Microcavity exciton-polaritons are bosonic quasiparticles that result from the hybridization of excitons and modes of a confined electromagnetic field in a regime known as strong light-matter coupling. Having a low effective mass, polaritons can undergo condensation, the macroscopic occupation of the lowest energy and momentum state. Two-dimensional (2D) perovskites are promising candidates for polariton condensation due to their high exciton binding energies, low non-radiative recombination rates and strong oscillator strengths. However, despite their optimal optoelectronic properties, there are no reports of room temperature polariton condensation in 2D perovskites and only one unreproduced report at low temperature. In this study, we systematically examine the interplay between the emission from the exciton reservoir and the population of the lower polariton. We gain insights on how the spectral features of the emission of 2D perovskites affect polariton relaxation and onto one of the mechanisms making polariton condensation challenging in 2D perovskites.
Conjugated hairy-rod polymers, which have emerged as promising photocathode materials for solar-fuel production, are comprised of stiff, low-entropy backbones and complex side-chain substitutions, which collectively affect assembly compared to flexible-chain materials. Here, we unravel the relationship between structural and electronic disorder in a model hairy-rod polymer, PBTTT. We identify a narrow electronic density-of-states (DOS) distribution with weak spatial variations in PBTTT, while the prototypical flexible-chain polymer, P3HT, features an energetically broad, spatially variable DOS. We assign this observation to the fact that PBTTT is structurally homogeneous due to its liquid-crystalline-like behavior, contrary to the structurally heterogeneous, semi-crystalline P3HT. This view is further supported by 2D electronic spectroscopy, which reveals that PBTTT features dynamic electronic disorder, vs. P3HT, which exhibits primarily static electronic disorder. Collectively, our work provides understanding into the disordered energy landscape in conjugated hairy-rod polymers, towards accelerated materials discovery for renewable energy technologies.
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