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

TL;DR

This study uses terahertz transient photoconductivity measurements to analyze minority-carrier lifetimes in tin sulfide thin films, revealing key factors affecting their photovoltaic efficiency and providing a detailed methodology and software for such measurements.

Contribution

It introduces a detailed methodology and open-source software for measuring minority-carrier lifetimes in SnS thin films using THz photoconductivity, advancing metrology for early-stage photovoltaic materials.

Findings

Thermal annealing in H2S increases carrier lifetime.

Surface oxidation reduces surface recombination velocity.

Carrier lifetime remains below 100 ps across tested samples.

Abstract

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.