Single-crystal
perovskites with excellent photophysical properties
are considered to be ideal materials for optoelectronic devices, such
as lasers, light-emitting diodes and photodetectors. However, the
growth of large-scale perovskite single-crystal films (SCFs) with
high optical gain by vapor-phase epitaxy remains challenging. Herein,
we demonstrated a facile method to fabricate large-scale thin CsPbBr3 SCFs (∼300 nm) on the c-plane sapphire
substrate. High temperature is found to be the key parameter to control
low reactant concentration and sufficient surface diffusion length
for the growth of continuous CsPbBr3 SCFs. Through the
comprehensive study of the carrier dynamics, we clarify that the trapped-related
exciton recombination has the main effect under low carrier density,
while the recombination of excitons and free carriers coexist until
free carriers plays the dominate role with increasing carrier density.
Furthermore, an extremely low-threshold (∼8 μJ cm–2) amplified spontaneous emission was achieved at room
temperature due to the high optical gain up to 1255 cm–1 at a pump power of 20 times threshold (∼20 P
th). A microdisk array was prepared using a focused ion
beam etching method, and a single-mode laser was achieved on a 3 μm
diameter disk with the threshold of 1.6 μJ cm–2. Our experimental results not only present a versatile method to
fabricate large-scale SCFs of CsPbBr3 but also supply an
arena to boost the optoelectronic applications of CsPbBr3 with high performance.
Confirmation of direct photogeneration of intrinsic delocalized free carriers in small-molecule organic semiconductors has been a long-sought but unsolved issue, which is of fundamental significance to its application in photo-electric devices. Although the excitonic description of photoexcitation in these materials has been widely accepted, this concept is challenged by recently reported phenomena. Here we report observation of direct delocalized free carrier generation upon interband photoexcitation in highly crystalline zinc phthalocyanine films prepared by the weak epitaxy growth method using ultrafast spectroscopy. Transient absorption spectra spanning the visible to mid-infrared region revealed the existence of short-lived free electrons and holes with a diffusion length estimated to cross at least 11 molecules along the π−π stacking direction that subsequently localize to form charge transfer excitons. The interband transition was evidenced by ultraviolet-visible absorption, photoluminescence and electroluminescence spectroscopy. Our results suggest that delocalized free carriers photogeneration can also be achieved in organic semiconductors when the molecules are packed properly.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.