Nankai University’s Chen Yongsheng: AM—20.3%! How should the 2D conjugated core unit of high-performance acceptors be designed?

Article Introduction

Currently, nearly all high-performance acceptors are centered on electron-deficient diimide architectures, which severely constrains further innovation in acceptor molecular design.

Based on this, Yao Chaoyang and Chen Yongsheng of Nankai University, among others By employing oxygen (O), sulfur (S), and nitrogen (N) atoms as bridging units between 2D conjugated core centers, three receptor platforms—CH–O, CH–S, and CH–N—are generated, differing structurally by only two atoms. Owing to their distinctive outer-electron configurations and hybridization orientations, the O-, S-, and N-bridged core centers exhibit markedly distinct conformations and electronic properties: dibenzo-dioxin is planar and non-aromatic, thianthrene is folded and non-aromatic, and phenazine is planar and aromatic. A systematic study has, for the first time, elucidated how the core center—particularly the p–π orbital overlap between its lone pairs on the O/S/N atoms and the coplanar benzene moieties—affects the intrinsic optoelectronic properties of the receptor. Finally, the CH–N-based binary device achieved a record fill factor of 83.13% and a state-of-the-art power conversion efficiency of 20.23% in organic photovoltaics. By comprehensively evaluating rigorously controlled O-, S-, and N-bridged molecular platforms, this work reveals the potentially unique role of diimides in achieving excellent photovoltaic performance in acceptor materials. The paper was recently published in the journal under the title “O, S, and N Bridged Atoms Screening on 2D Conjugated Central Units of High‐Performance Acceptors.” Advanced Materials Up.

In summary, to expand the design space for SMAs, O, S, and N atoms are employed to bridge the 2D conjugated core on a single acceptor platform, giving rise to three distinct CH–O, CH–S, and CH–N SMAs. Due to the differing p-orbital–π* interactions among the lone pairs on O, S, and N and the adjacent phenyl planes, the central core of each SMA exhibits markedly different conformations and electronic properties: for instance, the planar, non-aromatic dibenzodioxin–O unit in CH–O, the buckled, non-aromatic thianthrene–S unit in CH–S, and the planar, aromatic phenazine–N unit in CH–N. A systematic study demonstrates that the intrinsic optoelectronic properties of SMAs can be finely tuned by modulating the characteristics of the central unit. Benefiting from the advantages of phenazine, the power conversion efficiency (PCE) of the D18:CH–N-based binary OSC reaches 20.23%, whereas that of D18:CH is 18.48% for the –O variant and 18.93% for the D18:CH–S variant. Notably, in addition to the pioneering Y-series backbones (such as L8-BO and BTP-eC9), the CH–N motif also exhibits a rare SMA scaffold, which can boost the PCE of binary OSCs to over 20%. Even more excitingly, D18:CH also achieves the highest fill factor of 83.13% among organic photovoltaics—N. By rationally tailoring the central unit in SMAs, this work demonstrates substantial potential for narrowing the fill-factor gap between organic and inorganic photovoltaics. Through the construction of these three SMAs, our study expands the structural diversity of the central unit and provides valuable guidance for future central-core design.

Device Fabrication

Device fabrication:

ITO/2PACz/D18:SMAs/PNDIT-F3N/Ag

1. Wash the ITO glass thoroughly, treat with ozone for 15 minutes, spin-coat with 2PACz at 3000 rpm for 20 seconds, and then anneal at 100°C for 10 minutes;

2. Completely dissolve the D18:CH-O, D18:CH-S, and D18:CH-N mixture (D:A weight ratio = 1:1.5; total concentration = 10.0 mg mL⁻¹) in chloroform (CF). Stir the mixed solution at 60°C for 3 hours, perform spin coating at 2200 rpm for 30 seconds, anneal at 85°C for 5 minutes, and then use CS. ₂ Perform SVA treatment using a solvent;

3. Spin-coat at 3,000 rpm for 20 seconds using a PNDIT-F3N solution in MeOH with 0.5% glacial acetic acid, at a concentration of 1 mg/mL;

4. Evaporate 150 nm of Ag.

X. Cao, Z. Xu, R. Wang, J. Guo, W. Zhao, Y. Zhang, Z. Yao, Y. Guo, G. Long, X. Wan, Y. Chen, O, S, and N Bridged Atoms Screening on 2D Conjugated Central Units of High‐Performance Acceptors. Advanced Materials, (2025).

DOI: 10.1002/adma.202503131