Abstract
Iron pyrite (FeS2) is a promising photovoltaic absorber due to its earth abundance, non-toxic composition element, infrared band gap (Eg = 0.95 eV), and excellent photoabsorption characteristic (α>105 cm−1), which make it possible to allow the use of very thin (less than 100 nm) absorption layers. However, its use has been hindered because phase-pure pyrite nanocrystals are difficult to be synthesized. In this work, by the means of chemical method, we synthesized cube-like Pyrite nanoparticles (NPs) and Co-doped Pyrite NPs with high quality and both of their size are around 50 to 100 nm. Since the NPs are big and tend to agglomerate to a size over 100 nm, they are unable to form smooth, continuous ultrathin films with thickness less than 50nm. To solve this problem, bead mill at high milling speed was applied to smash the NPs into smaller pieces and then dispersed the agglomerate to yield well-dispersed pyrite NPs inks. After revising experimental parameters such as rotation speeds of rotor blade and weight ratio (WR) of Pyrite and surfactant(Oleylamine), we obtained the optimal experimental parameters to fabricate films with thickness about 30 nm by spin coating. The parameters are 1 wt. % pyrite slurry, rotor blade rotation speed at 2500 rpm, WR (Pyrite/OLA) of 5 and milling for 40 mins. Eventually, we annealed the as-deposited Pyrite thin films under sulfur atmosphere in order to remove the surfactant and defects. Moreover, we investigated the microstructures and optoelectronic properties of these films, finding that Pyrite thin films transfer from P-type to N-type after doping a small amount of Cobalt. Also, the analytical result shows that both of their carrier concentration are above 1017 cm-3 and their photoabsorption coefficient are above 2×〖10〗^5 cm-1 for wavelength below 700 nm.