Halide perovskite photovoltaic cells have attracted tremendous attention in recent years, due to the rapid rise of their solar cell efficiencies, which have increased from 9% in 2012 to over 25% by 2019, and are now competitive with crystalline silicon (1,2). In this application note, time-resolved photoluminescence spectroscopy is shown to be a powerful tool for investigating and optimizing the behavior of perovskites through the measurement of charge carrier lifetimes.
Methyl ammonium lead iodide (MAPI) perovskite films were deposited on quartz discs, using the methylamine/acetonitrile route (3), followed by annealing at 100 °C. Photoluminescence lifetimes were measured using an Edinburgh Instruments FLS1000 photoluminescence spectrometer equipped with an EPL-405 pulsed diode laser, a PMT-900 detector, and time-correlated single photon counting (TCSPC) counting electronics.
During the fabrication of perovskite solar cells, the perovskite layer is first deposited by spin-coating, and the layer is then annealed at a high temperature to complete the film formation process. The temperature and duration of this annealing step can have a dramatic impact on the microstructure of the perovskite layer and on the efficiency of the photovoltaic cell.
The photoluminescence decays of three MAPI films fabricated with different annealing times were measured using TCSPC and fit with stretched exponential decays using the Fluoracle® software of the FLS1000 (Figure 1). As the annealing time is increased from 15 to 60 min, the mean lifetime of the photoluminescence decay was found to increase from 28 to 44 ns.
The mean lifetime of the MAPI films was measured using TCSPC with the FLS1000 photoluminescence spectrometer and was found to increase with annealing time, indicating that longer annealing extends the average charge carrier lifetime which may improve solar cell efficiency.
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