Cu₂ZnSnS₄ solar cells with a single spin-coated absorber layer prepared via a simple sol-gel route

Carbon-free Cu₂ZnSnS₄ (CZTS) thin films were prepared via a simple spin-coating process based on a sol-gel precursor of methoxyethanol solution with metal salts and thiourea, followed by post-sulfurization. The sol-gel precursor solution was deposited onto molybdenum-coated glass substrates. The sulfurization process was carried out using a conventional furnace at 525°C for 60min in a nitrogen atmosphere with sulfur powder. The structural, morphological and compositional properties of as-sulfurized thin films were characterized using X-ray diffraction, Raman spectroscopy, scanning electron microscopy and Auger electron spectroscopy. Only a single coating of the precursor solution was applied to obtain uniform Zn-rich and Cu-poor CZTS films thicker than 1μm after post-annealing. The best solar cell fabricated with the as-prepared CZTS films of band gap energy ~1.37eV showed a short-circuit current density of 10.15mA/cm², an open circuit voltage of 0.509V, a fill factor of 33.72% and a conversion efficiency of 1.74%.