Recently, a joint team formed by Professor Tiankai Zhang from the School of Materials Science and Engineering at Southeast University, together with Professors Yaowen Li and Professor Xiankai Chen from Soochow University, proposed a novel interfacial self-assembly monolayer (SAM) design strategy for perovskite solar cells—"electronic resonance" SAM structure. The related results were published in the international top-tier journal Nature. This study provides a new solution to the problem of poor stability of perovskite solar cells under harsh conditions caused by the inherently weak anchoring strength of conventional interfacial SAMs.
Perovskite solar cells are lightweight, thin, and flexible, offering the potential to significantly expand the application scenarios of traditional photovoltaics. With the rapid development of their efficiency, the prospects for their industrialization are very promising. However, the main factor currently hindering the industrialization of perovskite solar cells is their relatively poor operational stability, especially the unsatisfactory operational lifespan under harsh conditions. One of the most vulnerable components in the device is the desorption of SAMs responsible for charge extraction. This layer is only a single molecule thick; once SAM molecules desorb, it leads to increased interfacial defects and a significant decline in device efficiency.
Currently, strategies employed by researchers to enhance the stability of SAMs include increasing the number of anchoring sites and introducing steric hindrance to inhibit molecular aggregation. However, insightful investigations and designs targeting to increase the intrinsic anchoring strength of the SAM on the substrate have yet to be carried out. This work focuses on enhancing the intrinsic bonding strength of the anchoring covalent bonds, fundamentally improving the anchoring stability of the SAM. Moreover, this approach can be combined with other existing strategies to further achieve breakthroughs in stability.
The underlying physical mechanism for the enhanced intrinsic strength of the anchoring covalent bond lies in the increased electron cloud density at the anchoring group. By designing an "electronic resonance" structure with an electron donor–acceptor–donor configuration, the electron cloud density at the acceptor moiety—namely, the anchoring group—can be effectively enhanced, leading to a shorter anchoring covalent bond length and higher anchoring covalent bond strength. Meanwhile, this "electronic resonance" monolayer also enables better interfacial coverage uniformity, achieving simultaneous improvements in both the stability and efficiency of perovskite solar cell devices.
The team designed a SAM structure comprising two triphenylamine electron donors and one cyano-phosphonic acid electron acceptor. Compared with a simple non-"electronic resonance" monolayer, the anchoring group—the cyano-phosphonic acid moiety—exhibits a higher electron cloud density, thereby effectively enhancing the anchoring strength between the SAM and the substrate. As a result, the device stability under various harsh operating conditions, including wide-range temperature cycling from -40°C to 85°C and continuous illumination at 85°C, has been significantly improved, offering the potential to extend the application scenarios of perovskite solar cells to polar regions, space, and beyond.
Design of "Electronic Resonance" SAM for Enhanced Operational Stability of Devices Under Harsh Environments
This work reveals the intrinsic correlation between the anchoring strength of the SAMs and their electron cloud arrangement at a fundamental level, establishing a new paradigm for the design of "electronic resonance" monolayer structures. On the application front, the novel "electronic resonance" SAM achieved certified device efficiencies of 27.69% and 23.63% on small-area devices (0.063 cm²) and module devices (15.64 cm²), respectively. Encapsulated devices exhibited breakthrough improvements in operational stability under various stringent aging conditions. Furthermore, the universality of this SAMs design strategy has been reliably validated in flexible perovskite solar cell devices.
This cross-institutional collaborative effort represents an important original advancement in the field of perovskite solar cells in China. It provides a new underlying chemical design strategy for achieving stable operation of perovskite solar cell devices under harsh environmental conditions, thereby accumulating theoretical and technical foundations for the upgrading of China's new energy industry and the realization of the "carbon peaking and carbon neutrality" strategic goals.
Yaowen Li, Xiankai Chen, and Tiankai Zhang are the co-corresponding authors, while Xiaoxiao Wu and Wenwen Kou are the co-first authors of this paper.
