Study Of The Front Side Electrode Metallization Of Silicon Solar Cells

Crystalline silicon solar cells has dominated the market share in solar cells industry due to its high energy conversion efficiency. However, the big challenge for the crystalline silicon solar cells is the production costs and achieving the high energy conversion efficiency. The cost of crystalline silicon solar cells have three main parts: the aluminum back electrode, crystalline silicon and silver front side electrode, among them the Ag front side electrode costs10%to20%of the whole device. In order to reduce the production costs, Cu is used as the gate electrode material of the front lines of crystalline silicon solar cells due its excellent conductivity and cheap price.In our previous work, direct Light Induced-Plating (LIP) Cu front side electrode without laser grooving had been proposed. For this proposal, the key part is to obtain the uniform coverage of metal on crystalline silicon solar cells by Light Induced-Plating which has been also performed as the diffusion barrier layer and adhesive layer for copper electrode. To address the issues, the key is to understand these questions:How to form an uniform coverage of the metal layer directly on the semiconductor? what factors will affect the process of the LIP?For the directly LIP metal on crystalline silicon solar cells, it will involve the solution/semiconductors interface, particularly the relative position of the Fermi level of the semiconductor and the equilibrium potential of solutions. Moreover, the metal direct on the semiconductor is also performed as the diffusion barrier to prevent the Cu atom diffusion into the silicon to form the recombination centers in the PN junction, which will seriously reduce the silicon solar cells photovoltaic conversion efficiency and its lifetime. Co has a lower diffusion rate in Si and could form excellent good ohmic contact after Rapid Annealing Process (RTP). Hence, Co was chosen as the Cu atoms diffusion barrier materials. In this thesis, we had systematically studied the different metals plated on the semi-finished crystalline silicon solar cells by LIP. The alignment of the Fermi level of the semiconductor and the equilibrium potential of the metal ion had been studied by the cycle voltammetry, the electrochemical impedance spectroscopy and the absorption spectra of the electrolyte. The factors affecting the plating rate of LIP had been summarized. Finally the uniform and dense layer of the cobalt, nickel, zinc and bismuth metal had been further obtained and examed by(SEM, XRD), among them, the cobalt layer has excellent adhesion properties on the silicon substrate of solar cells. It also had been demonstrated that the cobalt and silicon can form ohmic contact after RTP, and an uniform CoSi2layer with excellent conductivity can be obtained by controlling the annealing temperature. Thus, Co has the advantages as the diffusion and adhesion layer between Cu electrode and silicon.Moreover, without the laser grooving and the lithography, the front electrodes had been formed by only light patterning and light induce plating. As demonstration, we had successfully fabricated patterned Co electrodes with15grid lines and a width of1mm on3cm*3cm crystalline silicon solar cell substrate. After RTP, Cu electrodes were plated immediately on the Co grid lines. Finally, a new front electrode structure Si/CoSi2/Co/Cu was obtained. Thus, we had further demonstrated the directly LIP Cu technology for the application in the front contact electrodes of the crystalline silicon solar cell.Our work will benefit the future development of the Cu front side electrode metallization for crystalline silicon solar cell and provide a new route to form a diffusion barrier layer on the semiconductor.