Light-Induced Electrochemical Deposition of Ni for Si Solar Cell Processing

Abstract

This work outlines the general electrochemical features of the Ni light-induced deposition process. Typical observations for the deposition on textured solar cells are discussed and compared to planar n-Si (100) electrodes. The electrochemical measurements clearly show that after nucleation, Ni-on-Ni deposition is favored over Ni-on-Si, resulting in hemispherical growth. This observation is attributed to a kinetic effect and may be a disadvantage for the growth of ultra-thin contacting layers. In addition, the simultaneous metallization of fingers and busbars shows a significant non-uniformity due to an inevitable variation in current distribution which leads to an enhanced deposition rate for the narrowest features.The front side metallization of industrial silicon solar cells is currently based on screen printed silver (Ag) contacts which are fired through the front anti-reflection coating (ARC). One of the disadvantages of producing conductive lines with this method is that the resistivity of these lines is high as compared to bulk metal, mainly due to the use of glass based filling materials. 1 The fact that Ag contributes significantly to the costs of the metallization process and the troublesome printing of narrow lines, induced the development of alternative routes. 2 More recently, alternative processes are being developed that use a metal silicide as contacting layer and Cu as the main conductor. 3 In previous work we reported on the development of a relatively simple metallization scheme for crystalline silicon solar cells consisting of: 1) defining the front-contact pattern by laser ablation of the ARC; 2) deposition of Ni/Cu/Ag in a single plating sequence; and, finally, 3) sintering in N 2 for nickel silicidation. 4 Upon sintering, a low-resistivity, Ohmic contact is formed which enables the use of optimum, lowly-doped homogeneous emitters. 5 Cu serves as electrical conductor and the Ag (or Sn) capping layer enables the soldering of the individual cells, during panel assembly.Unlike the more expensive physical vapor deposition (PVD) techniques, electrochemical metallization allows for self-aligned deposition, i.e. deposition occurs selectively on areas where the semiconductor is exposed to solution. A common technique used for depositing contact layers is light induced plating (LIP). 6-9 So far, little attention has been focused on the (photo)electrochemistry of the solar cell metallization process. In this letter we discuss the basic electrochemistry of n-type Si (100) in nickel-containing solutions and light-induced deposition on pyramid-textured silicon solar cells. The implications of kinetic effects during contact/seed layer deposition are discussed. ExperimentalFor the Ni bath a nickel sulphamate solution (Rohm and Haas) and boric acid (Merck, p.a. grade) was used. The concentration was fixed to 0.62 M for both components. The pH of the solution was 3.9.The electrochemical measurements were performed using a standard three-electrode setup with the Si substrate as the working electrode, a Pt cou...

A novel method to prepare ZnO/Ni multilayer thin film used in back electrode for solar cell

“…Moreover, the Ni coating could greatly enhance the photoelectric current density of the back electrode due to its excellent conductivity. Meanwhile, a good ohmic contact is formed between nickel and the semiconductor [13]. Zinc oxide is often used in preparing the back electrode because of the chemical stability and low cost, and the active intrinsic layer of the light adsorption for solar cell can be made thinner to reduce the Staebler-Wronski (SW) effect [14].…”