•Discuss chemical structure design and correlate with device performance.•Progress includes the use of fused rings systems, 2D-3D approaches, and balancing solubility and aggregation.•Research with non-fullerene acceptors have led to efficiencies that surpass that of fullerene-based devices.Organic photovoltaic materials have the potential to revolutionize the solar energy industry as they are compatible with printing technologies that produce thin, flexible solar cells. In order for such material to be commercially viable, high power conversion efficiency (PCE) is necessary. The PCE of organic photovoltaic cells is largely determined by the material in the photoactive layer. Many different structures and types of organic materials for the active layer have been explored, such as benzodithiophene-based polymers and fused-ring ladder-type molecules. In recent years PCE values have neared or exceeded the theorized lower PCE limit of 10% for commercialization. In this review, the authors explore organic electron donors and acceptors that have been developed in the past 3 years (2013–2016) and have led to high-efficiency photovoltaic devices. Ultimately, the steadily climbing PCE values in recent years and variety of materials producing high PCEs points to a bright future for this area of solar energy.

•The performance of semiconducting polymers is currently limited by their low dielectric constant in the range of 3–4.•Increasing εr > GHz will enhance both charge separation and transport, leading to improved power conversion efficiency.•Electric field-induced tautomerization in fluorescein monopotassium salt copolymers can increase the electronic εr.The low dielectric constant (εr ∼ 3–4) for semiconducting polymers has been a major cause for their poor performance compared with the inorganic semiconductors, which possess high dielectric constants above 10. This study aimed to increase the electronic/atomic dielectric constant at high frequencies (i.e., εr∞) for semiconducting polymers. A new design strategy was proposed based on the electric field-induced tautomeric structures in conjugated fluorescein. To achieve this goal, fluorescein monopotassium salt-containing random copolymers were synthesized with 50 and 75 mol.% functionality. To reduce the strong electrostatic attraction between the K+ cation and the phenolate anion, 18-crown-6 ether was complexed with K+ in the fluorescein copolymers. A relatively high εr∞ of ∼5.5 and high electron mobility of 0.153 cm2/(V·s) were achieved for the 75 mol.% fluorescein K+/18C6 copolymer. The high electron mobility could be attributed to the relatively high static dielectric constant (εrs ∼ 9 at 1 Hz) of the sample. The fluorescein monopotassium salt copolymers behaved as n-type semiconductors with an optical band gap around 2.26 eV.