Organic-inorganic lead halide perovskite solar cells (PSCs) offer a promising low-cost manufactural solar technology as they are compatible with large-scale and low-temperature (<100 °C) solution processes. Through the optimization of perovskite active layer and phenyl-C 61 -butyric acid methyl ester (PC 61 BM) layer thickness, the normal cells showed 9.7% power conversion efficiency (PCE). Compared with the corresponding normal devices, we observed an improvement in PCE from 9.7% to 11.3% and 10.2% for the devices prepared using 1 vol% of C 3 H 7 NH 3 I and 1 vol% of C 4 H 9 NH 3 I as additives, respectively. Via analysis by ultraviolet-visible (UV-vis) spectroscopy, grazing incidence wide angle X-ray diffraction (GIWAXS), and field emission scanning electron microscopy (FE-SEM), we concluded that the morphological changes, absorption, and crystallinity of the perovskite films played an important role that influenced the performance of the PSC devices with various additives. The presence of 1% of C 3 H 7 NH 3 I or 1% of C 4 H 9 NH 3 I caused the CH 3 NH 3 PbI 3-x Cl x films to grow uniformly with high coverage and continuous phase, as well as with higher absorption; this enabled the corresponding devices to display improved performance.