RESUMEN
Strong coupling between lead halide perovskite materials and optical resonators enables both polaritonic control of the photophysical properties of these emerging semiconductors and the observation of fundamental physical phenomena. However, the difficulty in achieving optical-quality perovskite quantum dot (PQD) films showing well-defined excitonic transitions has prevented the study of strong light-matter coupling in these materials, central to the field of optoelectronics. Herein we demonstrate the formation at room temperature of multiple cavity exciton-polaritons in metallic resonators embedding highly transparent Cesium Lead Bromide quantum dot (CsPbBr3-QD) solids, revealed by a significant reconfiguration of the absorption and emission properties of the system. Our results indicate that the effects of biexciton interaction or large polaron formation, frequently invoked to explain the properties of PQDs, are seemingly absent or compensated by other more conspicuous effects in the CsPbBr3-QD optical cavity. We observe that strong coupling enables a significant reduction of the photoemission line width, as well as the ultrafast modulation of the optical absorption, controllable by means of the excitation fluence. We find that the interplay of the polariton states with the large dark state reservoir plays a decisive role in determining the dynamics of the emission and transient absorption properties of the hybridized light-quantum dot solid system. Our results should serve as the basis for future investigations of PQD solids as polaritonic materials.
RESUMEN
The recent development of organic polaritonic solar cells, in which sunlight absorbers and photon modes of a resonator are hybridized as a result of their strong coupling, has revealed the potential this interaction offers to control and enhance the performance of these devices. In this approach, the photovoltaic cell is built in such a way that it also behaves as an optical cavity supporting spectrally well-defined resonances, which match the broad absorption bands of the dyes employed. Herein we focus on the experimental and theoretical analysis of the specific spectral and angular optical absorption characteristics of a broadband light harvester, namely a subphthalocyanine, when operating in the ultrastrong coupling regime. We discuss the implications of having a broad distribution of oscillator strengths and demonstrate that rational design of the layered structure is needed to optimize both the spectral and the angular response of the sunlight harvester dye.