  Currently, Sb$_2$Se$_3$ thin films receive considerable research interest as
a solar cell absorber material. When completed into a device stack, the major
bottleneck for further device improvement is the open circuit voltage, which is
the focus of the work presented here. Polycrystalline thin film Sb$_2$Se$_3$
absorbers and solar cells are prepared in substrate configuration and the
dominant recombination path is studied using photoluminescence spectroscopy and
temperature dependent current-voltage characteristics. It is found that a
post-deposition annealing after the CdS buffer layer deposition can effectively
remove interface recombination since the activation energy of the dominant
recombination path becomes equal to the bandgap of the Sb$_2$Se$_3$ absorber.
The increased activation energy is accompanied by an increased
photoluminescence yield, i.e. reduced non-radiative recombination. Finished
Sb$_2$Se$_3$ solar cell devices reach open circuit voltages as high as 485 mV.
Contrarily, the short-circuit current density of these devices is limiting the
efficiency after the post-deposition annealing. It is shown that atomic layer
deposited intermediate buffer layers such as TiO$_2$ or Sb$_2$Se$_3$ can pave
the way for overcoming this limitation.
