Abstract
Time-correlated single photon counting has been conducted to gain further insights into the short photoluminescence lifetimes (nanosecond) of lead iodide perovskite (MAPbI3) thin films (∼100 nm). We analyze three different morphologies, compact layer, isolated island, and connected large grain films, from 14 to 300 K using a laser excitation power of 370 nJ/cm2. Lifetime fittings from the Generalized Berberan-Santos decay model range from 0.5 to 6.5 ns, pointing to quasi-direct bandgap emission despite the three different sample strains. The high energy band emission for the isolated-island morphology shows fast recombination rate centers up to 4.8 ns–1, compared to the less than 2 ns–1 for the other two morphologies, similar to that expected in a good quality single crystal of MAPbI3. Low-temperature measurements on samples reflect a huge oscillator strength in this material where the free exciton recombination dominates, explaining the fast lifetimes, the low thermal excitation, and the thermal escape obtained.
Highlights
IntroductionSince long lifetimes often indicate materials with long diffusion lengths (L = D·τ ), one of the main intensively explored topics is the preservation of carrier diffusion length in perovskite materials.[21−26] It has been shown that the lead iodide perovskite film has a diffusion length about two times longer than that of the lead bromide perovskite film.[21] Even between the same perovskite material, the diffusion length depends on the sample preparation method,[21] as each deposition/growth method comes with some characteristic defects in a microscale
The long carrier lifetime (τ) measured in perovskites is not complete understood if we assume them to be direct bandgap semiconductors with efficient absorption.[14−20] That is to say, there is a contradictory behavior in the properties that the perovskites exhibit if we consider that the absorption and emission of photons are ruled by the same transition matrix element
In order to get further insights into short photoluminescence lifetimes, we have investigated the dynamics of the recombination pathways of the same material in three different morphologies of lead iodide perovskites films at different temperatures ranging from 14 to 300 K and at a laser excitation power of 370 nJ/cm[2]
Summary
Since long lifetimes often indicate materials with long diffusion lengths (L = D·τ ), one of the main intensively explored topics is the preservation of carrier diffusion length in perovskite materials.[21−26] It has been shown that the lead iodide perovskite film has a diffusion length about two times longer than that of the lead bromide perovskite film.[21] Even between the same perovskite material, the diffusion length depends on the sample preparation method,[21] as each deposition/growth method comes with some characteristic defects in a microscale. For routing testing of the carrier diffusion length, a laser grating technique has been proposed, instead of joint measurements of mobility and photoluminescence lifetime.[21]
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