Conventional inorganic solar cells can achieve high efficiencies, but are complicated and costly to produce. The desirability of a lower cost is driving the development of several third-generation solar cell technologies. Of these, the polymer solar cell (PSC) is particularly cheap to produce, as polymer solar panels can be fabricated using extremely high throughput roll-to-roll printing methods similar to those used to print newspapers. State-of-the-art PSCs consist of a blend film of a polymer and a fullerene derivative, which function as an electron-donor and an electron-acceptor, respectively. Although this type of polymer:fullerene solar cell achieves an impressive efficiency (9.2% for single-junction cells), the fullerene acceptors have several disadvantages. In the hope of addressing these issues, PSCs based on non-fullerene acceptors have been developed. In general, there are two alternatives for the replacement of fullerenes in PSCs. One choice is a polymer acceptor and the other is a small molecular acceptor. This chapter will have two main parts covering the material and morphological aspects of all-PSCs.