Highly Efficient Photon Upconversion in Self-Assembled Light-Harvesting Molecular Systems

Ogawa, Taku; Yanai, Nobuhiro; Monguzzi, Angelo; Kimizuka, Nobuo

doi:10.1038/srep10882

Cited by 160 publications

(159 citation statements)

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“…[17] TTA-upconversion (TTA-UC) quantum yield (ratio of upconverted photons to absorbed photons) of 30% was observed in solution phase. [18] This suggests that the intrinsic efficiency of the TTA-UC reaction (i.e., the being built up during the process. In Stage II, triplet excitons from a pair of emitter molecules encounter each other and they collide to form a singlet.…”

Section: Doi: 101002/adma201605987mentioning

confidence: 99%

“…To the best of our knowledge, these values are higher than that of any solid-state TTA-upconverters reported to date [9][10][11][12][13][14]19] and are comparable to some of the best TTA-UC efficiencies observed in solutionphase systems. [9][10][11][12]18] A summary of the efficiencies of solution systems [17,18,[31][32][33] is shown in Table S2 (Supporting Information). Comparisons of our devices with other solid-state TTA-UC systems [13,14,19,31,34] and other TTA-enhanced OLEDs [7,8,[35][36][37] are presented in Tables S3 and S4 (Supporting Information), respectively.…”

Section: Doi: 101002/adma201605987mentioning

confidence: 99%

“…[18] This suggests that the intrinsic efficiency of the TTA-UC reaction (i.e., the This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.…”

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Efficient Triplet Exciton Fusion in Molecularly Doped Polymer Light‐Emitting Diodes

et al. 2017

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probability of a triplet pair forming a singlet) in solution is >60%, much higher than the spin-statistical prediction of 25% (one pair of triplets collides to form one of the four states: one singlet S 1 and three triplets T 1 , assuming higher triplet and quintet states are inaccessible). Practical application of solar energy conversion requires the TTA-UC material to be in solid state rather than in solution phase. However, the TTA-UC quantum yield of solidstate systems remains low, typically below 5%, [10] and is moderately high (about 10%) in only one example. [19] To achieve high efficiencies, high excitation intensities (200 mW cm −2 or above) are commonly required. These imply that in solid state, the experimentally observed reaction efficiency of TTA-UC was up to about 20%, below the 25% spin-statistical limit.To achieve highly efficient triplet fusion (TTA-UC) in OLEDs and other TTA upconverters, we consider four criteria for the selection of emitters: (1) high fluorescence quantum yield, (2) short singlet lifetime, (3) long triplet lifetime, and (4) the energy of two triplet excitons, 2E(T 1 ) lies slightly above that of the singlet exciton, E(S 1 ), but below the second triplet state, E(T 2 ) (and also the energies of any spin-quintet states) (E(S 1 ) ≲ 2E(T 1 ) < E(T 2 )). The first and second criteria are prerequisites for efficient fluorescence. The third criterion is essential for the accumulation of a sufficiently high triplet population density required for rapid triplet-triplet collision processes. The fourth criterion ensures that higher-lying triplet or quintet states do not provide loss channels. The spin states of the triplet excitons give in principle nine spin configurations for the interacting triplet exciton pair, five associated with a quintet, three with a triplet, and one with the singlet state. It is generally considered that the quintet is always higher in energy than the initial triplet pair, so is neglected. If there are no energetically accessible higher-lying triplet states at E(T 2 ), we expect only the S 1 and T 1 excitons to form. Triplets produced from this reaction can be recycled and participate in a further fusion reaction. [7] The basic working principle of a triplet fusion LED (FuLED) is illustrated in Figure 1a. The initial stage (Stage I) of the device operation includes charge injection and exciton formation. Exciton formation on the emissive molecules may occur directly or indirectly through an additional exciton transfer step from a host material. If a host material is present, the S 1 and T 1 of the host are required to be higher than that of the emitter to allow efficient host-emitter energy transfer and to ensure long triplet lifetime of the emitter (Criterion 3 discussed above). The 25% singlet population can be converted to light emission (and nonradiative losses) from the singlet channel immediately, resulting in prompt electroluminescence (EL). The 75% triplet excitons remain nonemissive, but the population of triplets is When an organic light-emitting dio...

