Side‐chain tailoring is a promising method to optimize the performance of organic solar cells (OSCs). However, asymmetric alkyl chain‐based small molecular acceptors (SMAs) are still difficult to afford. Herein, we adopted a novel asymmetric n‐nonyl/undecyl substitution strategy and synthesized two A‐D1A′D2‐A double asymmetric isomeric SMAs with asymmetric selenophene‐based central core for OSCs. Crystallographic analysis indicates that AYT9Se11‐Cl forms a more compact and order intermolecular packing compared to AYT11Se9‐Cl, which contributed to higher electron mobility in neat AYT9Se11‐Cl film. Moreover, the PM6 : AYT9Se11‐Cl blend film shows a better morphology with appropriate phase separation and distinct face‐on orientation than PM6 : AYT11Se9‐Cl. The OSCs with PM6 : AYT9Se11‐Cl obtain a superior PCE of 18.12 % compared to PM6 : AYT11Se9‐Cl (17.52 %), which is the best efficiency for the selenium‐incorporated SMAs in binary BHJ OSCs. Our findings elucidate that the promising double asymmetric strategy with isomeric alkyl chains precisely modulates the crystal packing and enhances the photovoltaic efficiency of selenophene‐incorporated SMAs.

Although all‐polymer solar cells (all‐PSCs) show great commercialization prospects, their power conversion efficiencies (PCEs) still fall behind their small molecule acceptor‐based counterparts. In all‐polymer blends, the optimized morphology and high molecular ordering are difficult to achieve since there is troublesome competition between the crystallinity of the polymer donor and acceptor during the film‐formation process. Therefore, it is challenging to improve the performance of all‐PSCs. Herein, a ternary strategy is adopted to modulate the morphology and the molecular crystallinity of an all‐polymer blend, in which PM6:PY‐82 is selected as the host blend and PY‐DT is employed as a guest component. Benefiting from the favorable miscibility of the two acceptors and the higher regularity of PY‐DT, the ternary matrix features a well‐defined fibrillar morphology and improved molecular ordering. Consequently, the champion PM6:PY‐82:PY‐DT device produces a record‐high PCE of 18.03%, with simultaneously improved open‐circuit voltage, short‐circuit current and fill factor in comparison with the binary devices. High‐performance large‐area (1 cm2) and thick‐film (300 nm) all‐PSCs are also successfully fabricated with PCEs of 16.35% and 15.70%, respectively.Moreover, 16.5 cm2 organic solar module affords an encouraging PCE of 13.84% when using the non‐halogenated solvent , showing the great potential of “Lab‐to‐Fab” transition of all‐PSCs.

Selenium-heterocyclic and side-chain strategies for developing near-infrared (NIR) small fused-ring acceptors (FRAs) to further obtain short-circuit current density (J sc ) have proven advantageous in the top-performing polymer solar cells (PSCs). Herein, a new electron-rich central selenium-containing heterocycle core (BTSe) attaching alkyl side chains with a terminal phenyl group was coupled with a difluorinated and dichlorinated electron-accepting terminal 1,1-dicyanomethylene-3-indanone (IC) to afford two types of new FRAs, BTSe-IC2F and BTSe-IC2Cl. Interestingly, in spite of the weaker intramolecular charge transfer, BTSe-IC2F shows a stronger NIR response because of the smaller bandgap (E g opt ) up to 1.26 eV, benefiting from the stronger ordered molecular packing in comparison to BTSe-IC2Cl with an E g opt of 1.30 eV. Additionally, thermal annealing induced an evident red shift by ∼50 nm in the absorption of D18:BTSe-IC2F blend films. Such a phenomenon may be attributed to the synergistic impact of the formation of inward constriction toward the molecular backbone because of the combination of bulky side chains and fluorinated IC as well as the reduced aromaticity of the selenium heterocycle. Consequently, the thermally annealed device based on BTSe-IC2F/D18 achieves a champion power conversion efficiency (PCE) of 17.3% with a high fill factor (FF) of 77.22%, which is among the highest reported PCE values for selenium-heterocyclic FRAs in binary PSCs. The improved J sc and FF values of the D18:BTSe-IC2F film are simultaneously achieved mainly because of the preferred face-on orientations, the wellbalanced electron/hole mobility, and the favorable blend morphology compared to D18:BTSe-IC2Cl. This work suggests that the selenium-heterocyclic fused-ring core (with proper side chains) combined with fluorinated terminal groups is an effective strategy for obtaining highly efficient NIR-responsive FRAs.

Recently, sequential layer‐by‐layer (LbL) organic solar cells (OSCs) have attracted significant attention owing to their favorable p–i–n vertical phase separation, efficient charge transport/extraction, and potential for lab‐to‐fab large‐scale production, achieving high power conversion efficiencies (PCEs) of over 18%. This review first summarizes recent studies on various approaches to obtain ideal vertical D/A phase separation in nonfullerene acceptor (NFAs)‐based LbL OSCs by proper solvent selection, processing additives, protecting solvent treatment, ternary blends, etc. Additionally, the longer exciton diffusion length of NFAs compared with fullerene derivatives, which provides a new scope for further improvement in the performance of LbL OSCs, is been discussed. Large‐area device/module production by LbL techniques and device stability issues, including thermal and mechanical stability, are also reviewed. Finally, the current challenges and prospects for further progress toward their eventual commercialization are discussed.

Herein, we synthesized new hetero‐halogenated end groups with well‐determined fluorinated and chlorinated substitutions (o‐FCl‐IC and FClF‐IC), and synthesized regioisomer‐free small molecular acceptors (SMAs) Y‐Cl, Y‐FCl, and Y‐FClF with distinct hetero‐halogenated terminals, respectively. The single‐crystal structures and theoretical calculations indicate that Y‐FClF exhibits more compact three‐dimensional network packing and more significant π‐π electronic coupling compared to Y‐FCl. From Y‐Cl to Y‐FCl to Y‐FClF, the neat films exhibit a narrower optical band gap and gradually enhanced electron mobility and crystallinity. The PM6 : Y‐FClF blend film exhibits the strongest crystallinity with preferential face‐on molecular packing, desirable fibrous morphology with suitable phase segregation, and the highest and balanced charge mobilities among three blend films. Overall, the PM6 : Y‐FClF organic solar cells (OSCs) deliver a remarkable efficiency of 17.65 %, outperforming the PM6 : Y‐FCl and PM6 : Y‐Cl, which is the best PCE for reported hetero‐halogens‐based SMAs in binary OSCs. Our results demonstrate that difluoro‐monochloro hetero‐terminal is a superior regio‐regular unit for enhancing the intermolecular crystal packing and photovoltaic performance of hetero‐halogenated SMAs.