Photoluminescence Lifetime of Perovskites on Modified Substrates

Lead halide perovskites have gained attention for their potential in optoelectronic applications, including photovoltaics and light-emitting devices, due to their remarkable optical and electronic properties. However, the performance of these materials is highly dependent on the morphological properties of underlying substrates. For instance, properties such as surface roughness and crystallinity can affect charge carrier dynamics. In this study, we investigate the effects of substrate modifications on the photoluminescence (PL) lifetimes of CsPbBr₃ perovskites deposited on TiO₂ substrates that were annealed at various temperatures ranging from room temperature to 400 °C.
The TiO₂ substrates were characterized using glancing-angle X-ray diffraction (GAXRD) and variable angle spectroscopic ellipsometry (VASE) to assess changes in crystallinity and surface roughness. Time-correlated single photon counting (TCSPC) spectroscopy was employed to measure the excitation lifetimes of the perovskites on modified substrates. SEM and X-ray diffraction were used to confirm the morphology and crystallinity of the perovskite materials.
Results showed a clear relationship between substrate annealing temperature and the PL lifetime of the perovskite microcrystals. Substrates annealed at temperatures below 300 °C exhibited increased surface roughness with increased annealing temperature (22.4 Å at room temperature and 48.05 Å at 300 °C) and correspondingly shorter PL lifetimes (3.5 ns at room temperature and 0.4 ns at 300 °C) suggesting more rapid charge carrier recombination. In contrast, substrates annealed at 350 °C exhibited the longest PL lifetimes at 4.19 ns indicating a decrease in trap-mediated non-radiative recombination. Substrates annealed at 400 °C showed a further increase in crystallinity but did not extend the lifetime beyond that seen at 350 °C, suggesting an optimal balance between surface roughness and crystallization.
These findings provide insights into the role of morphological substrate modifications in optimizing the optoelectronic properties of perovskite materials. We demonstrate that control over annealing conditions of TiO₂ substrates enables production of superior substrates with improved charge carrier behavior and extended excited state lifetimes. Such results indicate that these methods could be employed for production of high performance and extended stability of perovskite-based devices.