One-step mechanochemical incorporation of an insoluble cesium additive for high performance planar heterojunction solar cells

Daniel Prochowicz, Pankaj Yadav, Michael Saliba, Dominik J. Kubicki, Mohammad Mahdi Tavakoli, Shaik M. Zakeeruddin, Janusz Lewiński, Lyndon Emsley, Michael Grätzel

DOI:  10.1016/j.nanoen.2018.05.010..
First published online 5 May 2018.
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State-of-the-art cesium-containing multiple-cation perovskites are generally synthesized from stock solutions of perovskite precursors and CsI in DMSO and DMF. However, compositional diversity of multi-component perovskites is significantly hampered due to the poor solubility of other cesium halides in these solvents. Here, we show how insoluble CsCl, as a new source of cesium cation, can be integrated into a multiple-cation perovskite material by a one-step method involving grinding of the precursors. The resulting polycrystalline powder is fully soluble in a DMSO/DMF mixture and allows formation of perovskite thin films. ¹³³Cs solid-state MAS NMR data indicate that the cesium cation is almost fully (90%) incorporated into the 3D perovskite lattice, while the remaining 10% forms a cesium-rich mixed-halide secondary phase. The planar heterojunction device fabricated using this original mechanoperovskite yielded a power conversion efficiency of 19.12% and an open circuit voltage of 1.16 V. Moreover, we show that the introduction of CsCl improves both interfacial and bulk photovoltaic metrics. Our one-step approach provides an efficient general method for incorporating poorly soluble salts into multi-component perovskite crystal lattices.