  Thin films are gaining ground in photonics and optoelectronics, promising
improvements in their efficiency and functionality as well as decreased
material usage as compared to bulk technologies. However, proliferation of thin
films would benefit not only from continuous improvements in their fabrication,
but also from a unified and accurate theoretical framework of the interplay of
photons and charge carriers. In particular, such a framework would need to
account quantitatively and self-consistently for photon recycling and
interference effects. To this end, here we combine the drift-diffusion
formalism of charge carrier dynamics and the fluctuational electrodynamics of
photon transport self-consistently using the recently introduced
interference-extended radiative transfer equations. The resulting equation
system can be solved numerically using standard simulation tools, and as an
example, here we apply it to study well-known GaAs thin-film solar cells. In
addition to obtaining the expected device characteristics, we analyze the
underlying complex photon transport and recombination-generation processes that
represent a full solution to the inhomogeneous Maxwell's equations and that are
generated directly as a result of solving the self-consistent model. The
methodology proposed in this work is general and can be used to obtain accurate
physical insight into a wide range of planar optoelectronic devices, of which
the thin-film single-junction solar cells studied here are only one example.
