Effects of texturing on the CV analysis of silicon solar cells

Abstract

Surface texturing is essential for obtaining solar cells with high efficiency. In crystalline silicon (c-Si) solar cells, low concentration alkaline solutions such as KOH and NaOH are commonly used to wet etch the surface and form random textures [1]. In the case of (100) silicon wafers, this exposes intersecting slow etching {111} planes forming a pyramidal shape. The height of the pyramids varies between 1 um to 4 um. This wafer with its random pyramidal texture is then exposed to a Phosphorus diffusion process to form the n-type emitter. The resulting PN junction is thus microscopically rough with the pyramidal texture. Caution must be exercised when analyzing the standard Capacitance-Voltage (CV) analysis to determine the base doping density. As reported in [2], the base-dopant concentration cannot be determined correctly without taking texture enhanced surface area into account. That work suggested a capacitance correction factor based on the geometry of the pn junction. In this work, we examine how surface texture affects CV analysis with the assistance of a commercial device simulator, Sentaurus [3]. The conditions for which the analytical formulas proposed in [2] is valid are clarified.