HC(NH2)2PbI3 perovskite solar cells have emerged as a promising alternative to CH3NH3PbI3 perovskite solar cells due to their better thermal stability and lower bandgap. In this work, we have demonstrated a reliable fabrication technique for HC(NH2)2PbI3 planar perovskite solar cells by controlling nucleation and crystallization processes of the perovskite layer through a combination of gas-assisted spin coating and the addition of HI additive in the perovskite precursor. A narrow distribution of power conversion efficiencies (PCEs) can be achieved with an average of 13% with negligible hysteresis when measured at a scanning rate of 0.1 V/s. The best performance device has a PCE of 16.0%. It is shown that by using optimized conditions we can consistently form dense, uniform, pinhole-free good crystalline, lead-iodide-impurities-free HC(NH2)2PbI3 film that has been comprehensively characterized by scanning electron microscopy, X-ray diffraction, Kelvin probe force microscopy, photoluminescence, and electroluminescence in this work.