In the past few years, organic–inorganic halide perovskites have rapidly emerged as promising materials for photovoltaic applications, but simultaneously achieving high performance and long-term stability has proved challenging. Here, we show a one-step solution-processing strategy using phosphonic acid ammonium additives that results in efficient perovskite solar cells with enhanced stability. We modify the surface of methylammonium lead triiodide (CH₃NH₃PbI₃) perovskite by spin-coating its precursor solution in the presence of butylphosphonic acid 4-ammonium chloride. Morphological, structural and elemental analyses show that the phosphonic acid ammonium additive acts as a crosslink between neighbouring grains in the perovskite structure, through strong hydrogen bonding of the -PO(OH)₂ and -NH₃⁺ terminal groups to the perovskite surface. The additives facilitate the incorporation of the perovskite within a mesoporous TiO₂ scaffold, as well as the growth of a uniform perovskite layer at the surface, enhancing the material's photovoltaic performance from 8.8 to 16.7% as well as its resistance to moisture.

http://www.nature.com/nchem/journal/vaop/ncurrent/full/nchem.2324.html
Nature Chemistry (2015) doi:10.1038/nchem.2324

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Perovskite solar cells: Crystal crosslinking
Licheng Sun
http://www.nature.com/nchem/journal/vaop/ncurrent/full/nchem.2323.html
Nature Chemistry (2015) doi:10.1038/nchem.2323