Abstract
Although silicon solar cell is discovered more than 50 years, the chase on raising high efficiency as well as improving fabrication technology continuous. During the process of front metallization, electroless plating of nickel/copper bi-layer an alternative for conventional srcreen-printing silver past is one of important technical goal. However, it is revealed that the physical adhesion between electroless plating nickel layer (ELS/Ni) and silicon (Si) wafer is too weak to provide adequate contact. Therefore in this study, we aim to improve the physical adhesion as well as electrical contact of ELS/Ni on Si wafer. In particular, we attempt to modify Si wafer surface with silane compound and then utilize a novel, self-developed nano-palladium particle catalyst (Polyvinylpyrrilidone Capped Palladium, PVP-Pd); the PVP-Pd is found to have molecular-level interaction with the functional groups on the silane compound and consequently provide better macroscopic adhesion. In the first part, we focus on the effect of silane compound modification which is examined by contact angle measurements, fluorescent labelling, as well as atomic force microscope (AFM). In addition, the fourier-transform infrared spectrometer (FTIR) is applied to explain the effect of post-sonication on silane-modified Si surface. The second part of this study is to examine the adhesion and contact resistance between ELS/Ni layer and Si wafer. All of the sample prepared by ELS/Ni (shows comparable film thickenss of ~ 0.2μm for a depositon time of 1 minute). As to the adhesion test, the result shows that the best adhesion value of 11 MPa is found in the sample using 100ppm PVP-Pd on silane-modified silicon surface without the need of post rapid thermal annealing (RTA), which is much higher than the sample made of commercial Sn/Pd catalyst (2.57 MPa). To explain this improvement, X-ray photoelectron spectroscopy (XPS) is applied results to understand the interaction between sialne compound and PVP-Pd particle. Meanwhile, we also try to measure the specific contact resistance between the ELS/Ni and Si wafer. According to the transmission line model (TLM) method and proper pattern on the sample, an acceptable value of 0.0532 ohm．cm2 is measured in the sample using 50ppm PVP-Pd on silane-modified Si surface without RTA, which is one third of the sample using commercial catalyst.