Abstract
Tin-halide perovskites have great potential as photovoltaic materials, but their performance is hampered by undesirable oxidation of Sn(ii) to Sn(iv). NMR proves DMSO to be a main cause of oxidation.
Highlights
Jorge Pascual, a Giuseppe Nasti,b Mahmoud H
We find that dimethylsulfoxide (DMSO), a typical solvent for Sn-based perovskites, oxidizes Sn(II) in acidic conditions under temperatures used for film annealing
We propose a redox reaction between DMSO and Sn(II), catalyzed by hydroiodic acid, with iododimethylsulfonium iodide intermediate
Summary
As we show, heating the solution containing 10 mol% SnF2 did not produce any significant change in colour, and showed no Sn(IV) signal (we investigated the complete spectral range in case new compounds were being formed) This result suggests the possibility of using certain additives to suppress or even prevent the redox reaction between DMSO and Sn(II). We found a new group of signals in 1H spectra with shifts in the range of 6.80–7.20 ppm, which were increasing in intensity over time (Fig. S9, ESI†), suggesting that they belong to compounds forming during decomposition of the solution At this point, we performed 2D-NMR experiments to understand the nature of these products. The oxidising effect of DMSO could be behind it, alternative strategies that avoid the use of this solvent have to be discovered in order to improve the performance of these devices
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