A new wide bandgap polymer donor, PNDT‐ST, based on naphtho[2,3‐b:6,7‐b′]dithiophene (NDT) and 1,3‐bis(thiophen‐2‐yl)‐5,7‐bis(2‐ ethylhexyl)benzo[1,2‐c:4,5‐c′]dithiophene‐4,8‐dione (BDD) is developed for efficient nonfullerene polymer solar cells. To better match the energy levels, a new near infrared small molecule of Y6‐T is also developed. The extended π‐conjugation and less twist of PNDT‐ST provides it with higher crystallinity and stronger aggregation than the PBDT‐ST counterpart. The higher lowest occupied molecular orbital level of Y6‐T than Y6 favors the better energy level match with these polymers, resulting in improved open circuit voltage (Voc) and power conversion efficiency (PCE). The high crystallinity and strong aggregation of PNDT‐ST also induces large phase separation with poorer morphology, leading to lower fill factor and reduced PCE than PBDT‐ST. To mediate the crystallinity and optimize the morphology, PNDT‐ST and PBDT‐ST are blended together with Y6‐T, forming the ternary blend devices. As expected, the two compatible polymers allow continual optimization of the morphology by varying the blend ratio. The optimized ternary blend devices deliver a champion PCE as high as 16.57% with a very small energy loss (Eloss) of 0.521 eV. Such small Eloss is the best record for polymer solar cells with PCEs over 16% to date.

Increasing the active layer thickness without sacrificing the power conversion efficiency (PCE) is one of the great challenges faced by organic solar cells (OSCs) for commercialization. Recently, PM6:Y6 as an OSC based on a non‐fullerene acceptor (NFA) has excited the community because of its PCE reaching as high as 15.9%; however, by increasing the thickness, the PCE drops due to the reduction of the fill factor (FF). This drop is attributed to change in mobility ratio with increasing thickness. Furthermore, this work demonstrates that by regulating the packing and the crystallinity of the donor and the acceptor, through volumetric content of chloronaphthalene (CN) as a solvent additive, one can improve the FF of a thick PM6:Y6 device (≈400 nm) from 58% to 68% (PCE enhances from 12.2% to 14.4%). The data indicate that the origin of this enhancement is the reduction of the structural and energetic disorders in the thick device with 1.5% CN compared with 0.5% CN. This correlates with improved electron and hole mobilities and a 50% suppressed bimolecular recombination, such that the non‐Langevin reduction factor is 180 times. This work reveals the role of disorder on the charge extraction and bimolecular recombination of NFA‐based OSCs.

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Two novel perylene diimide (PDI)-based derivatives, Alq 3 -PDI and Alq 3 -PDI2, are synthesized by flanking a 3D tri(8-hydroxyquinoline)aluminum(III) (Alq 3 ) core with PDI and a helical PDI dimer (PDI2) to construct high-performance small molecular nonfullerene acceptors (SMAs). The 3D Alq 3 core significantly suppresses the molecular aggregation of the resulting SMAs, leading to a well-mixed blend with a PTTEA donor polymer and weak phase separation. Compared with Alq 3 -PDI, the extended π-conjugation of Alq 3 -PDI2 results in higher-order molecular packing, which improves the absorption and phase separation behavior. Thus, the Alq 3 -PDI2 devices have higher J sc and FF values and better device performance, which are further enhanced by a small amount of 4,4′-bipyridine (Bipy) as an additive. The coordination between Bipy and the Alq 3 core promotes molecular packing and phase separation, which lower charge recombination and enhanced charge collection in the resulting devices. Therefore, a largely improved J sc of 15.74 mA cm −2 and very high FF of 71.27% are obtained in the Alq 3 -PDI2 devices, resulting in a power conversion efficiency of 9.54%, which is the best value reported for PDI-based polymer solar cells. The coordination can also serve as a "molecular lock," which prevents molecular motion and thus improves device stability.

Here, new polymers named PBTT-Cn (n = 3, 4, or 5) have been designed based on carboxylate-functionalized thieno[3,2-b]thiophene units. The electroluminescence external quantum efficiencies (EQEEL) of pristine PBTT-C4 and C5...