Eppur si Muove: Proton Diffusion in Halide Perovskite Single Crystals. Issue 46 (13th October 2020)

• Record Type: Journal Article
• Authors: Ceratti, Davide Raffaele; Zohar, Arava; Kozlov, Roman; Dong, Hao; Uraltsev, Gennady; Girshevitz, Olga; Pinkas, Iddo; Avram, Liat; Hodes, Gary; Cahen, David
• Is Part Of: Advanced materials. Volume 32:Issue 46(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-10-13
• Subjects: deuteration -- halide perovskites -- ion diffusion -- proton diffusion; Materials -- Periodicals; Chemical vapor deposition -- Periodicals; 620.11
• DOI: 10.1002/adma.202002467
• Languages: English
• ISSNs: 0935-9648

Abstract

Abstract: Ion diffusion affects the optoelectronic properties of halide‐perovskites (HaPs). Until now, the fastest diffusion has been attributed to the movement of the halides, largely neglecting the contribution of protons, on the basis of computed density estimates. Here, the process of proton diffusion inside HaPs, following deuterium–hydrogen exchange and migration in MAPbI3, MAPbBr3, and FAPbBr3 single crystals, is proven through D/H NMR quantification, Raman spectroscopy, and elastic recoil detection analysis, challenging the original assumption of halide‐dominated diffusion. The results are confirmed by impedance spectroscopy, where MAPbBr3 ‐ and CsPbBr3 ‐based solar cells respond at very different frequencies. Water plays a key role in allowing the migration of protons as deuteration is not detected in its absence. The water contribution is modeled to explain and forecast its effect as a function of its concentration in the perovskite structure. These findings are of great importance as they evidence how unexpected, water‐dependent proton diffusion can be at the basis of the ≈7 orders of magnitude spread of diffusion (attributed to I − and Br − ) coefficient values, reported in the literature. The reported enhancement of the optoelectronic properties of HaP when exposed to small amounts of water may be related to the finding. Abstract : Various phenomena and techniques can be explained by ambient‐temperature ion diffusion in halide perovskites. It is shown that the really fast diffusers are protons, rather than halides, using deuterium isotope tracing in MAPbI3, MAPbBr3, and FAPbBr3, and other methods; that water is critical for proton diffusion; and that already reported results are compatible with this new insight.