We report a series of semi-crystalline, low band gap (LBG) polymers and demonstrate the fabrication of highly efficient polymer solar cells (PSCs) in a thick single-cell architecture. The devices achieve a power conversion efficiency (PCE) of over 7% without any post-treatment (annealing, solvent additive, etc.) and outstanding long-term thermal stability for 200 h at 130 °C. These excellent characteristics are closely related to the molecular structures where intra- and/or intermolecular noncovalent hydrogen bonds and dipole–dipole interactions assure strong interchain interactions without losing solution processability. The semi-crystalline polymers form a well-distributed nano-fibrillar networked morphology with PC70BM with balanced hole and electron mobilities (a h/e mobility ratio of 1–2) and tight interchain packing (a π–π stacking distance of 3.57–3.59 Å) in the blend films. Furthermore, the device optimization with a processing additive and methanol treatment improves efficiencies up to 9.39% in a ∼300 nm thick conventional single-cell device structure. The thick active layer in the PPDT2FBT:PC70BM device attenuates incident light almost completely without damage in the fill factor (0.71–0.73), showing a high short-circuit current density of 15.7–16.3 mA cm−2. Notably, PPDT2FBT showed negligible changes in the carrier mobility even at ∼1 μm film thickness.

The International Telecommunication Union announced a new color gamut standard of broadcast service television (BT 2020) for ultra-high-definition TV in 2012. To satisfy the wide-color gamut standard of BT 2020, monochromatic red (R), green (G), and blue (B) emissions require a small full width at half-maximum, which is an important property for improving color purity. Although organic light-emitting diode (OLED) displays are currently one of the main types of display technologies, their broad emission via strong vibronic coupling between ground and excited states is a major hurdle to overcome in the development of next-generation wide-color gamut displays. Thus, the development of OLED emitters with narrowband R–G–B emissions is of great significance. In this review, the recent progress in the development of OLED materials with narrowband emission is summarized by grouping them into fluorescent, phosphorescent, and thermally activated delayed fluorescent emitters to reveal the correlation between molecular structures, optical properties, and device characteristics. We discuss rational molecular design strategies to achieve narrow photoluminescence and electroluminescence and the underlying mechanisms for controlling the emission bandwidth. Finally, the challenges in the realization of wide-color gamut OLED displays and the future prospects of such devices are discussed.

A new acceptor–donor–acceptor‐structured nonfullerene acceptor ITCC (3,9‐bis(4‐(1,1‐dicyanomethylene)‐3‐methylene‐2‐oxo‐cyclopenta[b]thiophen)‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d′:2,3‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]‐dithiophene) is designed and synthesized via simple end‐group modification. ITCC shows improved electron‐transport properties and a high‐lying lowest unoccupied molecular orbital level. A power conversion efficiency of 11.4% with an impressive V _OC of over 1 V is recorded in photovoltaic devices, suggesting that ITCC has great potential for applications in tandem organic solar cells.