Thermal management problems in high-power flexible electronics are exacerbated by the design complexity and requirement of stringent temperature control to prevent skin burns. Thus, effective heat dissipation methods applicable to flexible electronics on polymer substrates are an essential device design component. Accordingly, this study investigates the pool boiling heat transfer characteristics and potential enhancements, enabled by laser-induced graphene (LIG), which is both highly porous and bendable. Patterned LIG with a mesh spacing of 200 μm was formed on flexible polyimide substrates by laser direct writing, and the resulting surfaces exhibited enhanced heat transfer characteristics. Pool boiling experiments were conducted with an FC-72 working fluid to investigate the heat removal capability of LIG, and its performance was further improved by separating the liquid supply passages from the vapor escape routes. Overall, the inclusion of LIG resulted in a 2- to 3-fold increase in both the critical heat flux (33.6 W/cm2) and heat transfer coefficient (7.6 kW/(m2·K)), compared to pristine polyimide films.

We developed a superhydrophobic surface using surface texturing with nano-sized structure and polytetrafluoroethylene (PTFE) film deposition. The properties of superhydrophobic surface were investigated using water contact angle, root mean square (RMS) roughness, and X-ray photoelectron spectroscopy (XPS). The contact angle of a water droplet was greater than 150°, which means extremely low wettability is achievable on superhydrophobic surfaces. For nano-sized structure, we carried out two step etching process using reactive ion etching (RIE) in a large pyramid substrate by potassium hydroxide (KOH) solution. Metal mesh installed RIE etched silicon substrate using SF 6 and O 2 gas. PTFE films were deposited by conventional RF magnetron sputtering. This process is applicable for stable superhydrophobic and selfcleaning surfaces due to hierarchical structures formed silicon wafer etched by RIE technique.

We have developed a new texturing method by forming a pyramidal black silicon structure using a metal mesh in the reactive ion etching (RIE) system in order to overcome the disadvantages of the texturing process using wet etching and the drawbacks of the needle(grass)-like black silicon. For the formation of a pyramidal black silicon on the silicon surface, the RIE system is modified to be equipped with a metal mesh on top of the head shower. The parameters for the RIE process are SF 6 /O 2 gas flow of 15/15 sccm, RF (radio frequency) power of 200 W, pressure of 50-200 mTorr, temperature of 5 8C, and process time of 5-20 min. An increase in the processing time increases the width of the pyramid; however, the height remains at 0.8 AE 0.1 mm for 15-20 min of processing. The crystalline wafer surface of the pyramidal black silicon of approximately 1.7 AE 0.2 mm width and at 0.8 AE 0.1 mm height in size is textured using the RIE system with 10.7% of reflectivity. Thus, the pyramidal black silicon and the RIE process using a metal mesh are superior to the conventional texturing structures and methods, respectively.

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We have developed nanosized structures on a silicon surface by the reactive ion etching method. The purpose of this work is to fabricate pyramid-nanocolumn structures for crystalline silicon solar cells using a reactive ion etching (RIE) system with a metal mesh and to simulate surface texturing structures using the PC1D program. The reflectance of the structures was lower than that of only-pyramid or only-nanocolumn structure arrays. We formed micropyramids by general anisotropic saw damage removal (SDR) etching using potassium hydroxide (KOH) solution, as well as nanocolumn structures by RIE with a metal mesh and SF6/O2 gas (35/30 sccm). We studied the fundamentals and morphologies of structures (micropyramids, nanocolumn structures, and pyramid-nanocolumn structures). Owing to anisotropic SDR etching in KOH solution for a single-crystalline silicon wafer, the whole wafer surface is covered with pyramid structures with a size range of 1–5 µm. After RIE texturing, nanocolumn structures with a size range of 20–50 nm were formed on the pyramid structures. Owing to binary surface texturing with pyramid and nanocolumn structures, spectra with weighted average reflectances below 3% in the wavelength range from 350 to 1100 nm were obtained under optimized condition. In particular, the average reflectance was 1.16% in the wavelength range of 400 to 1000 nm without an antireflection coating (ARC). The combination of the pyramid and nanostructures has a very low reflectance. Therefore, ARC is not required in the solar cell process in the case of using pyramid-nanocolumn structures.