Low processing temperatures explored in Sb2S3 solar cells by close-spaced sublimation and analysis of bulk and interface related defects

Antimony trisulfide (Sb₂S₃) is a promising photovoltaic absorber, which has so far been fabricated mainly by chemical deposition methods. Despite its aptness for congruent sublimation, less research efforts have been made on low-temperature Sb₂S₃ processing by physical methods. In this regard, recent studies show large variation in the processing temperature of Sb₂S₃ films, which overall brings into question the need for higher substrate temperatures (>350 °C). Furthermore, in-depth analysis of defect structure of Sb₂S₃ employing temperature-dependent admittance spectroscopy (TAS) and photoluminescence (PL) remains largely unexplored. In this work, we systematically study the effect of close-spaced sublimation (CSS) substrate temperature on Sb₂S₃ absorber growth, employing a wide temperature range of 240–400 °C. Temperatures above 320 °C caused cracking phenomena in the Sb₂S₃ absorber film, proving the unviability of higher processing temperatures. CSS processing temperature of 300 °C was found optimal, producing crack-free Sb₂S₃ films with increased presence of (hk1) planes, and achieving the best CdS/Sb₂S₃ device with photoconversion efficiency of 3.8%. TAS study revealed two deep defects with activation energies of 0.32 eV and 0.37 eV. Low-temperature PL measurement revealed a band-to-band emission at 1.72 eV and a broad band peaked at 1.40 eV, which was assigned to a donor-acceptor pair recombination. Temperature-dependent I-V analysis showed that recombination at CdS–Sb₂S₃ interface remains a large limitation for the device efficiency.