The highest efficiency Perovskite Solar Cells (PSC) contain several cations as well as a mixture of bromide and iodide anions. As well a higher efficiency, mixed cation devices show higher reproducibility and stability compared to the archetypal methyl ammonium lead iodide (MAPI). We have investigated the reasons behind these improvements in stability and efficiency by carrying out systematic studies of the effect of cation and anion substitution in PSC.<br/>In the first study we substituted 5% of seven different sized cations, from rubidium to guanidinium into methyl ammonium lead iodide (MAPI). We chose 5% substitution as all the materials showed the same crystal structure, the same band gap, and no 2D perovskite phases were formed. This allowed us to make a direct comparison between our results and understand the large changes in material and device properties introduced by some of the cations. Three of the partially substituted MAPI powders were studied by muon spectroscopy (μ-SR). We have shown that with μ-SR it is possible to detect both cation dynamics and iodide motion in perovskite materials and we have extended the technique to multi-cation systems. We also prepared inverted cells containing the different perovskite materials and compared them using a range of characterisation techniques, including impedance spectroscopy. The results are striking, confirming that all of the cations have an effect at just 5% substitution, while some of the cations substantially change the fundamental properties of the perovskite itself.<br/>In a second study we looked at bromide substitution into MAPI, the results are again striking. Just a few % of bromide impacts strongly on ion motion in the perovskite itself and substantially changes the measured impedance response of our devices.<br/>In this talk I will present our latest experimental results and discuss the implications for the performance of PSC.

Understanding the effects of cation and anion substitution on perovskite solar cells

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.