Scalable dip-coated Bragg mirrors for strong light–matter coupling with 2D perovskites

Abstract

The development of scalable photonic platforms capable of sustaining strong light–matter coupling remains a central challenge in optoelectronics, largely due to the reliance on vacuum-based fabrication of high-quality distributed Bragg reflectors (DBRs). Here, we demonstrate that fully solution-processed Bragg mirrors fabricated via evaporation-induced self-assembly (EISA) and dip-coating can achieve optical quality sufficient to enter the strong exciton–photon coupling regime. The mirrors, composed of alternating mesoporous SiO2 and dense TiO2 layers, exhibit a high refractive index contrast (Δn ≈ 0.8), enabled by the reduced effective index of the mesostructured silica. Importantly, this approach not only allows the fabrication of Bragg mirrors, but also provides a versatile route to engineer the refractive index through controlled mesoporosity, establishing porosity as a key design parameter for optical functionality. This enhanced contrast allows reflectance values exceeding 94% with only five bilayers, significantly reducing structural complexity compared to conventional DBRs. By integrating these mirrors into a hybrid microcavity incorporating the two-dimensional perovskite (PEA)2PbI4, we observe well-defined upper and lower polariton branches at room temperature, with a Rabi splitting of 90 meV. Angle-resolved reflectance and photoluminescence measurements are in close agreement with a coupled oscillator model and Green's function formalism. These results establish dip-coated Bragg mirrors as a viable and scalable platform for polaritonic devices, demonstrating that strong coupling can be achieved without vacuum-based fabrication, and opening a pathway towards low-cost, solution-processed photonic and optoelectronic systems.