Many years back the measurement of diffusion coefficient and lifetime of dye-sensitized solar cells consistently showed that the parameters displayed a strong dependence with the voltage. Ideas explaining such behaviour date back to the seminal work of A. Rose in 1960s, but a consistent framework had not been formulated to account for the results of small perturbation techniques, that really allow a good definition of the parameters, since a kinetic constant can be uniquely associated to a position of the Fermi level. Many ideas were used in several works, such as the classical definition of the chemical diffusion coefficient, thermodynamic factor, and the quasistatic approximation that facilitates the integration of traps in the scheme. It emerged that a neat distinction can be made between single particle quantities like the jump diffusion coefficient and collective quantities like the chemical diffusion coefficient. But the lifetime took more time to clarify, since even the free carrier lifetime usually displays a dependence on Fermi level due to nonlinear recombination. Now in cooperation with Mehdi Ansari-Rad and Juan Antonio Anta a mor general framework has been developed that summarizes the previous theory and furthermore includes the lifetime in the scheme, consistently. I think this work provides a very complete theory for the interpretation of measurements of solar cells using disordered materials.
Diffusion and recombination in nanostructured materials25 06 2013
Mehdi Ansari-Rad, Juan A. Anta, and Juan Bisquert
J. Phys. Chem. C (Feature Article)