  Vibrational control (VC) of photochemistry through the optical stimulation of
structural dynamics is a nascent concept only recently demonstrated for model
molecules in solution. Extending VC to state-of-the-art materials may lead to
new applications and improved performance for optoelectronic devices. Metal
halide perovskites are promising targets for VC due to their mechanical
softness and the rich array of vibrational motions of both their inorganic and
organic sublattices. Here, we demonstrate the ultrafast VC of FAPbBr3
perovskite solar cells via intramolecular vibrations of the formamidinium
cation using spectroscopic techniques based on vibrationally promoted
electronic resonance. The observed short (~300 fs) time window of VC highlights
the fast dynamics of coupling between the cation and inorganic sublattice.
First-principles modelling reveals that this coupling is mediated by hydrogen
bonds that modulate both lead halide lattice and electronic states. Cation
dynamics modulating this coupling may suppress non-radiative recombination in
perovskites, leading to photovoltaics with reduced voltage losses.
