Tri-System-Integrated Systems for Ultra-Flexible Optoelectronic Devices with High Mechanical-Electrical-Humidity Stability

Flexible/foldable optoelectronic devices (OEDs) such solar cells (SCs) and light-emitting diodes (LEDs) have a lot of market potential for applications in photovoltaics and display integrated into buildings and wearable electronics. While perovskite and organic materials have become promising candidates for highly performed optoelectronic devices, mechanical flexibility of their OEDs extends applications in emerging flexible/ foldable electronics. Additionally, solution-processed flexible/foldable OEDs feature low cost, low carbon and low power consumption in production. However, electrodes of organic/perovskite OEDs such as widely adopted indium-tin-oxide (ITO) electrodes are formed by physical deposition methods (e.g., sputtering and thermal evaporation) which are high power consumption, large carbon footprint, and incompatible with high throughput production, thus hindering further development. Moreover, developing efficient flexible/foldable OEDs with super-flexibility (foldability) is still challenging due to the poor mechanical durability of typical ITO electrodes.

We recently developed an in-situ solution-processed method (iSPM) to achieve a new class of foldable transparent electrodes (FTEs) composed of metal-oxide nanoparticles (MONPs) and silver nanowires (AgNWs) through the unique tri-system integration including (i) AgNW-AgNW, (ii) MONP-MONP, and (iii) AgNW-MONP systems [1]. Based on the new electrode semi-embedded in colorless polymers such as polyimides, the foldable perovskite OEDs with very good stability against multi-loading (mechanical-electrical-moisture) operation with folding radius as small as 0.75mm, humidity 85% and continuous electrical bias operations have been demonstrated. To further improve device performances, we have introduced several strategies to the perovskites including reconstruction of subsurface lattice for stable perovskite [2-3]. The PCE of the perovskite SCs can reach 25.8% [3]. We will design the functional side-branches of ligands of perovskite nanocrystals (PeNCs) for enhancing the electrical conduction and optimizing the spacing between the ligand functional groups and the surface pattern of PeNCs, resulting in effective synergistic passivation effect and significant improvements in perovskkte LED efficiency and stability [4-7]. Meanwhile, through establishing ligand-termination surface structure on perovskites with anchoring points and polymeric soft chains on perovskites beyond the corresponding functional group-only or polymer-only strategies in reducing Young’s modulus, we demonstrated high efficiency and mechanical stable flexible perovskite LEDs [7]. In all, the efficiency and stability of the foldable/ultra-flexible red-green-blue perovskite LEDs can be significantly improved by comprehensively designing the ligand structures. Consequently, with the tri-system integrated electrodes, various high-performance organic/inorganic ultra-flexible OEDs have been demonstrated.

[1] J. Kim, W.C.H. Choy, et al, Nature Commun., 15, 2070, 2024; [2] Z.W. Gao, W.C.H. Choy, et. al, Joule 8, 1, 2024; [3] Z.W. Gao, W.C.H. Choy, et. al, Nature Photonics, accepted. [4] B. Lyu, W. Choy, et. al., ACS Energy Lett., 8, 577,2023; [5] D. Li ,W. Choy, et. al., ACS Energy Lett., DOI:acsenergylett.4c00881; [6] B. Lyu, W. Choy, et. al., Angewandte Chemie, in press; [7] C. Liu, W. Choy, et. al., Adv. Funct. Mater., 2024, 2404791.