The ability to efficiently convert low-intensity light between the visible and infrared would be an enabling technology—particularly for applications such as 3rd-generation photovoltaics, biological imaging, and cost-effective sensitized silicon focal plane array detectors with response in the short-wave infrared (SWIR; λ:1--3µm). Accordingly, we are advancing recent approaches that combine two excitonic materials—organic semiconductors and colloidal nanocrystals—to achieve broadband, non-coherent photon up-conversion from the SWIR to the visible.<br/><br/>To achieve upconversion, our general approach is to synthesize lead sulfide nanocrystals that are able absorb SWIR photons (λ&gt;1 µm) and funnel these excitations to sensitize the spin-triplet excited state of an organic semiconductor (e.g. rubrene). In the molecules, strong exchange-splitting allows the excitonic energy to be combined via triplet fusion to create visible light. In solid state devices, we have observed excitonic upconversion from λ=1.1μm→612nm, the threshold of the SWIR. Further, transient spectroscopy shows that there is no fundamental barrier to efficient performance of the annihilator materials at 1/10th the intensity of natural sunlight! Indeed, trials in solution with a novel emitter molecule and an standard organometallic sensitizer have achieved upconversion from λ&gt;700nm with spectrally-integrated irradiance less than 1/3rd of the AM1.5 solar standard, and offer a route to free-floating upconverting fluorophores.<br/><br/>However, although colloidal quantum dots are near-ideal SWIR sensitizers—their photoexcitations are functionally spin-mixed at room temperature, and their optical gap can be tuned during colloidal synthesis—we now must advance our understanding of materials, device architectures, and photophysical dynamics to enable wide application of this hybrid approach to excitonic photon conversion. Indeed, our recent work indicates that process additives offer facile size-tuning of small (excitonic peak: λ&lt;1.1µm) PbS nanocrystals, as well as insight into the underlying growth mechanism

Progress using hybrid nanomaterials for excitonic photon upconversion

2019 Fall National Meeting

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