PowerPoint Slide The long search for nontoxic alternatives to lead halide perovskites (LHPs) has shown that some compelling properties of LHPs, such as low effective masses of carriers, can only be attained in their closest Sn(II) and Ge(II) analogues, despite their tendency toward oxidation. Judicious choice of chemistry allowed formamidinium tin iodide (FASnI 3 ) to reach a power conversion efficiency of 14.81% in photovoltaic devices. This progress motivated us to develop a synthesis of colloidal FASnI 3 NCs with a concentration of Sn(IV) reduced to an insignificant level and to probe their intrinsic structural and optical properties. Intrinsic FASnI 3 NCs exhibit unusually low absorption coefficients of 4 × 10 3 cm –1 at the first excitonic transition, a 190 meV increase of the band gap as compared to the bulk material, and a lack of excitonic resonances. These features are attributed to a highly disordered lattice, distinct from the bulk FASnI 3 as supported by structural characterizations and first-principles calculations.