Magnetic field effects on singlet fission dynamics

Singlet fission holds great potential to boost the efficiencies of solar cells by converting one photo-excited singlet exciton into two triplets via an intermediate state of triplet pairs with different exchange couplings. Magnetic field effects (MFEs) are induced by spin mixing between the triplet pair manifolds with different spin characteristics. The strongly and weakly coupled triplet pairs exhibit MFEs with magnetic field strength in different regimes. The quintet channel is the major pathway for highly efficient generation of free triplets. Singlet-quintet mixing is enabled by dynamic equilibrium between strongly and weakly couple triplet pairs through spatial separation and/or structure fluctuation. Intermediate intertriplet coupling is suggested for the efficient generation and dissociation of triplet pairs for highly efficient singlet fission for practical applications. Singlet fission can double the photon-to-electron conversion efficiency by splitting a singlet exciton into two triplets via an intermediate state of a triplet pair. The spin mixing of tripletpair manifolds with different spin characters is a determining factor for the efficiency of final triplet generation. In this review, we summarize recent studies of magnetic field effects (MFEs) on singlet fission dynamics, from theoretical models to recent experimental results. The analyses of MFEs support a three-step model with dynamic equilibrium between strongly and weakly coupled triplet pairs, suggesting an intermediate regime of intertriplet coupling to be favorable for singlet-quintet mixing toward efficient triplet generation for practical applications. Singlet fission can double the photon-to-electron conversion efficiency by splitting a singlet exciton into two triplets via an intermediate state of a triplet pair. The spin mixing of tripletpair manifolds with different spin characters is a determining factor for the efficiency of final triplet generation. In this review, we summarize recent studies of magnetic field effects (MFEs) on singlet fission dynamics, from theoretical models to recent experimental results. The analyses of MFEs support a three-step model with dynamic equilibrium between strongly and weakly coupled triplet pairs, suggesting an intermediate regime of intertriplet coupling to be favorable for singlet-quintet mixing toward efficient triplet generation for practical applications. triplets created by singlet fission fuse back to singlet states, which recombine to the ground state and emit fluorescence. Delayed fluorescence is induced by the regenerated singlets, which has a later arrival in the time domain than the fluorescence emission from direct optical excitation. transfer of excited electrons from one molecule to another via a nonradiative path, which requires a wavefunction overlap between the two molecules. states of a quantized system in which one of the variables (i.e., energy or angular momentum) defining the state has a fixed value (eigenvalue). operator corresponding to the total energy of a system. on symmetry grounds, certain ‘forbidden’ vibronic transitions are activated due to ‘intensity borrowing’ via a nontotally symmetric mode of appropriate symmetry, known as Herzberg–Teller mixing. energies of two levels are tuned by an external field to near-degeneracy. in a static magnetic field, the spin degeneracy is lifted with multi-sublevels separated due to Zeeman interactions. An external microwave field may mix the sublevels with resonance energy difference, leading to a change in fluorescence emission. By detecting the emission intensity as a function of magnetic field amplitude, we can observe the resonance phenomenon and calculate the magnitude of the interaction. time-domain oscillation behaviors of populations of excited states in a superposition, which may be probed by time-resolved spectroscopy. in a single junction organic solar cell, the detailed balanced limit of power conversion efficiency was predicted to be ~30% in a seminal paper by Shockley and Queisser [5.Shockley W. Queisser H.J. Detailed balance limit of efficiency of p-n junction solar cells.J. Appl. Phys. 1961; 32: 510Crossref Scopus (8866) Google Scholar]. temporal resolution technique used to directly detect changes in microwave intensity due to transitions between levels of different spin characters. in a magnetic field, the spin degenerate states are split into several components, first discovered by Pieter Zeeman. contains various types of interaction that split degenerate states even in the absence of a magnetic field.