Controlling Molecular Packing and Orientation via Constructing a Ladder-Type Electron Acceptor with Asymmetric Substituents for Thick-Film Nonfullerene Solar Cells

Abstract

A nonfullerene acceptor, IDTT-OB, employing indacenodithieno [3,2-b]thiophene (IDTT) decorated with asymmetric substituents as the core, is designedly prepared. In comparison with the analogue IDT-OB, extending the five-heterocyclic indacenodithiophene (IDT) core to seven-heterocyclic fused ring endows IDTT-OB with more broad absorption and elevated highest occupied molecular orbital energy level. In addition, IDTT-OB shows a more intense molecular packing and a higher crystalline behavior with a strong faceon orientation in the neat film and the PBDB-T:IDTT-OB blend film. Furthermore, an ideal nanomorphology with a domain size of 19 nm can be obtained, which is in favor of exciton diffusion and charge separation. Accordingly, PBDB-T:IDTT-OB-based polymer solar cells demonstrate a maximum power conversion efficiency (PCE max ) of 11.19% with an impressive fill factor of 0.74, comparable to the stateof-the-art acceptors with similar molecular backbones. More importantly, IDTT-OB-based devices show good tolerance to the film thickness, which maintain a high PCE of 10.20% with a 250 nm thick active layer, demonstrating that the asymmetric acceptor is profound for fabricating high-efficiency thick-film nonfullerene solar cells.

Asymmetric Nonfullerene Small Molecule Acceptors for Organic Solar Cells

“…Most excitingly, this asymmetric IDT‐OB‐based OSCs could still maintain a high PCE of 9.17% when the thickness was increased to 210 nm, which represented the highest PCE value for the as‐cast thick‐film nonfullerene OSCs at that time. By changing the IDT in IDT‐OB to the more extended IDTT core, the same group reported another asymmetric A–D–A‐type nonfullerene SMA IDTT‐OB. In comparison with the asymmetric IDT‐OB, this asymmetric IDTT‐OB showed increased light‐harvesting ability, enhanced crystallinity, and better phased separation morphology when blended with PBDB‐T.…”

15.3% efficiency all-small-molecule organic solar cells enabled by symmetric phenyl substitution

“…On the basis of this strategy, several small molecular donors, such as benzodithiophene-Cl (BTR-Cl), BSFTR and BTEC-2F have been developed (see Table 1) and the corresponding OSCs achieve PCEs over 13% when blended with the small molecule acceptor Y6 [28][29][30]. It is well known that variations in morphology induced by the changes in crystallinity and molecular orientation have a significant impact on the performance of OSCs [31][32][33][34]. It is worth pointing out that the crystallization characteristics of the donor materials in these studies have all been regulated, and we infer that the improved crystallinity of donor compound may lead to stronger interactions between the donor and the NF acceptor materials to realize synergistic optimization of the morphology and benefit the high-performance NFSM-OSCs.…”

Over 15% Efficiency Polymer Solar Cells Enabled by Conformation Tuning of Newly Designed Asymmetric Small‐Molecule Acceptors

“…[ 13,21–27 ] Recently, the design of asymmetric molecules has captivated more and more attention due to its strong intermolecular binding energy and larger dipole moment, which are beneficial to reinforce intermolecular interaction, resulting in the increased fill factor (FF) and PCE in PSCs. [ 28–33 ] Extending core conjugation has been adopted to develop asymmetric SMAs, and functionalization on only side of symmetric core has been proved an effective method. Very recently, Yang and co‐workers synthesized two asymmetric molecules, namely, N7IT and N8IT, by incorporating a dithieno[3,2‐ b :2′,3′‐ d ]pyrrol (DTP) unit into one side of indaceno[3,2‐ b ]dithiophene (IDT) and indacenodithieno[3,2‐ b ]thiophene (IDTT) core, respectively.…”