Tunable Optical Properties in SnxSb2–yS3: A New Solar Absorber Material with an Efficiency of near 5%

Abstract

This work investigates the synthesis of a new ternary alloyed metal sulfide semiconductor SnxSb2–yS3 and its application in solar cells. SnxSb2–yS3 nanocrystals were synthesized by incorporating Sn2+ ions into the host binary Sb2S3 semiconductor using a two-step sequential ionic layer adsorption reaction (SILAR) process. The ternary SnxSb2–yS3 semiconductor maintains the monoclinic crystalline structure of the binary Sb2S3 host with a small expansion in lattice constants relative to that of Sb2S3. Energy-dispersive X-ray analysis revealed the nominal chemical composition of the sample with eight SILAR cycles to be Sn0.52Sb1.48S3. The energy gap Eg of SnxSb2–yS3 decreases with increasing Sn content x, resulting in a tunable Eg from 620 to 800 nm (i.e., 2.0–1.5 eV) for x = 0–0.56. Liquid-junction quantum dot-sensitized solar cells were fabricated, for the first time, from the prepared SnxSb2–yS3 nanocrystals using the polyiodide electrolyte. The best cell yielded an efficiency of 2.58% with the photovoltaic parameters of Jsc = 14.04 mA/cm2, Voc = 0.46 V, and FF = 39.9% under 1 sun. The efficiency improved to a respectable value of 4.89% under the reduced light intensity of 0.05%. The external quantum efficiency (EQE) spectrum has a maximal EQE of 71.8% at λ = 500 nm and covers the spectral range of 300–800 nm, which is significantly broader than that (300–620 nm) of the host Sb2S3. The broader optical absorption band increases light harvesting and results in a Jsc ≈ 64% larger than that of the host Sb2S3. The result demonstrates the tunable optical properties of SnxSb2–yS3 by controlling the cationic Sn and Sb compositions, which is a favorable property for a solar absorber.