  Organic-inorganic perovskite as a promising candidate for solar energy
harvesting has attracted immense interest for its low-cost preparation and
extremely high quantum efficiency. However, the fundamental understanding of
the photophysics in perovskite remains elusive. In this work, we have revealed
two distinct states in MAPbI3 thin films at low temperature through
time-resolved photoluminescence spectroscopy (TRPL). In particular, we observe
a photo-induced carrier injection from the high energy (HE) state to the low
energy (LE) state which has a longer lifetime. The strong interaction between
the two states, evidenced by the injection kinetics, can be sensitively
controlled through the excitation power. Understanding the interacting
two-states not only sheds light on the long PL lifetime in perovskite but also
helps to understand the different behavior of perovskite in response to
different excitation power. Further efforts in modifying the low energy state
could significantly improve the quantum efficiency and lead to novel
application in optoelectronics based on perovskite.
