  It is thought that growing large, oriented grains of perovskite can lead to
more efficient devices. We study MAPbI3 films fabricated via Flash Infrared
Annealing (FIRA) consisting of highly oriented, large grains. Domains observed
in the SEM are often misidentified with crystallographic grains, but SEM images
don't provide diffraction information. We measure the grain size, crystal
structure and grain orientation using Electron Back-Scattered Diffraction
(EBSD) and we study how these affect the optoelectronic properties as
characterized by local photoluminescence (PL) and time-resolved microwave
conductivity measurements (TRMC). We find a spherulitic growth yielding large
(tens of micron), highly oriented grains along the (112) and (400) planes in
contrast to randomly oriented, smaller (400 nm) grains observed in films
fabricated via conventional antisolvent (AS) dripping. We observe a local
enhancement and shift of the photoluminescence emission at different regions of
the FIRA clusters, but these can be explained with a combination of
light-outcoupling and self-absorption. We observe no effect of crystal
orientation on the optoelectronic properties. Additionally, despite a
substantial difference in grain size between our FIRA sample and a conventional
AS sample, we find similar photoluminescence and charge carrier mobilities and
lifetime for the two films. These findings show that the optoelectronic quality
is not necessarily related to the orientation and size of crystalline domains
in perovskite films indicating that fabrication requirements may be more
relaxed for perovskites.
