Investigation of Threshold Carrier Densities in the Optically Pumped Amplified Spontaneous Emission of Formamidinium Lead Bromide Perovskite Using Different Excitation Wavelengths

The high crystal quality of formamidium lead bromide perovskite (CH(NH2)2PbBr3 = FAPbBr3) was infiltrated in a mesoporous TiO2 network. Then, high-quality FAPbBr3 films were evaluated as active lasing media, and were irradiated with a picosecond pulsed laser to demonstrate amplified spontaneous emission (ASE), which is a better benchmark of its intrinsic suitability for gain applications. The behavior was investigated using two excitation wavelengths of 440 nm and 500 nm. Due to the wavelength-dependent absorbance spectrum and the presence of a surface adsorption layer that could be reduced using the shorter 440 nm wavelength, the ASE power dependence was strongly reliant on the excitation wavelength. The ASE state was achieved with a threshold energy density of ~200 µJ/cm2 under 440 nm excitation. Excitation at 500 nm, on the other hand, needed a higher threshold energy density of ~255 µJ/cm2. The ASE threshold carrier density, on the other hand, was expected to be ~4.5 × 1018 cm−3 for both excitations. A redshift of the ASE peak was detected as bandgap renormalization (BGR), and a BGR constant of ~5–7 × 10−9 eV cm was obtained