Light-Induced Passivation in Triple Cation Mixed Halide Perovskites: Interplay between Transport Properties and Surface Chemistry

Abstract

Mixed halide perovskites have attracted a strong interest in the photovoltaic community as a result of their high power conversion efficiency and the solid opportunity to realize low-cost and industry-scalable technology. Light soaking represents one of the most promising approaches to reduce non-radiative recombination processes and thus to optimize device performances. Here, we investigate the effects of 1 sun illumination on state-of-the-art triple cation halide perovskite thin films Cs0.05(MA0.14, FA0.86)0.95 Pb (I0.84, Br0.16)3 by a combined optical and chemical characterization. Competitive passivation and degradation effects on perovskite transport properties have been analyzed by spectrally and time-resolved quantitative imaging luminescence analysis and by X-ray photoemission spectroscopy (XPS). We notice a clear improvement of the optoelectronic properties of the material, with a increase of the quasi fermi level splitting and a corresponding decrease of methylammonium MA+ for short (up to 1 h) light soaking time. However, after 5 h of light soaking, phase segregation and in-depth oxygen penetration lead to a decrease of the charge mobility.

Effects of Crystal Morphology on the Hot-Carrier Dynamics in Mixed-Cation Hybrid Lead Halide Perovskites

“…Figure 2b shows the false-color map of the absorbance difference ∆A (expressed in mOD) as a function of the probe energy (y axis) and the pump-probe time delay between (x axis) obtained for the Meso-Capping sample with E p = 2.25 eV impinging on the Meso side with a fluence of 4.00 µJ/cm 2 that corresponds to an initial carrier density of about 8.00 × 10 16 cm −3 . The TA map presents a negative signal at 1.66 eV assigned to the photobleaching (PB) of the CsMAFA band gap [39][40][41], in agreement with the absorption spectrum acquired with an ultraviolet-visible (UV-Vis) spectrophotometer (Jasco V-630) and reported in the inset of Figure 2b. In similar experiments performed on the more widely studied MAPI, the weak and broad positive large band of photoinduced absorption (PIA) in the 1.75 to 1.90 eV range is typically assigned to band gap renormalization effects [22] and population of newly excited states induced by the pump [42].…”

One‐Step Slot‐Die Coating Deposition of Wide‐Bandgap Perovskite Absorber for Highly Efficient Solar Cells

“…From the transmission curves, no noticeable variation of the optical bandgap value can be observed. This is confirmed by the constant bandgap value of 1.64 eV obtained from the fitting of the photoluminescence (PL) curves, using the model proposed by Katahara et al [42,43] (Figure 4b). High-resolution cathodoluminescence (CL) mappings, that allow to acquire an emission spectrum on every location of the sample surface with a spatial resolution below 100 nm, were conducted on the three samples.…”

Mapping Transport Properties of Halide Perovskites via Short-Time-Dynamics Scaling Laws and Subnanosecond-Time-Resolution Imaging

“…INTRODUCTIONOver the last decade, lead-halide perovskites solar cells have proved to be a serious candidate for reaching large scale photovoltaic (PV) solar energy conversion, a much-needed solution to meet climate targets and move towards a low-carbon economy. However, despite this emerging technology has recently reached a record power conversion efficiency of 25.5% for a single junction device [1,2], several open questions persist in the scientific community, ranging from the nature and densities of the defects in the absorbers [3-5], the optimal design for the interfaces energetics in a full device [6,7], and the long term stability [7][8][9].The optimization of device performances goes along with the complete understanding of complex recombination processes occurring both in the bulk and at the interfaces. Due to the interplay of several chemical and physical parameters in these hybrid compounds, such…”