A cross-sectional schematic of the layers of a typical silicon heterojunction solar cell based on the p-i-n-i-n scheme. The metal fingers are electrodes that connect to the solar cell. The ITO (indium-tin oxide) acts as the antireflection coating as well as a conductor for lateral movement of charge carriers. The p+ and n+ doped amorphous layers are selective contacts that aid charge carrier separation and collection. The intrinsic amorphous layer and the crystalline silicon substrate together form the heterojunction. The intrinsic amorphous silicon provides surface passivation of the absorber. Only photons that are absorbed in the crystalline silicon substrate contribute to photocurrent. The zig-zag surfaces represents anisotropic texturing of the monocrystalline silicon surface. The silicon is etched by a base such as an alkali metal hydroxide or TMAH, forming pyramids which enhance light capture by reflecting outgoing light back onto the solar cell surface.
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