Linear Electron Beam Assisted Roll-to-Roll in-Vacuum Flexographic Patterning for Flexible Thermoelectric Generators

Abstract

In this work, we investigated the use of in-line linear electron beam irradiation (LEB) surface treatment integrated into a commercially compatible roll-to-roll (R2R) processing line, as a single fluorocarbon cleaning step, following flexography oil masking used to pattern layers for devices. Thermoelectric generators (TEGs) were selected as the flexible electronic device demonstrator; a green renewable energy harvester ideal for powering wearable technologies. BiTe/BiSbTe-based flexible TEGs (f-TEGs) were fabricated using in-line oil patterned aluminium electrodes, followed by a 600 W LEB cleaning step, in which the duration was optimised. A BiTe/BiSbTe f-TEG using an oil-patterned electrode and a 15 min LEB clean (to remove oil prior to BiTe/BiSbTe deposition) showed similar Seebeck and output power (S ~ 0.19 mV K−1 and p = 0.02 nW at ΔT = 20 K) compared to that of an oil-free reference f-TEG, demonstrating the success of using the LEB as a cleaning step to prevent any remaining oil interfering with the subsequent active material deposition. Device lifetimes were investigated, with electrode/thermoelectric interface degradation attributed to an aluminium/fluorine reaction, originating from the fluorine-rich masking oil. A BiTe/GeTe f-TEG using an oil-patterned/LEB clean, exceeded the lifetime of the comparable BiTe/BiSbTe f-TEG, highlighting the importance of deposited material reactivities with the additives from the masking oil, in this case fluorine. This work therefore demonstrates (i) full device architectures within a R2R system using vacuum flexography oil patterned electrodes; (ii) an enabling Electron beam cleansing step for removal of oil remnants; and (iii) that careful selection of masking oils is needed for the materials used when flexographic patterning during R2R.

Advances in flexible inorganic thermoelectrics

“…thermoelectric legs to impart overall flexibility to the device. 32,[211][212][213][214][215][216][217][218][219][220][221][222][223][224][225][226][227][228][229] Additionally, the use of small-sized solidstate inorganic thermoelectric materials as thermoelectric legs can provide relatively higher performance to the device, although their flexibility might be more limited. [230][231][232][233][234][235][236][237][238][239][240][241][242][243][244][245][246][247] Furthermore, the rational design of device structures and the use of appropriate flexible heat sinks are also important research focuses for designing vertically oriented F-TEDs.…”

“…Therefore, it is crucial to design F‐TEDs with a vertical‐like structure. In general, designing such F‐TEDs involves considering the use of flexible inorganic thermoelectric materials as thermoelectric legs to impart overall flexibility to the device 32,211–229 . Additionally, the use of small‐sized solid‐state inorganic thermoelectric materials as thermoelectric legs can provide relatively higher performance to the device, although their flexibility might be more limited 230–247 .…”

Exceptional Performance of Room Temperature Sputtered Flexible Thermoelectric Thin Film Using High Target Utilisation Sputtering Technique

“…[27][28][29][30] Thinfilm TE materials have attracted widespread attention since the performance of TE materials can be modified using nanostructure engineering, [31] by decoupling the TE parameters shown in Equation (1). By further integrating the vacuum deposition with a flexographic printing technique, [32][33][34] patterning of flexible thin-film materials can be achieved at a μm resolution in the plane.…”

Roll‐to‐Roll Patterning of Indium‐Tin‐Oxide Electrodes Using a Low‐Cost Laser‐Marking Machine

“…Although this machine has limitations, such as a restricted working area compared to that for a 3D printer-based laser machine, we believe that these drawbacks can be overcome using a continuous process such as a roll-to-roll (R2R) process. [22][23][24] This study presents a method for patterning ITO on flexible substrates using a commercially available low-cost laser-marking machine. The 1064-nm laser used in the study was effective in etching ITO; [25][26][27] however, it could potentially damage the surface of a polymer substrate.…”

“…Although this machine has limitations, such as a restricted working area compared to that for a 3D printer‐based laser machine, we believe that these drawbacks can be overcome using a continuous process such as a roll‐to‐roll (R2R) process. [ 22–24 ]…”