Triplet–triplet annihilation photon-upconversion: towards solar energy applications

Abstract

Solar power production and solar energy storage are important research areas for development of technologies that can facilitate a transition to a future society independent of fossil fuel based energy sources. Devices for direct conversion of solar photons suffer from poor efficiencies due to spectrum losses, which are caused by energy mismatch between the optical absorption of the devices and the broadband irradiation provided by the sun. In this context, photon-upconversion technologies are becoming increasingly interesting since they might offer an efficient way of converting low energy solar energy photons into higher energy photons, ideal for solar power production and solar energy storage. This perspective discusses recent progress in triplet-triplet annihilation (TTA) photon-upconversion systems and devices for solar energy applications. Furthermore, challenges with evaluation of the efficiency of TTA-photon-upconversion systems are discussed and a general approach for evaluation and comparison of existing systems is suggested.

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

“…The highest Φ TTA-UC and η TTA-UC for rubrene are 23% and 70%, respectively (For DPA and perylene, the efficiencies are slightly lower). 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).…”

“…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.…”

“…This reaction obeys spin conservation and is referred to as triplet fusion or TTA-UC in the upconversion literature. [9][10][11][12][13][14] In Stage III, the triplet-fusion-generated singlet recombines and produces delayed emission.…”

“…[6][7][8] At the same time, photon upconversion through TTA has been widely considered for next-generation photovoltaic applications. [9][10][11][12][13][14] Effective upconverters have been demonstrated using combinations of a triplet sensitizer such as platinum octaethylporphyrin (PtOEP) [3] and a triplet acceptor/annihilator such as 9,10-diphenylanthracene (DPA), [15] perylene, [16] or rubrene.[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 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.…”

Photon upconversion sensitized by a Ru(II)-pyrenyl chromophore

“…Consequently, tremendous advancements have been achieved in photochemical upconversion by using metal-containing triplet sensitizers with a variety of organic-based triplet acceptors/annihilators in both fluid solution [20,22,[29][30][31][32] and various host matrices [33][34][35][36][37][38][39][40][41][42][43]. The ultimate goal of this research is to maximize the efficiency of real-world solar powered devices by imparting sub-bandgap sensitization via integration of UC technology [8][9][10]44,45]. This change in cell design should reduce the drastic losses owing to spectral mismatch between various sensitizers and semiconductor bandgaps.…”