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Section: Doi: 101002/adma201605987mentioning

confidence: 99%

Section: Doi: 101002/adma201605987mentioning

confidence: 99%

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Efficient Triplet Exciton Fusion in Molecularly Doped Polymer Light‐Emitting Diodes

et al. 2017

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“…In this perspective, it is natural to develop triplet energy migration-based photon upconversion (TEM-UC), 10 in which triplet excitons effectively diffuse in densely organized molecular assemblies without molecular diffusion. [21][22][23][24][25][26][27][28][29][30][31][32] Among various assembly systems, molecular crystals with ordered chromophore arrangements should be promising for achieving fast TEM. However, the crystalline systems have suffered from the aggregation of donor molecules and their segregation in acceptor crystals, which caused poor TET efficiency.…”

Section: Introductionmentioning

confidence: 99%

Kinetically controlled crystal growth approach to enhance triplet energy migration-based photon upconversion

et al. 2017

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Nobuo Kimizuka, "Kinetically controlled crystal growth approach to enhance triplet energy migration-based photon upconversion," J. Photon. Energy 8(2), 022003 (2017), doi: 10.1117/1.JPE.8.022003. Abstract. Improving efficiency of triplet-triplet annihilation-based photon upconversion (TTA-UC) in crystalline media is challenging because it usually suffers from the severe aggregation of the donor (sensitizer) molecules in acceptor (emitter) crystals. We show a kinetically controlled crystal growth approach to improve donor dispersibility in acceptor crystals. As the donor-acceptor combination, a benchmark pair of platinum(II) octaethylporphyrin (PtOEP) and 9,10-diphenylanthracene (DPA) is employed. A surfactant-assisted reprecipitation technique is employed, where the concentration of the injected PtOEP-DPA solution holds the key to control dispersibility; at a higher PtOEP-DPA concentration, a rapid crystal growth results in better dispersibility of PtOEP molecules in DPA crystals. The improvement of donor dispersibility significantly enhances the TTA-UC quantum yield. Thus, the inherent function of donor-doped acceptor crystals can be maximized by controlling the crystallization kinetics.

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“…Such kinetics clearly requires the dependency of products proportional to the square of the concentration of intermediates as shown in delayed florescence intensity induced by collision of two lowest-excited triplet states [22]. Because silver atom itself is yielded from solvated electrons generated by two photon process [17], overall intensity dependence is considered to be four-photon process as shown in the following scheme.…”

Section: Resultsmentioning

confidence: 99%

Formation and Growth of Silver Nanocubes upon Nanosecond Pulsed Laser Irradiation: Effects of Laser Intensity and Irradiation Time

Qazi¹,

Shervani²,

Javaid³

et al. 2017

ANP

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Silver nanoparticles (AgNPs) were fabricated by repetitive irradiation of near ultraviolet (UV) nanosecond laser pulses (355 nm, 5 ns) in an aqueous solution of silver nitrate in the absence of stabilizing agents. A broad absorption peak was observed in the visible region showing the formation of a variety of AgNPs in the solution. Among the variety of products, it was found that silver nanocubes (AgNCs) grew in size with longer laser irradiation time. The size of AgNCs also increased with higher laser intensity. The average size of AgNCs, investigated by a scanning electron microscope (SEM) was in the range of 75 -200 nm. The number of reduced atoms in AgNCs as a function of laser intensity showed that the AgNCs are apparently produced by a four photon process, implying that the formation of dimer silver atoms is essential for the formation.

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Highly Efficient Photon Upconversion in Self-Assembled Light-Harvesting Molecular Systems

Cited by 160 publications

References 53 publications

Efficient Triplet Exciton Fusion in Molecularly Doped Polymer Light‐Emitting Diodes

Efficient Triplet Exciton Fusion in Molecularly Doped Polymer Light‐Emitting Diodes

Kinetically controlled crystal growth approach to enhance triplet energy migration-based photon upconversion

Formation and Growth of Silver Nanocubes upon Nanosecond Pulsed Laser Irradiation: Effects of Laser Intensity and Irradiation Time

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