Manisha V. Rane-Fondacaro

Eutectic Mixtures of Ionic Liquids Electrolytes for Electric Double Layer Capacitors

Eutectic mixtures of oxygen-containing spirobipyrrolidiniumbased ionic liquids were investigated as prospective room temperature ionic liquid electrolytes (RTILs) for supercapacitor application. These in-house developed novel ionic liquids (IL) possess wide voltage window (6-7 V) and solubility (3-5.5 M) in conventional solvents, such as acetonitrile and propylene carbonate. The potential window of mixed RTIL was about 5.5 V (at 50 μA/cm threshold). The RTIL mixtures exhibit higher breakdown potential (> 4.6 V) as compared to conventional molecular solvent (acetonitrile)-based cells (~4.0 V) in supercapacitor tests. However, these RTIL mixtures (neat, i.e. w/o any solvent addition) lead to high equivalent series resistance (ESR) initiating around 3.9 V and lower capacitance. Cycling of the negative electrode at 4.6 V led to degradation of the active carbon material, while the positive electrode maintained its integrity.

Compatibility of the alternative seed layer (ASL) process with mono-Si and poly-Si substrates patterned by laser or wet etching

An alternative seed layer (ASL) process is proposed in order to increase the efficiency of silicon solar cells by forming a low cost, front metal contact with reduced contact resistance and increased line conductivity and aspect ratio. A nickel seed layer is deposited directly on silicon to form a low resistivity nickel silicide (NiSi) ohmic contact and this contact is thickened by light induced plating (LIP) of nickel and copper. Unlike the traditional screen printing process currently used in industry, the ARC layer must be patterned to expose the silicon surface for nickel deposition. This paper investigates the compatibility of the ASL process with two different ARC patterning methods: 1) masking & wet chemical etching, and 2) laser ablation. In addition, the ASL process is demonstrated on both mono-crystalline and polycrystalline silicon substrates with ARC layers from different sources. The nickel seed layer and resulting NiSi layer are evaluated using scanning electron microscopy (SEM) with energy dispersive x-ray spectroscopy (EDS) and focused ion beam (FIB) cross section. X-ray photoelectron spectroscopy (XPS) is used to investigate the completeness of the ARC removal step. In addition, contact resistance testing will be performed to determine the quality of the ohmic contact formed from the ASL process. The importance of chemistry optimization in the development of a robust ASL process that is compatible with mono-Si and poly-Si substrates and exposed to two different ARC patterning methods will be discussed.

Relationship of aluminum grain size to the grain size of polycrystalline silicon produced by the aluminum induced crystallization of amorphous silicon

The aluminum-induced crystallization and layer exchange process shows great promise for converting a-Si into large-grained poly-Si for solar cell applications. To investigate the relationship between the grain size of Al and the final grain size of poly-Si, a series of samples were deposited by RF magnetron sputtering 165 nm of Al onto SiN/SiO2 coated (100) silicon substrates. The Al grain size was varied by vacuum annealing prior to the deposition of 195 nm of a-Si. Completion of the layer exchange process resulted in poly-Si films which were then characterized with plan view TEM. The average Si grain size was found to increase as a function of increasing Al grain size, consistent with the grain-boundary nucleation model for this process. The largest average Si grain size of 4.9±1.92µm corresponded to the Al sample which was annealed for 24 hours at 550°C. The microstructure of the poly-Si film can therefore be manipulated by altering the properties of the as-deposited Al layer with an isothermal anneal.

Synthesis, Thermochemical, and Thermomechanical Characterization of High Conductivity 4-Azoniaspiro[3,4]octane Salts

Electrolytes based on the spiro-type quaternary ammonium salt, 1,10-spirobipyrrolidinium tetrafluoroborate (SBP BF4, 4-azoniaspiro[4.4]nonane tetrafluoroborate, Figure 1) are widely being investigated for electric double layer capacitor (EDLC) applications owing to their high conductivity. The SBP cation comprises two symmetric 5-membered rings joined together by a NC functionality. Replacing one of the 5-membered rings with a 4membered ring results in the 1-azetidyl-10-spiropyrrolidinium cation (AP, 4-azoniaspiro [3.4]octane, Scheme 1). The highest conductivity among all the quaternary ammonium salts has been reported for AP salts in several patents. However, there are no reports on a facile synthesis of AP salts nor on the thermochemical properties of high purity AP salts. In this paper, we report a novel method for the synthesis of AP salts (BF4, PF6 and NTf2), and compare and contrast properties of AP BF4, AP PF6, AP NTf2 with these of SBP BF4.