Speaker
Description
Hybrid metal-halide perovskites have attracted considerable interest for optoelectronic applications, including radiation detection, particularly in the X-ray range. This interest is related to the combination of several favorable properties: efficient absorption of incoming radiation, good charge-carrier transport, and the presence of heavy elements, which enhance interaction with ionizing radiation. However, the presence of defects, both in the bulk and at the interfaces, remains a critical issue. These defects can act as trapping and recombination centers, leading to reduced device performance and impaired operational stability. Among the key instability mechanisms in halide perovskites, ion migration is particularly critical, as it can modify the internal electric field, induce hysteresis, and accelerate degradation.
In this work, FAMAPI-based structures with different interlayers were investigated, with the aim of evaluating their effect on active defects at the interface. A reference sample, consisting only of the perovskite, was compared with four samples containing different transport layers: two HTLs, TaTm and Meo-2PACz, and two ETLs, C60 and C60/SnO₂. The analysis was carried out using Photo-Induced Current Transient Spectroscopy, PICTS, which is based on the measurement of photoinduced current transients as a function of temperature, to extract the activation energies of the defects. This technique also makes possible to identify slower contributions, potentially associated with the diffusion or migration of ionic species. The results show that the nature of the interlayer clearly modifies the transient response. In the reference sample, three trap levels were identified, T1, T2, and T3, with activation energies of 0.30 eV, 0.39 eV, and 0.82 eV, respectively. These were preliminarily attributed to iodine vacancies, surface defects related to undercoordinated Pb and iodine interstitials. In the samples with ETLs, dominated by the perovskite/C60 interface, only T3 remains clearly visible, while T1 and T2 appear to be passivated. For the HTL-based samples, different behaviors are observed depending on the interlayer. The MeO-2PACz sample shows only T1 and T3, indicating a possible passivation of T2, whereas the TaTm-based sample retains all three defect levels.
Overall, these results confirm that PICTS is a valuable method to investigate defect activity in FAMAPI-based structures, and the role of interlayers in controlling the and improving both the optoelectronic performance and stability of the material.