Improved light outcoupling by spontaneously formed nanostructured micro-islands in perovskite films

Halide perovskites have been the hot topic of research for their unprecedented optoelectronic properties such as high photoluminescence quantum yield (PLQY)¹ and ambipolar charge transport. These properties are generally measured at the macroscopic level, but they differ significantly at micro to nano-scale. Here, we have fabricated CH₃NH₃PbBr₃ films containing nanostructured micro-islands (MIs). We have observed that the presence of MIs shows 7 fold increased photoluminescence (PL). This enhancement is due to nanostructured morphology that can also improve the outcoupling. As seen from the fluorescence microscope, PL is mostly coming from MIs. These films were characterized by hyperspectral microscopy. The PL spectrum shows ~10 nm blue shift as compared to that of untreated films. The blue shift is attributed to the increased octahedral tilting, because the MIs consists of 20-40nm sized crystals, whereas the background has ~300 nm feature size. PL spectrum can be fitted with two Gaussian functions centered at 533 nm and 540 nm respectively, which shows the inefficient funneling of excitons. However, we have seen that the MIs show photodegradation whereas background and untreated films show photoactivation.
Reference
D. Felix, et al. J. Phys. Chem. Lett 1421-1426 (2014)