In the last few years, non-coherent sensitized photon up-conversion (SUC) in multi-component systems has been developed to achieve significantly high quantum yields for various chromophore combinations at low excitation powers, spanning from the ultraviolet (UV) to near infrared (NIR) spectrum. This promising photon energy management technique became indeed suitable for wide applications in lighting technology and especially in photovoltaics, being able to recover the sub-bandgap photons lost by current devices. A full and general description of the SUC photophysics will be presented, with the analysis of the parameter affecting the photon conversion quantum yield and the quantities which define the optimal working range of any SUC system, namely the threshold and saturation excitation intensity. It will be shown how these quantities depend on intrinsic photophysical properties of the moieties involved and on the SUC solid host matrix. The model proposed represents a powerful tool for evaluation of a newly proposed system, and its reliability will be discussed in respect to an optimized system with SUC yield of 0.26 ± 0.02. The results obtained will outline the research guidelines which must be pursued to optimize the SUC efficiency for its perspective technological applications.

We have analyzed the dynamics of the upconversion-induced delayed fluorescence for a model multicomponent organic system, in which high concentrations of triplet states can be sustained in steady-state conditions. At different excitation powers, two regimes have been identified depending on the main deactivation channel for the triplets, namely, the spontaneous decay and the bimolecular annihilation. The excitation power density at which triplet bimolecular annihilation becomes dominant is the threshold (I(th)) to have efficient upconversion generation. The simple equation obtained for I(th) allows us to predict the theoretical efficiency of a generic system on the basis of few parameters of the constituent molecules

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Triplet-triplet annihilation (TTA) based up-conversion is a promising strategy for light harvesting the low-energy tail of the solar spectrum with photovoltaic technologies. Here, we present a bi-component system for photon managing via TTA that allows bypassing the classical statistic limit of 2/5 in the singlet generation, achieving a near unitary conversion efficiency. This result is obtained because of the peculiar relative position of the triplet and singlet energy levels of perylene, used as up-converter and emitter. The system shows a record red-to-blue external up-conversion yield of ∼10% under an irradiance of 1 sun.

Sensitized triplet–triplet annihilation in multicomponent organic systems is already demonstrated to be suitable for obtaining efficient up‐conversion in solution with excitation power densities comparable to solar irradiance, but loses efficiency in the solid state. Here, it is demonstrated that it is possible to reduce this limitation by incorporating a standard bicomponent system in polymer nanoparticles. The confinement of all of the involved photophysical processes in a nanometer‐scale volume makes each nanoparticle a single and isolated high‐efficiency up‐converting unit. As a consequence, these dual‐dye‐loaded nanoparticles can be used to produce drop‐cast films, as well as dopants for polymeric matrices, preserving the performances of the starting moieties in solution.

To meet the world’s demands on the development of sunlight-powered renewable energy production, triplet–triplet annihilation-based photon upconversion (TTA–UC) has raised great expectations. However, an ideal highly efficient, low-power, and in-air TTA–UC has not been achieved. Here, we report a novel self-assembly approach to achieve this, which enabled highly efficient TTA–UC even in the presence of oxygen. A newly developed lipophilic 9,10-diphenylanthracene-based emitter molecule functionalized with multiple hydrogen-bonding moieties spontaneously coassembled with a triplet sensitizer in organic media, showing efficient triplet sensitization and subsequent triplet energy migration among the preorganized chromophores. This supramolecular light-harvesting system shows a high UC quantum yield of 30% optimized at low excitation power in deaerated conditions. Significantly, the UC emission largely remains even in an air-saturated solution, and this approach is facilely applicable to organogel and solid-film systems.

Optically active materials able to up‐convert the frequency of the incident radiation can be used to enhance the performance of photovoltaic and photocatalityc cells, recovering sub‐bandgap photons not directly absorbed by the devices. Actually, sensitized up‐conversion (SUC) based on multi‐component organic systems is the most promising approach for these photon energy managing processes, being efficient also at the solar irradiance. However, applications of SUC on real devices have not been yet accomplished because its conversion yield usually drops dramatically in the solid state where the low dye mobility inhibits the diffusion controlled mechanisms ruling SUC photophysics. To overcome this limit, we prepared a single‐phase elastomer (poly‐butylacrilate) doped with proper dyes (platinum (II) octaetyl‐porphyrin and 9,10‐diphenylanthracene) to fabricate an efficient photon up‐converting material. Thanks to the residual molecular diffusion provided by the soft host, and to the quenching reduction of involved metastable electronic excited‐states in a solid environment compared to a liquid one, we obtained a record SUC yield of 17% at the solid state. SUC efficiency has been studied as function of the excitation power and sample temperature, elucidating the photophysical processes at the base of the high observed yield and assessing the guidelines for the fabrication of technologically appealing low power up‐converting materials.