Achieving the photon up-conversion thermodynamic yield upper limit by sensitized triplet–triplet annihilation

Abstract

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.

Efficient Broadband Triplet–Triplet Annihilation‐Assisted Photon Upconversion at Subsolar Irradiance in Fully Organic Systems

“…This sTTA-UC system shifts photons from the red (≈632 nm) to the blue (≈475 nm) resulting in an effective upconversion maximum QY UC of ≈33%. [ 19 ] All solutions were prepared and sealed in a glove box under nitrogen atmosphere in order to prevent quenching of the involved triplet states by molecular oxygen. Photoluminescence spectra were recorded by a nitrogen-cooled CCD coupled with a Triax-190 spectrograph (Horiba Jobin-Yvon) with a spectral resolution of 0.5 nm.…”

“…Indeed, in the high excitation regime we measured a conversion yield of QY UC = 21% for the multisensitizer system instead of the 33% reported for the model single-sensitizer solution (see Supporting Information, Figure S6). [ 19 ] This is due to a partial overlap between the lowenergy tail of the multisensitizer B -bands and the upconverted perylene photoluminescence, which induces both self-absorption and resonant back ET from the emitters to the sensitizers. By…”

“…[ 31 ] Third, its electronic structure prevents the generation of high-energy triplets upon TTA, thus maximizing the effi ciency of the annihilation step. [ 15,16,19 ] As introduced above, phosphorescent metalated porphyrins are used for TTA sensitization. [ 32 ] Thanks to the central heavymetal ion, they show fast intersystem crossing.…”

“…Then, it increases linearly with the irradiance up to the so called excitation power density threshold I th , above which it rapidly saturates to its maximum value. [ 19 ] It is evident that, for applications in the SC technologies, I th must be as low as possible and certainly below, or at least comparable, with air mass (AM) 1.5 solar irradiance. At present, this goal has only been accomplished in hybrid devices, obtained by coupling a layer of cadmium selenide fl uorescent nanocrystals that serve as a booster for the sensitizer absorption to a sTTA-UC system.…”

Recent advances in the application triplet–triplet annihilation-based photon upconversion systems to solar technologies

“…This remarkable value is not far from the maximum theoretical yield of 50% arising from the energy conservation law. 13,33 Figure 2(b) shows the gradual increment of QY uc achieved in the last 10 years. Notably, despite a slower initial development, a good performance is now assessed even for solid-state materials.…”