Restraining effect of film thickness on the behaviour of amplified spontaneous emission from methylammonium lead iodide perovskite

The authors report amplified spontaneous emission (ASE) behaviour from methylammonium lead iodide (CH3NH3PbI3) perovskite films of different thicknesses. The ASE threshold carrier density noticeably decreased with thickness, indicating the existence of different traps with perovskite films of smaller thicknesses. We attribute this behaviour to the presence of surface states, whose origin can result from different practical fabrication steps with samples of small thicknesses. The ASE threshold carrier density increased from 3.29 × 1018 cm−3 at a film thickness of 650 nm to 7.73 × 1018 cm−3 at a film thickness of 80 nm. This work warns that while decreasing the film thickness is of practical importance to reduce the ASE threshold pump current, e.g. in electrically driven light-emitting diodes, the solution processing of perovskites, newly re-discovered for their potential photonic and photovoltaic applications, can be a restraining factor. Band gap renormalisation (BGR) is also observed in the prepared films as a redshift in the ASE peak with increasing the pump power, and the BGR coefficient is estimated to be ∼ 6.3 × 10−8 eV cm.