Application of the chemical vapor-etching in polycrystalline silicon solar cells

This paper reports a study of the application of chemical vapor-etching (CVE) for the rear surface and in the emitter of polycrystalline silicon (pc-Si) solar cells. The CVE technique consists of exposing pc-Si wafers to a mixture of HF/HNO3. This technique is used to groove the rear surface of the pc-Si wafers for acid vapors rich in HNO3 (HNO3/HF > 1/4), in order to realize rear-buried metallic contacts (RBMC) and the formation of a porous silicon (PS) layer on the frontal surface of the cell for volume ratio of HNO3/HF = 1/7. A significant increase of the spectral response in the long wavelength range was observed when a RBMC is formed. This increase was attributed to the reduction of the effective thickness of the base of the cells and grain boundary Al gettering. The achievement of a PS layer on the emitter of the pc-Si cells passivates the surface and reduces the reflectivity. The dark I–V characteristics of pc-Si cells with emitter-based PS show an important reduction of the reverse current together with an improvement of the rectifying behaviour. The I–V characteristic under AM1.5 illumination shows an enhancement of both short circuit current density and fill factor. The internal quantum efficiency is improved, particularly in the short wavelengths region.