The study on black silicon solar cells using the high density multi-hollow cathode plasma system

This paper deals with the investigation on formation of microstructures on silicon surface using reactive ion etching (RIE) in a multi-hollow cathode system (Fig. 1). This reactor consists of a Pyrex tube defining the vacuum chamber, with the outer metal cylindrical electrode (grounded) acting as a counter electrode for the aluminum plate electrodes assembly which is in electrical contact with silicon wafers. The plate electrodes have a diameter of 150 mm each. These electrodes are electrically and structurally connected by metal supports, close to their outer rim, with a separation space of 25 mm between each of them. The Pyrex tube has an inner diameter of 190 mm. RF power applied to the electrodes creates an electrical field on their surfaces and causes an excitation of reactive gases in the space between them, preferably between the silicon wafers. This produces a high level of ionization of the gas and dense plasma therein due to the repelling movement of the entrapped electrons between the powered electrodes; and this is called the hollow cathode effect. In this work, optogalvanic (OG) signal is used to analysis the variation of plasma conductivity caused by the absorption of radiation at a certain spectral transition of the plasma medium. The OG effect technique was developed for the purposes of laser spectroscopy and has been used to diagnose plasma parameters such as, the ionization rate, atomic density and translational temperature of the plasma. The multi-hollow cathode plasma system used in the present work generated plasma ion density up to 2x 10 ¹²cm^-3 (Fig. 2). Plasma texturing has been shown to produce black silicon surfaces with almost zero reflectance. The silicon surface was covered with columnar microstructures each having diameter ranging from 50 to 100 nm and depth of about 500 nm. Solar cells with efficiencies 11. 7% and 10.2% were fabricated using black c-Si and black mc-Si wafers respectively by making use of industrial mass production line system.