A large set of candidates for singlet fission, one of the most promising processes able to improve the efficiency of solar cells, are identified by screening a database of known molecular materials.
We use a large database of known molecular semiconductors to define a plausible physical limit to the charge carrier mobility achievable within this materials class, and a clear path toward this limit. From a detailed study of the desirable properties in a large dataset, it is possible to establish whether such properties can be optimized independently and what would be a reasonably achievable optimum for each of them, regardless of the transport mechanism considered. We compute all relevant parameters from a set of almost five thousand known molecular semiconductors, finding that the best known materials are not ideal with respect to all properties. These parameters in decreasing order of importance are realized to be the molecular area, the non-local electron-phonon coupling, the two-dimensional nature of transport, the local electron-phonon coupling and the highest transfer integral. We also find that the key properties related to the charge transport are either uncorrelated or 'constructively' correlated (i.e. they improve together) concluding that a ten-fold increase in mobility is within reach in a statistical sense, on the basis of the available data. We demonstrate that high throughput screenings, when coupled with physical models of transport produce not only specific target materials, as it is done also here, but a more general physical understanding of the materials space and the opportunities of further development.
We describe a practical and flexible
procedure to compute the charge
carrier mobility in the transient localization regime. The method
is straightforward to implement and computationally very inexpensive.
We highlight the practical steps and provide sample computer codes.
To demonstrate the flexibility of the method and generalize the theory,
the correlation between the fluctuations of the transfer integrals
is assessed. The method can be transparently linked with the results
of electronic structure calculations and can therefore be used to
extract the charge mobility at no additional cost.
Computing the charge mobility of molecular semiconductors requires a balanced set of approximations covering both the electronic structure of the Hamiltonian parameters and the modeling of the charge dynamics. For problems of such complexity, it is hard to make progress without independently validating each layer of approximation. In this perspective, we survey how all terms of the model Hamiltonian can be computed and validated by independent experiments and discuss whether some common approximations made to build the model Hamiltonian are valid. We then consider the range of quantum dynamics approaches used to model the charge carrier dynamics stressing the strong and weak points of each method on the basis of the available computational results. Finally, we discuss non-trivial aspects and novel opportunities related to the comparison of theoretical predictions with recent experimental data.
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