The low photovoltaic efficiency of iron pyrite-based solar cells is often related to the presence of sulfur deficiencies. In this paper surfur-rich iron pyrite nanocrystals (FeS₂ NCs) are synthesized by the hot injection method and deposited using layer by layer deposition. Optical absorption measurements show substantial sub-bandgap absorption, which is attributed to a sulfur-rich, thin surface layer. Microwave photoconductance measurements show very little signal of films with the original long ligands, while an approximately 100-fold higher signal is observed for films treated with FeCl₂ and 1,2-ethanedithiol (EDT) solutions. In mesoporous hybrid systems of FeS₂/SnO₂ both sub-band-gap and above-band-gap photons lead to electron injection from FeS₂ into the SnO₂ conduction band. We explain these findings by proposing that pinning of the Fermi level by the surface layer leads to a downward band bending in the direction of the surface within the FeS₂ NC. Hence, photoexcited electrons will first move toward the shell where they relax into empty surface states. As the holes remain behind in the core of the nanocrystals, this results in a charge-separated state with a long lifetime. Interestingly, these surface electrons are able to migrate in the FeS₂ NP layer by interparticle tunneling and can still decay by injection into SnO₂. Hence, our results indicate that SnO₂ is a suitable electron acceptor for FeS₂. The long-lived charge-separated electrons and holes could be exploited efficiently in photodetectors.