Structure–property relationships of side-chain modified anthracene-containing poly(p-phenylene-ethynylene)-alt-poly(p-phenylene-vinylene)s (PPE-PPV) copolymers were investigated in pristine constituents and bulk-heterojunction organic solar cells. The deliberate arrangement of linear octyloxy and branched 2-ethylhexyloxy side-chains within the segments of the PPE-PPV backbones resulted in a wide variety of side-chain-defined copolymers, denoted AnE-PVs. A number of pristine copolymers and their blends with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) were investigated by several characterization techniques and analyzed in detail. Compiling the experimental data enabled us to correlate the optoelectronic properties of the solar cells with the chemical structures of the copolymers, providing structural design rules for optimizing solar cell performance. Polymer structures—categorical variables with side-chains—are numerically represented before being used in statistical models. A linear regression framework was implemented to reveal systematic trends between the effective energy gap and the photovoltaic parameters. Among the photovoltaic parameters, the short-circuit current was identified as the most influential factor determining the overall power conversion efficiency.