Photo‐Excitations in Halide Perovskites: Where Do Simulations and Experiments Meet?

ABSTRACT The development of experimental methods monitoring the generation of photo‐excitations and their dynamics on the natural temporal and spatial scales of the electrons has opened up fascinating perspectives to better understand fundamental processes driven by light–matter couplings and use them to design new functional materials. This horizon, however, is shadowed by challenges related to the interpretation and rationalization of the observables. Theory can help to overcome these issues only if the available approaches – both ab initio and based on model Hamiltonians – are complementary to experiments and not merely ancillary to them. In this perspective, we present state‐of‐the‐art experimental and theoretical methods to investigate photo‐excitations and their dynamics in complex materials, taking bulk CsPbBr 3 as a prototypical example. Experimentally, we show the ability of two‐dimensional electronic spectroscopy to shed light onto the electronic and vibronic excitation landscape of this system, in particular giving access to exciton–phonon coupling mechanisms. From the theory side, we discuss the advantages and drawbacks of first‐principles calculations and effective methods based on the semiconductor Bloch equations. By unveiling strengths and bottlenecks of the presented approaches, we suggest viable strategies to make simulations and experiments finally join hands.