  Materials research with a focus on enhancing the minority-carrier lifetime of
the light-absorbing semiconductor is key to advancing solar energy technology
for both early-stage and mature material platforms alike. Tin sulfide (SnS) is
an absorber material with several clear advantages for manufacturing and
deployment, but the record power conversion efficiency remains below 5%. We
report measurements of bulk and interface minority-carrier recombination rates
in SnS thin films using optical-pump, terahertz (THz)-probe transient
photoconductivity (TPC) measurements. Post-growth thermal annealing in H_2S gas
increases the minority-carrier lifetime, and oxidation of the surface reduces
the surface recombination velocity. However, the minority-carrier lifetime
remains below 100 ps for all tested combinations of growth technique and
post-growth processing. Significant improvement in SnS solar cell performance
will hinge on finding and mitigating as-yet-unknown recombination-active
defects. We describe in detail our methodology for TPC experiments, and we
share our data analysis routines as freely-available software.
