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The Role of Dimethylammonium in Bandgap Modulation for Stable Halide Perovskites
journal contribution
posted on 2020-05-19, 17:06 authored by Giles E. Eperon, Kevin H. Stone, Laura E. Mundt, Tracy H. Schloemer, Severin N. Habisreutinger, Sean P. Dunfield, Laura T. Schelhas, Joseph J. Berry, David T. MooreHalide
perovskites with bandgaps of 1.70–1.85 eV are of
interest for multijunction photovoltaics. Mixing halides on the X
site of the ABX3-structured perovskite system is a common
way to reach these bandgaps, but this method introduces phase segregation
pathways, limiting photovoltage. Recently, a new strategy for increasing
the bandgap has been introduced, where cations normally too large
to fit into the lattice, but compensated by smaller cations, are substituted
on the A site. The mechanism underlying the increase of the bandgap
with this strategy remained an open question. Here, we show that by
partial substitution of the large dimethylammonium (DMA) cation at
the A site of FAxCs1–xPbIyBr3–y perovskites, a bandgap increase is observed not
only when DMA is compensated by smaller Cs cations but also when only
DMA is added, which is accompanied by an expansion of the crystal
lattice. Our experimental findings suggest that adding DMA is causing
an unexpected tilt in the perovskite octahedra, increasing the bandgap.
Efficient solar cells based on 1.73 eV DMA-incorporated materials
are extremely stable, retaining 96% of their original efficiency over
2200 h at 85 °C in the dark and 92% of their original efficiency
after operation at 60 °C for 500 h. This octahedral tilting strategy
is a promising route for attaining efficient and stable wide bandgap
perovskite solar cells.