Photovoltaic Response of Silicon Wafers Treated in the K ₂ WO ₄ -Na ₂ WO ₄ -WO ₃ Melt

Abstract

Texturing silicon wafers is one way to increase the performance of solar cells. This work is the first to report on the surface modification of Si wafers by processing in polytungstate melts. Scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction analysis (XRD), the Brunauer–Emmett–Teller (BET) method, and photoelectrochemical measurements were used to elucidate the effect of texturing conditions in the Na 2 WO 4 —K 2 WO 4 (1:1) melt containing 35 or 50 mol% WO 3 at 973 K in air. As a result of cathodic treatment in the melt containing 50 mol% WO 3 at the potential of –0.92 V (vs Pt) for 15 s, upright pyramids were formed on the Si surface. In addition, inverted pyramids appeared at the OTB/Si contact points. The photocurrent density of these samples was several times higher than that for the initial Si wafer or the Si wafer etched in 5 M NaOH solution at 353 K for 20 min. Mechanisms for the formation of upright and inverted pyramids were proposed. Unusual eight-faceted pyramids were formed on the Si surface during cathodic treatment in the melt containing 35 mol% WO 3 at –1.19 V for 15 s, but the photocurrent density of such samples was low.