Ultrafast Spectrally Resolved Photoinduced Complex Refractive Index Changes in CsPbBr3 Perovskites

The exceptional optoelectronic properties of metal halide perovskites have been illuminated by extensive spectroscopic studies. Recent measurements suggest strong photo induced 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 spectroscopy-to directly probe photoinduced refractive index changes in CsPbBr3 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.