Two-dimensional (2D) Ruddlesden-Popper perovskites have shown great potential for application in perovskite solar cells due to their appealing environmental stability. However, 2D perovskites generally show poor photovoltaic performance. Here, a new type of 2D perovskite using 2-thiophenemethylammonium (ThMA(+)) as a spacer cation was developed and high photovoltaic performance as well as enhanced stability in comparison with its 3D counterpart was demonstrated. The use of the 2D perovskite (ThMA)(2)(MA)(n-1)PbnI3n+1,1 (n = 3) in deposited highly oriented thin films from N,N-dimethylformamide using a methylammonium chloride (MACI) assisted film-forming technique dramatically improves the efficiency of 2D perovskite photovoltaic devices from 1.74% to over 15%, which is the highest efficiency for 2D perovskite (n < 6) solar cells so far. The enhanced performance of the 2D perovskite devices using MACl as additive is ascribed to the growth of a dense web of nanorod-like film with near-single-crystalline quality, in which the crystallographic planes of the 2D MA(n-1)Pb(n)I(3n+1)(2-) slabs preferentially aligned perpendicular to the substrate, thus facilitating efficient charge transport. This work provides a new insight into exploration of the formation mechanism of 2D perovskites with increased crystallinity and crystal orientation suitable for high-performance solar cells.