Ultrafast Spectrally Resolved Photoinduced Complex Refractive Index Changes in CsPbBr₃ Perovskites

Abstract

The exceptional optoelectronic properties of metal halide perovskites have been illuminated by extensive spectroscopic studies. Recent measurements suggest strong photoinduced refractive index changes in these materials, which influence their functionality and obscure access to photoinduced extinction spectra from transient absorption spectroscopy, but such photorefractive effects are difficult to measure and model. Here, we use white light pulse interferometryan experimentally straightforward adaptation of transient absorption spectrosco-pyto directly probe photoinduced refractive index changes in CsPbBr 3 films and nanocrystals on ultrafast time scales. Strong photoinduced refractive index changes are spectrally resolved and used to access extinction spectra, and these intrinsic optical parameters are then used to directly resolve more accurate photoexcited carrier temperatures and bandgap renormalization, resolving ambiguities in the present literature. As well as understanding the intrinsic photoresponse of semiconductors, quantifying photoinduced refractive effects will be valuable for designing photonic devices including switches, lasers, and concentrating photovoltaics.

Hot carrier extraction in CH 3 NH 3 PbI 3 unveiled by pump-push-probe spectroscopy

“…1A) arising from ESA and not because of the photoinduced change in the refractive index (see figs. S2 and S6) ( 28 , 29 ). After re-exciting a fraction of the band-edge population at 3 ps with the push pulse, the re-excited carrier population quickly cools back to the band edge on a subpicosecond time scale of ~0.4 ps, in agreement with the literature ( 11 , 13 , 17 ).…”

Single 3.3 fs multiple plate compression light source in ultrafast transient absorption spectroscopy

“…The high spectral density of the MPC allows for experiments which were previously impossible. Three examples of measurements where this technique is valuable are materials with a high absorption coefficient 36 , frequency domain interferometry (FDI) 37 , 38 and spatial-resolved transient absorption spectroscopy 39 , 40 . Highly absorbing materials are often restricted to reflection experiments as the transmitted probe is too weak to detect.…”

Composition-tuned MAPbBr3 nanoparticles with addition of Cs+ cations for improved photoluminescence

“…Hybrid organic-inorganic lead halide perovskites (LHPs) have been widely explored for optoelectronic applications resulting in solar cells with a record power conversion efficiency (PCE) of 25.5% and light emitting diodes with an external quantum efficiency (EQE) exceeding 20%. [1][2][3][4][5][6][7] The key advantages of this class of materials are solution processability, inexpensive starting materials, composition tunable band gap, high hole and electron mobility, and high defect tolerance. 8,9 Despite showing high efficiency, prototype perovskite materials such as MAPbX 3 and FAPbX 3 (where MA ¼ methylammonium; FA ¼ formamidinium; X ¼ Br, I) suffer from phase instability, poor reproducibility, and thermal instability.…”