Transient terahertz photoconductivity measurements of minority- carrier lifetime in tin sulfide thin films: Advanced metrology for an early stage photovoltaic material

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 H2S gas increases the minority-carrier lifetime, and oxidation of the surface reduces the surface recombination velocity. However, the minoritycarrier lifetime remains below 100 ps for all tested combinations of growth technique and postgrowth 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 in the form freelyavailable software.