development of next generation of compact and flexible electronics. [1] The increase in computer usage and ever-growing dependence on cloud systems require better methods for dissipating heat away from electronic components. The important ingredients of thermal management are the thermal interface materials (TIMs). Various TIMs interface two uneven solid surfaces where air would be a poor conductor of heat, and aid in heat transfer from one medium into another. Two important classes of TIMs include curing and noncuring composites. Both of them consist of a base, i.e., matrix materials, and thermally conducting fillers. Commonly, the studies of new fillers for the use in TIMs start with the curing epoxybased composites owing to the relative ease of preparation and possibility of comparison with a wide range of other epoxy composites. Recent work on TIMs with carbon fillers have focused on curing composites, which dry to solid. [2][3][4][5][6][7] Curing TIMs are required for many applications, e.g. attachment of microwave devices, but do not cover all thermal management needs. Thermal management of computers requires specifically noncuring TIMs, which are commonly referred to as thermal pastes or thermal greases. They are soft pliable materials, which unlike cured epoxy-based composites, or phase change materials, remain soft once applied. This aids in avoiding crack formations in the bond line due to repeated thermal cycling of two connected materials with different temperature expansion coefficients. Noncuring TIMs also allow for easy reapplication, known as a TIM's reworkability property. Noncuring TIMs are typically cost efficient-an essential requirement for commercial applications. Various applications in electronics, noncuring grease-like (soft) TIMs are preferred. Examples of the applications include but are not limited to cooling of servers in large data centers [8] and personal devices which are the primary targets for these applications. Current commercially available TIMs perform in thermal conductivity range of 0.5-5 Wm −1 K −1 with combination of several fillers at high loading fractions. [9] State-of-the-art and next-generation electronic devices require thermal pastes with bulk thermal conductivity in the range of 20-25 Wm −1 K −1 . [10,11] This study focuses specifically on noncuring TIMs with graphene and few-layer graphene (FLG) fillers.Curing and noncuring TIMs consists of two main components-a polymer or oil material as its base and fillers, Development of next-generation thermal interface materials (TIMs) with high thermal conductivity is important for thermal management and packaging of electronic devices. The synthesis and thermal conductivity measurements of noncuring thermal paste, i.e., grease, based on mineral oil with a mixture of graphene and few-layer graphene flakes as the fillers, is reported. The graphene thermal paste exhibits a distinctive thermal percolation threshold with the thermal conductivity revealing a sublinear dependence on the filler loading. This behavior contrasts wi...
EM radiation. For this reason, the electronic components have to be protected from the intra-and inter-system EM radiations in order to avoid fast degradation and failure. [4-14] It has also been suggested that prolonged exposure to even nonionizing EM waves in the MHz and GHz frequency range may have detrimental effects on humans and other living beings making the EMI shielding important from safety perspectives. [15-19] The dense packing of the electronic components in the state-of-the-art 2D, 2.5D, and 3D integrated systems and generation of high heat fluxes create an environment with high temperatures, which adversely affect the efficiency and stability of the EMI shielding materials. [20,21] The absorption of EM waves results in the temperature rise of the material making the situation even worse. The data on the efficiency of the conventional and recent EM shield materials in most cases are limited to room temperature (RT) operation. [20-23] The latter is despite the fact that many new non-metallic materials, introduced for EMI shielding, suffer from thermal instability, oxidation, or significant reduction in the shielding efficiency at high temperatures. These concerns require development of novel multifunctional materials, which can serve concurrently as an excellent EM shields with the high thermal stability and conductivity at elevated temperatures. The ability of such materials to act as the thermal interface materials (TIMs) which can dissipate heat efficiently becomes a necessity rather than an extra bonus feature. [2,3,20,21,24] TIMs are applied between two solid surfaces in order to fill the microscopic voids at the interface, and enhance the thermal transport from a heat source to a heat sink. [25-27] The base materials for TIMs are amorphous polymers, which have low thermal conductivity, typically in the range from 0.2 to 0.5 Wm −1 K −1. [28] For this reason, the polymers used as base materials for TIMs are filled with highly thermally conductive fillers to enhance their overall thermal conductivity. The lowweight, mechanical stability, resistance to oxidation, flexibility, and ease of manufacturing are other important criteria for TIMs. EMI shielding materials block the incident EM waves by reflection and absorption mechanisms. Both mechanisms
Temperature rise in multi-junction solar cells reduces their efficiency and shortens their lifetime. We report the results of the feasibility study of passive thermal management of concentrated multi-junction solar cells with the non-curing graphene-enhanced thermal interface materials. Using an inexpensive, scalable technique, graphene and few-layer graphene fillers were incorporated in the non-curing mineral oil matrix, with the filler concentration of up to 40 wt% and applied as the thermal interface material between the solar cell and the heat sink. The performance parameters of the solar cells were tested using an industry-standard solar simulator with concentrated light illumination at 70× and 200× suns. It was found that the non-curing graphene-enhanced thermal interface material substantially reduces the temperature rise in the solar cell and improves its open-circuit voltage. The decrease in the maximum temperature rise enhances the solar cell performance compared to that with the commercial non-cured thermal interface material. The obtained results are important for the development of the thermal management technologies for the next generation of photovoltaic solar cells.
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