RhoBAST is a novel fluorescence light-up RNA aptamer (FLAP) that transiently binds a fluorogenic rhodamine dye. Fast dye association and dissociation result in intermittent fluorescence emission, facilitating single-molecule localization microscopy (SMLM) with an image resolution not limited by photobleaching. We demonstrate RhoBAST's excellent properties as a RNA marker by resolving subcellular and subnuclear structures of RNA in live and fixed cells by SMLM and structured illumination microscopy (SIM)..

Device fabrication methods for applications in upconversion processes using perovskite thin films have suffered from reproducibility and scalability issues, which prevent the upscaling of this technology. In this contribution, we developed a perovskite‐based upconversion device approach where the triplet annihilator is added in situ to the antisolvent and investigated the effect of the device fabrication procedure on the properties of our device. By comparing the properties of a device based on our new fabrication approach with the existing bilayer procedure, we seek to shed light on the underlying optoelectronic processes influenced by the different fabrication methods, while further advancing possible device architectures for upconversion devices. Device characterization by optical methods, X‐ray diffraction and atomic force microscopy revealed that the in situ fabricated devices match the performance or even outcompete our previously developed bilayer devices while significantly simplifying the device fabrication. In particular, we find that the developed one‐step fabrication technique enables intercalation of the upconverting layer into the perovskite film prior to annealing, resulting in a larger interface thus, more efficient charge extraction.

Photon upconversion via triplet–triplet annihilation could allow for the existing efficiency limit of single junction solar cells to be surpassed. Indeed, efficient upconversion at subsolar fluences has been realized in bulk perovskite-sensitized systems. Many questions have remained unanswered, in particular, regarding their behavior under photovoltaic operating conditions. Here, we investigate the impact of repeated and continuous illumination on bilayer perovskite/rubrene upconversion devices. We find that variations of the underlying perovskite carrier recombination dynamics greatly impact the upconversion process. Trap filling and triplet sensitization are in direct competition: more saturated trap states in the perovskite and, thus, longer underlying perovskite photoluminescence lifetimes allow for an increased number of carriers to diffuse to the perovskite/rubrene interface and undergo charge extraction to the triplet state of rubrene. As a result, the upconversion efficiency is greatly influenced by the underlying trap density: the upconverted photoluminescence intensity increases by two orders of magnitude under continuous illumination for 4 h. This shows that the upconversion efficiency is difficult to define for this system. Importantly, these results indicate that perovskite-sensitized upconversion devices exhibit peak performance under continuous illumination, which is a requirement for their successful integration into photovoltaics to help overcome the Shockley–Queisser limit in single junction solar cells.