The photobioelectrochemical properties of a systematic series of conjugated oligoelectrolytes (COEs) were elucidated by direct modification of high-performance thylakoid bioanodes. In both three-electrode electrochemical cells and bio-solar cell devices, significant anodic performance enhancements (p < 0.1) were induced by addition of certain COEs. Amperometric photocurrent densities increased by up to 2.3-fold for the best COE. In bio-solar cell devices, short-circuit photocurrent increased by up to 1.7-fold and short-circuit dark current increased by up to 1.4-fold, indicating that the best COEs enhance both light harvesting and interfacial electron transfer. Trends in these results indicate that molecular energetics, molecular length, and the pendant charge of COEs all differentially contribute to photobioelectrochemical enhancements, and the optimal combination of these features is revealed. Optical absorbance characterization suggests that COE molecules reside in the thylakoid lipid bilayer, and photoluminescence studies implicate a FRET-type mechanism for the light harvesting enhancements. Control experiments indicate that COEs augment native thylakoid functionality, as COEs do not have redox activity or undergo chemical degradation.