Specific Contact Resistance Measurement of Screen-Printed Ag Metal Contacts Formed on Heavily Doped Emitter Region in Multicrystalline Silicon Solar Cells

Abstract

Multicrystalline silicon (mc-Si) wafers are widely used to develop low-cost high-efficiency screen-printed solar cells. In this study, the electrical properties of screen-printed Ag metal contacts formed on heavily doped emitter region in mc-Si solar cells have been investigated. Sintering of the screen-printed metal contacts was performed by a co-firing step at 725°C in air ambient followed by low-temperature annealing at 450°C for 15 min. Measurement of the specific contact resistance (ρc) of the Ag contacts was performed by the three-point probe method, showing a best value of ρc = 1.02 × 10−4 Ω cm2 obtained for the Ag contacts. This value is considered as a good figure of merit for screen-printed Ag electrodes formed on a doped mc-Si surface. The plot of ρc versus the inverse of the square root of the surface doping level (Ns−½) follows a linear relationship for impurity doping levels Ns ≥ 1019 atoms/cm3. The power losses due to current traveling through various resistive components of finished solar cells were calculated by using standard expressions. Cross-sectional scanning electron microscopy (SEM) views of the Ag metal and doped mc-Si region show that the Ag metal is firmly coalesced with the doped mc-Si surface upon sintering at an optimum firing temperature of 725°C.