Ten years ago, the hybrid organic-inorganic halide perovskites have emerged in the framework of photovoltaics. But these materials present also relevant physical properties for light emitting devices as suggested more than 20 years ago by pioneer works [1-3]. In particular, just by tuning their composition and/or dimensionality, it is possible to tune easily the band gap and the excitonic properties of this new class of semiconductors. Moreover, these materials can be solution processed and deposited in large surface which is suitable for wide scale wafers and devices, representing a great hope for obtaining large –surface and low-cost emitting devices.

Here, we will focus our attention on perovskites emitting in the green range, addressing the problem of the green gap for lasers and we will study the light-matter interaction in one-dimensional planar microcavities containing them.

A lot of efforts have been done to embed 2D layered perovskites, presenting the electronic structure of a multi-quantum well, in the cavities. Due to very large excitonic effects, the strong coupling regime between the photon mode of the Fabry-Perot cavity and the excitonic mode of the perovskite is obtained at room temperature even with a low quality factor [3]. This leads to the formation of the so-called polaritons, which are a linear and coherent superposition of the exciton and photon states. Nevertheless, it seems difficult to obtain the condensation of these polaritons. Moreover, the transport properties of the 2D perovskites are highly asymmetric due to their layered structure.

We will consider then a microcavity containing a large-surface spin coated thin film of the 3D perovskite CH₃NH₃PbBr₃ as the optical active material. Here again, we show, from both reflectivity and photoluminescence experiments, the strong coupling regime between the photon mode of the Fabry-Perot cavity and the excitonic mode of the perovskite at room temperature [4]. By increasing the incident power, we demonstrate a random lasing emission in the green occurring in the microcavity which is directionally filtered by the lower polariton dispersion curve [5]. In this case, the angle of emission can be controlled by changing the microcavity detuning. Angles of emission as large as 22° are experimentally obtained. This result is interesting from a fundamental point of view because it combines two intriguing physical phenomena: the cavity exciton-polariton and the random lasing, and from a more applied point of view: the control of the random lasing emission direction is a crucial point for optoelectronic applications, such as the LIDAR technology for example.

These works open the route to fundamental studies on the Bose-Einstein condensation of polaritons and to new large-surface opto-electronic devices based on polaritonic effects, working at room temperature, potentially electrically injectable as 3D hybrid perovskites present good transport properties. As perspectives, other configurations, such as nanoimprinted exciton-polariton metasurfaces, are currently being developed to obtain cost-effective and large-scale polaritonic devices operating at room temperature [6].