Cu^sub 2^ZnSnS^sub 4^ thin film solar cells from coated nanocrystals ink

Earth abundant Cu^sub 2^ZnSnS^sub 4^ (CZTS) has triggered great attention in the field of low cost thin film solar cells. High-quality CZTS nanocrystals were synthesized by a facile solution method, with an average particle diameter about 12 nm and a direct band gap of 1.49 eV. And these nanocrystals were readily dispersed to form a colloidal ink, which was then used to prepare thin films by doctor blading approach. Effects of sulfurization temperature on those films' composition, morphology and phase were studied. The obtained thin film, annealed under flow S/Ar atmosphere at 550 °C for 30 min, shows a dense smooth surface, a slightly Cu-poor and Zn-rich composition and the kesterite CZTS structure. Besides, this 550 °C annealed CZTS film was then fabricated into full photovoltaic device and a power conversion efficiency of 2.29 % has been achieved. Directions for further improvements have also been discussed and proposed.