This Perspective reviews the developments of tin-based perovskite solar cells (PSCs) during the period 2014-2019 based on two organic cations (methylammonium vs formamidinium) and two device architectures (normal vs inverted) with the strategies of using cocations and coadditives. Unlike their lead-based analogues, tin-based PSCs suffer from the problems of Sn2+/Sn4+ oxidation and film formation. The current best cell is based on an inverted planar FASnI3 device with guanidinium as cocation, SnF2 as additive, and ethylenediammonium iodide as coadditive, which attains record efficiency near 10% with great stability. The device stability and performance might be further improved upon introducing bulky organic cations with a suitable coadditive to form a hybrid 2D/3D crystal structure. Considering the theoretical limit on device efficiency for tin-based PSCs to be ∼33%, there is much room for further performance improvement if the problems can be resolved according to the approaches discussed in this Perspective.