Silicon(Si) is definitely one of the most important electronic materials. Until now, its solid and gas phases have been utilized as material sources while a liquid phase left almost unexplored. When the future sustainable industry is considered, however, a new process using liquid Si sources would be very attractive for the effective use of energy and material. As the first step of the practical use of liquid Si, we have developed a solar cell. Recently we succeeded to make a prototype and

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... strated its operation [1]. Here we will introduce four crucial points picked up among the various field ranging from raw material to device. (1) Synthesis of a SiH polymer solution (liquid silicon) and analysis of its solution state Cyclopentasilne(CPS)[2], which is a stable molecule (Si 5 H 10 ) having a boiling temperature of 194 deg C, undergoes ring opening polymerization by UV light to become polydihydrosilane. We found a good solvent for polydihydrosilane so that polymerization process can be traced in terms of molecular weight change by SEC-MALLS system (SEC:size-exclusion chromatography, MALLS: multi-angle laser light Scattering) [3]. Fig.1 shows the polymerization process during irradiating the 365nm UV light with 1mW/cm2 up to 240 min. Synthesized polymer was diluted by an organic solvent to get a polymer solution or liquid silicon. To investigate its solution state, the relationship among three parameters, intrinsic viscosity [η], radius of gyration Rg and molecular weight, was deduced based on the scaling rule. It is found that polydihydrosilane tends to have a branched structure like nano particles[3]. (2) Coating liquid silicon on the substrate [4] It was found that coating property of liquid silicon was totally governed by van der Waals interaction. To understand the coating phenomena, Hamaker constants of CPS, polydihydrosilane and solvents were measured by the SSM(simple spectral method) method [5] . Fig.2 shows the spin-coating result on the several substrates of which Hamaker constant are different each other. The liquid silicon used was a 1.5wt% polydihydrosilane solution in cyclooctan solvent. It clearly demonstrated that the larger Hamaker constant gave the better coating property, especially when the Hamaker constant is minus, the coated film broke during solvent drying to become a dot scattered structure. (3) Transformation from polydihydrosilane to an amorphous Si (a-Si) film [6] Different from an a-Si:H film from gas deposition, the film formation process using liquid silicon is a subsequence one from breaking of chains of polydihydrosilane, desorption of gases and formation of three dimensional Si-Si network. To grasp a picture view of the process, TG and DTA Figure 1. Change of Molar mass distribution by SEC-MALLS for CPS and polydihydrosilane synthesized with irradiation time 30, 60 and 240 min dissolved in cyclohexene at 25 degree C. Figure 2. Optical micrographs of polydihydrosilane films on different substrates.The A ALS values calculated by the SSM are noted on each micrograph. The length of the bar in each image is 100 µm. Figure3. TG (bold solid line), DTA (thin solid line), and DTG (dashed line) curves of polydihydrosilane. -1 0 0 5 -E x t e n d e d A b s t r a c t s o f t h e 2 0 1 2 I n t e r n a t i o n a l C o n f e r e n c e o n H -4 -1 ( I n v i t e d )