Bandgap Tunable Ternary Cd(x)Sb(2–y)S(3−δ) Nanocrystals for Solar Cell Applications

[Image: see text] We report the synthesis and photovoltaic performance of a new nonstoichiometric ternary metal sulfide alloyed semiconductor–Cd(x)Sb(2–y)S(3−δ) nanocrystals prepared by the two-stage sequential ionic layer adsorption reaction technique. The synthesized Cd(x)Sb(2–y)S(3−δ) nanocrystals retain the orthorhombic structure of the host Sb(2)S(3) with Cd substituting a fraction (x = 0–0.15) of the cationic element Sb. The Cd(x)Sb(2–y)S(3−δ) lattice expands relative to the host, Sb(2)S(3,) with its lattice constant a increasing linearly with Cd content x. Optical and external quantum efficiency (EQE) spectra revealed that the bandgap E(g) of Cd(x)Sb(2–y)S(3−δ) decreased from 1.99 to 1.69 eV (i.e., 625–737 nm) as x increased from 0 to 0.15. Liquid-junction Cd(x)Sb(2–y)S(3−δ) quantum dot-sensitized solar cells were fabricated using the polyiodide electrolyte. The best cell yielded a power conversion efficiency (PCE) of 3.72% with the photovoltaic parameters of J(sc) = 15.97 mA/cm(2), V(oc) = 0.50 V, and FF = 46.6% under 1 sun. The PCE further increased to 4.86%, a respectable value for a new solar material, under a reduced light intensity of 10% sun. The PCE (4.86%) and J(sc) (15.97 mA/cm(2)) are significantly larger than that (PCE = 1.8%, J(sc) = 8.55 mA/cm(2)) of the Sb(2)S(3) host. Electrochemical impedance spectroscopy showed that the ZnSe passivation coating increased the electron lifetime by three times. The EQE spectrum of Cd(x)Sb(2–y)S(3−δ) has a maximal EQE of 82% at λ = 350 nm and covers the spectral range of 300–750 nm, which is significantly broader than that (300–625 nm) of the Sb(2)S(3) host. The EQE-integrated current density yields a J(ph) of 11.76 mA/cm(2). The tunable bandgap and a respectable PCE near 5% suggest that Cd(x)Sb(2–y)S(3−δ) could be a potential candidate for a solar material.