Colloidal Synthesis of Air-Stable Alloyed CsSn 1-x Pb x I 3 Perovskite Nanocrystals for Use in Solar Cells.

Organic-inorganic hybrid perovskite solar cells have demonstrated unprecedented high power conversion efficiencies in the past few years. Now, the universal instability of the perovskites has become the main barrier for this kind of solar cells to realize commercialization. This situation can be even worse for those tin-based perovskites, especially for CsSnI ₃ , because upon exposure to ambient atmosphere the desired black orthorhombic phase CsSnI ₃ would promptly lose single crystallinity and degrade to the inactive yellow phase, followed by irreversible oxidation into metallic Cs ₂ SnI ₆ . By alloying CsSnI ₃ with CsPbI ₃ , we herein report the synthesis of alloyed perovskite quantum dot (QD), CsSn _1-x Pb _x I ₃ , which not only can be phase-stable for months in purified colloidal solution but also remains intact even directly exposed to ambient air, far superior to both of its parent CsSnI ₃ and CsPbI ₃ QDs. Ultrafast transient absorption spectroscopy studies reveal that the photoexcited electrons in the alloyed QDs can be injected into TiO ₂ nanocrystals at a fast rate of 1.12 × 10 ¹¹ s ^-1 , which enables a high photocurrent generation in solar cells.