Chemical Pathways Connecting Lead(II) Iodide and Perovskite via Polymeric Plumbate(II) Fiber

Despite
tremendous progress in optoelectronic devices using lead
perovskite (CH3NH3+PbI3–), there has been a paucity of mechanistic information
on how photoactive micron-sized crystals of lead perovskite grow from
a mixture of a layered crystal of lead­(II) iodide and methylammonium
iodide mediated by a polar solvent, DMSO or DMF. We report here that
the whole process of the lead perovskite synthesis consists of a series
of equilibria driven by reversible solvent participation involving
a polymeric strip of plumbate­(II) oligomer as a key intermediate.
A significant finding includes quick decomposition of perovskite crystal
upon exposure to DMSO or DMF at room temperature, where the solvent
molecules act as a base to remove acidic ammonium iodide from the
perovskite crystal. This observation accounts for the difficulty in
controlling perovskite solar cell fabrication. Overall, the polar
solvent is indispensible first to degrade a 2-D sheet of crystals
of lead­(II) iodide into 1-D fibrous intermediates and then to promote
Oswald ripening of perovskite crystals. The detailed chemical information
provided here will help to rationalize the photovoltaic device studies
that have so far remained empirical and to open a new venue to a developing
field of microscale lead perovskite devices, as illustrated by fabrication
of photovoltaic devices and photodetectors.