Towards all inorganic antimony sulphide semitransparent solar cells.

NiO, a wide band gap hole-transporting material (HTM), is gaining attention in photovoltaics due to its optical transparency, chemical stability, and favourable band alignment with absorber. This study uses NiO nanoparticle-based HTM in semi-transparent SbS solar cells via a simple chemical precipitation method. We optimised NiO layer by varying precursor solution concentration and studied its impact on optical and structural properties, composition of nanoparticles and subsequent effect on the performance of semi-transparent SbS solar cell. NiO nanoparticles, deposited from nickel(II)nitrate hexahydrate (precursor solution concentrations of 0.2 M to 1.2 M), were thermally treated by two steps at 90 °C for 6 h and 270 °C for 3 h. Nanoparticles with crystallite sizes of 6-9 nm had band gaps (Eg) of ca. 3.65-3.70 eV. Using 1.2 M concentration yielded the largest crystallites (9 nm), lowest Eg (3.65 eV) while retaining the most precursor residues. The highest power conversion efficiency (2.68%) was achieved with NiO from a 0.5 M precursor, a 60% improvement over HTM-free cells. The effect of precursor solution concentration on the solar cell parameters (efficiency, fill factor, open circuit voltage and short circuit current) are discussed. Present work paves a path toward stable, efficient, and cost-effective all-inorganic SbS solar cells using NiO HTM instead of organic counterparts.