Min Hun Jee

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.

Abstract 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‐D 1 A′D 2 ‐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.

High-performance organic solar cells often rely on halogen-containing solvents, which restrict the photovoltaic industry. Therefore, it is imperative to develop efficient organic photovoltaic materials compatible with halogen-free solvents. Herein, a series of benzo[a]phenazine (BP)-core-based small-molecule acceptors (SMAs) achieved through an isomerization chlorination strategy is presented, comprising unchlorinated NA1, 10-chlorine substituted NA2, 8-chlorine substituted NA3, and 7-chlorine substituted NA4. Theoretical simulations highlight NA3's superior orbit overlap length and tight molecular packing, attributed to interactions between the end group and BP unit. Furthermore, NA3 demonstrates dense 3D network structures and a record electronic coupling of 104.5 meV. These characteristics empower the ortho-xylene (o-XY) processed PM6:NA3 device with superior power conversion efficiency (PCE) of 18.94%, surpassing PM6:NA1 (15.34%), PM6:NA2 (7.18%), and PM6:NA4 (16.02%). Notably, the significantly lower PCE in the PM6:NA2 device is attributed to excessive self-aggregation characteristics of NA2 in o-XY. Importantly, the incorporation of D18-Cl into the PM6:NA3 binary blend enhances crystallographic ordering and increases the exciton diffusion length of the donor phase, resulting in a ternary device efficiency of 19.75% (certified as 19.39%). These findings underscore the significance of incorporating new electron-deficient units in the design of efficient SMAs tailored for environmentally benign solvent processing of OSCs.

Abstract 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 cm 2 ) and thick‐film (300 nm) all‐PSCs are also successfully fabricated with PCEs of 16.35% and 15.70%, respectively.Moreover, 16.5 cm 2 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.