Two-stage synthesis of Bournonite (CuPbSbS3) thin films for photovoltaic applications

Abstract

Bournonite (CuPbSbS₃) exhibits promising characteristics as a photovoltaic light harvester. However, the solution-based methods commonly employed for its synthesis and device fabrication have prompted the exploration of physical vapor deposition (PVD) techniques. In this study, CuPbSbS₃ thin films and corresponding solar cells were synthesized using a two-stage approach: thermal evaporation of Sb/Cu/Pb/Cu metal precursors followed by sulfurization. The effect of sulfurization duration (5–30 min) on the growth and physical properties of the Bournonite thin films was systematically investigated. Films sulfurized for a short duration of 5 min exhibited minor PbS and CuSbS₂ secondary phases, crystallite sizes of approximately 68.1 nm, and grain sizes ranging from 0.5 to $1.0\mu m$. Increasing the sulfurization duration to 10–30 min eliminated the PbS secondary phase, improved stoichiometry and crystallinity (up to 71 nm), and resulted in larger grains (1.0–$1.5\mu m$). The films demonstrated high optical absorption coefficients exceeding 10⁴ cm⁻¹ in the visible region and a direct bandgap of 1.37–1.41 eV. Thin-film solar cells fabricated using these absorber layers showed a decrease in performance with longer sulfurization times, attributed to reduced carrier mobility. As the sulfurization duration increased from 5 to 30 min, the device efficiency dropped from 0.13% to 0.08%, short-circuit current density (J${}_{sc}$) from 1.59 to 1.28 mA/cm², open-circuit voltage (V${}_{oc}$) from 269.1 to 220.9 mV, and fill factor (FF) from 29.6% to 26.6%. These promising initial results establish a foundation for the development of high-efficiency Bournonite thin-film solar cells using PVD techniques.