Femtosecond Time-Resolved Transient Absorption Spectroscopy of CH₃NH₃PbI₃ Perovskite Films: Evidence for Passivation Effect of PbI₂

Abstract

CH3NH3PbI3 perovskite layered films deposited on substrates with and without a titania support structure have been prepared and studied using time-resolved femtosecond transient absorption (fs-TA) spectroscopy in the visible light range (450-800 nm). The electron injection dynamics from the photoexcited perovskite layers to the neighboring film structures could be directly monitored via the transient bleaching dynamics of the perovskite at ∼750 nm and thus systematically studied as a function of the layer-by-layer architecture. In addition, for the first time we could spectrally distinguish transient bleaching at ∼750 nm from laser-induced fluorescence that occurs red-shifted at ∼780 nm. We show that an additional bleach feature at ∼510 nm appears when PbI2 is present in the perovskite film. The amplitudes of the PbI2 and perovskite TA peaks were compared to estimate relative amounts of PbI2 in the samples. Kinetic analysis reveals that perovskite films with less PbI2 show faster relaxation rates than those containing more PbI2. These fast dynamics are attributed to charge carrier trapping at perovskite grain boundaries, and the slower dynamics in samples containing PbI2 are due to a passivation effect, in line with other recently reported work.

Investigation of moisture stability and PL characteristics of terpineol-passivated organic–inorganic hybrid perovskite

“…The sample stored at 50 % humidity for 30 days shows the evidence of degradation in the XRD and this leads to the formation of PbI 2 on the surface of the perovskite grains. PbI 2 has been shown to act as a passivating layer that can prolong charge carrier recombination [23]. Here, we find that the lifetime is extended from 15 to 36 ns when PbI 2 is present in the film.…”

“…Recent published work [23] has also confirmed that PbI 2 with a bulk band gap of 2.3 eV can form a passivation layer in the unfilled grain boundaries of perovskite films. The slower injection rate and longer recombination times of photoinduced charge carriers demonstrate the effect of passivation.…”

Efficient Semitransparent Perovskite Solar Cells Using a Transparent Silver Electrode and Four-Terminal Perovskite/Silicon Tandem Device Exploration

“…Also in Figure 2(b), the XRD diffraction peaks around 14.21°, 28.51°, and 31.88°are assigned to the (110), (220), and (310) lattice planes, respectively, of the tetragonal perovskite structure, which indicates the formation of perovskite film. The XRD peak at 12.7°is corresponding to the cubic PbI 2 [40,41]; this is a very typical observation for the incomplete conversion into the photoactive black phase in the mixed perovskite composition. Based on the high-quality perovskite film and four-terminal architecture, the performance of fabricated devices are discussed as follows.…”

Interface Engineering for Highly Efficient and Stable Planar p‐i‐n Perovskite Solar Cells

“…However, some works demonstrated that the remaining PbI 2 at interface may slow the charge extraction process. [81] The surface modification was developed as an efficient method to promote the ultrafast interfacial charge extraction. [82][83][84][85][86] In one of our former works, we used carbon quantum dots, which acted as superfast electron tunnel, to modify the interface between ETM and perovskite, resulting in an accelerated charge extraction process which increased the extraction rate from ≈300 ps to just around 100 ps.…”