Abstract |
Mixed halide perovskites are ideal materials for tandem solar cells (solar energy conversion), but they suffer from detrimental light-induced phase segregation, which can affect their optoelectronic performance. In the course of this thesis, the light-induced phase segregation in a FA0.5MA0.5Pb(I0.5Br0.5)3 thin perovskite film was investigated. Specifically, the time evolution of the emission spectra was studied at different laser irradiation conditions, such as excitation intensity (>1 W/cm2 ) and irradiation time. Optical spectroscopy measurements revealed the co-existence of three perovskite phases, a mixed halide phase, a bromide-rich phase, and an iodide-rich phase within the film, due to the phase segregation effect under light excitation. It was observed that at short irradiation times the photoluminescence (PL) from the iodiderich phase dominated the PL spectra, while at long irradiation times its PL was significantly reduced and the PL from the bromide-rich phase was intensified. These variations in PL intensity at different irradiation times could be explained by effects such as, the accumulation of charge carriers at the potential minimum (the lowest energy gap), PL quenching and band filling. The light-induced phase segregation of FA0.5MA0.5Pb(I0.5Br0.5)3perovskite was found to be suppressed, compared to other perovskite materials such as MAPb(I0.5Br0.5)3. In addition, it was found that strong PL quenching can affect the reversibility of the phase segregation, which is evidence for iodine expulsion (loss of iodine). Finally, the charge carrier recombination dynamics during phase segregation at different excitation intensities was investigated by time-resolved photoluminescence measurements.
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