Achieving High Power Density and Long‐Term Stable Flexible Triboelectric Nanogenerators through Surface Functionalization of High Work‐Function Electrode with Cationic Thiol‐Based Self‐Assembled Monolayer

Abstract

In this study, a reliable strategy is demonstrated to improve performance and stability of a triboelectric nanogenerator (TENG) by using cationic (11‐mercaptoundecyl)‐N,N,N‐trimethylammonium bromide (MUTAB) self‐assembled monolayer (SAM) as the surface modification layer for high work‐function (WF) Ag electrode. The thiol head group of MUTAB can form covalent bond to Ag surface, while the positively charged ammonium group can induce favorable surface dipole moment to lower the WF of Ag layer, enabling efficient charge transfer from Ag electrode to polydimethylsiloxane (PDMS) dielectric layer. This strategy is highly compatible with large‐area flexible TENG based on solution‐processed Ag nanoparticle layer, affording open‐circuit voltage (Voc) of 1008 V, short‐circuit current (Isc) of 124.9 µA, and power density of 39.4 W m−2. To the best of our knowledge, such remarkable power density represents the highest value ever reported for SAM‐modified TENG. Taking advantage of high output characteristics of flexible TENG, 328 light‐emitting diodes can be lit up instantaneously. More encouragingly, the resulting TENG also possesses good stability, maintaining ≈96% of its original Voc after 300 000 cycles of continuous testing. The present findings highlight the importance of surface modification with SAM for efficient and long‐term stable TENG, which can advance the development of intelligent self‐powered systems.

Charge transport through molecular ensembles: Recent progress in molecular electronics

“…Additionally, SAMs of substituted aliphatic molecules have been used to functionalize surfaces for triboelectric nanogenerators (TENG). 271 Recently, Cheng et al 272 used cationic thiol-based SAMs to effectively manipulate the work function of Au substrates, enabling efficient TENG output characteristic. In their previous work, the authors also used fluorinated aliphatic molecules with trichlorosilane termini group, which upon treatment, forms a robust SAM on a PDMS or Al surface, showing long-term stability and highest output performance of these SAM-based TENG devices.…”

Surface engineering of PDMS for improved triboelectrification

“…28,29 SAMs are ordered assemblies of organic molecules which can be covalently linked to various oxide, metal and polymer surfaces. Different polymers have been employed as substrates for SAM functionalization, such as polydimethylsiloxane (PDMS) 30–32 and polyethylene terephthalate (PET). 32–34 Most often TENGs are constructed using both PDMS and metallic electrodes modified by SAMs as contact layers.…”

“…32 Notably, fluorine-terminated SAMs on PDMS in combination with an ammonium bromide terminated SAM on a Ag electrode reached a power density of 39.4 W m −2 . 30 Regarding TENGs using polymers as both contact layers, Shin et al demonstrated that a TENG reaching a power density of 55 W m −2 can be constructed using two differently modified PET contact layers – one with an amine-based SAM and the other with a halogen-based SAM. 33…”

Ultrahigh power output and durable flexible all-polymer triboelectric nanogenerators enabled by rational surface engineering

“…11,17–21 For instance, we have demonstrated the feasibility of using self-assembled fluorinated molecules as the surface modification layer for PDMS, thereby significantly improving the TENG performance while maintaining excellent durability. 23–25 Despite this fact, TENGs based on existing surface modification layers are still mostly constrained by the rigid substrate. In addition, an adhesion problem between the triboelectric layer and the surface modification layer is usually observed.…”