Nonlinear optoelectronic processes in organic optoelectronic devices: Triplet-triplet annihilation and singlet fission

Sensitizer-free photon up conversion in (HQ)2ZnCl4 and HQCl crystals: systems involving resonant energy transfer and triplet–triplet annihilation

“…Recently, many pioneering works have been reported on new free sensitizer up-conversion systems that do not include heavy or precious metals. In such systems the triplet levels are not populated via ISC mechanism, but rather via spin orbit coupling as for the case of anthracene bromide 21 or via singlet-triplet fission mechanism like that has been described for many organic crystalline systems such as pentacene [22][23][24][25] tetracene 22,23 or solid tiophene based organic polymers. 24 Let's remind that Singlet -Fission mechanism (SF) is described as a bimolecular process occurring between two identical or different organic molecules with aromatic rings.…”

“…Among the possible free -sensitizer mechanisms, it seems that the singlet -fission process followed by triplet-triplet annihilation perfectly describes this up-conversion process from NIR to visible region. As we have already pointed out, many recent studies have been carried out on up-conversion systems involving singlet fission (SF) processes such as pentacene [22][23][24][25] tetracene 22,23 or solid tiophene based organic polymers. 24 In these studies it has been established that SF is conditioned mainly by the following criteria: (i) SF is a bimolecular process occurring between two chromophore molecules containing at least two aromatic rings and the energy of the singlet level is almost equal to twice the energy of the triplet level (ii) in the solid state, the  stacking of aromatic rings and their interaction favours and facilitates SF process (iii) the triplet exciton diffuses from a molecule to an other via Dexter transfer which consists of an electron exchange at short distances not exceeding 1 nm.…”

Application of Triplet–Triplet Annihilation Upconversion in Organic Optoelectronic Devices: Advances and Perspectives

“…[82,83] Though the maximum internal conversion efficiency is not as high as other materials (such as phosphorescent and TADF molecules), TTA has attracted much attention owing to its inherent merits, such as efficient blue emission, small efficiency roll-off, low operation voltage, and low cost. [84][85][86][87][88][89][90][91] Efficiency roll-off in electroluminescence devices means the device efficiency decreases as the brightness increases, which may be caused by singlet-triplet annihilation, singlet-polaron annihilation, and loss of charge carrier balance, etc. [92] Moreover, the unique structure of most TTA materials with relatively rigid conjugation enables their possibility for integrating high carrier mobility and efficient triplet utilization in one molecule, which are attractive for the fabrication of high performance single component OLETs.…”

High efficiency non-doped organic light emitting diodes based on pure organic room temperature phosphorescence by high-lying singlet exciton fission

“…2a). At same time, triplet-triplet annihilation (TTA) process that is the reverse process of SF should always be considered 34 . This process will also result in additional singlet excitons, thus the different ratios of singlet and triplet excitons.…”