Ultralow absorption coefficient and temperature dependence of radiative recombination of CH₃NH₃PbI₃ perovskite from photoluminescence

Spectrally resolved photoluminescence is used to measure the band-to-band absorption coefficient α_BB(ω) of organic-inorganic hybrid perovskite methylammonium lead iodide (CH₃NH₃PbI₃) films from 675 to 1400 nm. Unlike other methods used to extract the absorption coefficient, photoluminescence is only affected by band-to-band absorption and is capable of detecting absorption events at very low energy levels. Absorption coefficients as low as 10^-14 cm^-1 are detected at room temperature for long wavelengths, which is 14 orders of magnitude lower than reported values at shorter wavelengths. The temperature dependence of α_BB(ω) is calculated from the photoluminescence spectra of CH₃NH₃PbI₃ in the temperature range 80-360 K. Based on the temperature-dependent α_BB(ω), the product of the radiative recombination coefficient and square of the intrinsic carrier density, B(T) × ni², is also obtained.