Silicon films for heterojunction solar cells by hot-wire CVD

Using hot-wire chemical vapor deposition (HWCVD), an attractive alternative to the established plasma-enhanced chemical vapor deposition (PECVD), we aim to deposit silicon films for silicon heterojunction (SHJ) solar cell applications. Because of the absence of energetic particles in HWCVD, the layers grow softly and free of damage, hence promising excellent surface passivation and therefore highly efficient solar cells. We report the investigation of intrinsic silicon films, acting as passivation layers, by adjustment of the deposition parameters, with a focus on the substrate temperature as the most important factor. Passivation layers, prepared with differing deposition parameters, were characterized by measurement of the minority-carrier lifetimes using the photoconductance method. At 6 nm a-Si:H thickness, average minority-carrier lifetimes of 1.2 ms were obtained on textured substrates. By combining the optimized HWCVD passivation films and doped silicon films deposited by PECVD, cell efficiencies of 19.7% were achieved. By also depositing the n- und p-doped a-Si:H films by HWCVD cell efficiencies above 18.2% were obtained on a 145 x 145 mm2 cell area.