Optimization of a-Si:H p-i-n solar cells through development of n-layer growth evolution diagram and large area mapping

A growth evolution diagram has been developed to guide plasma-enhanced chemical vapor deposition (PECVD) of n-type hydrogenated amorphous silicon (a-Si:H) and nanocrystalline silicon (nc-Si:H) for use as the n-layer component of p-i-n a-Si:H superstrate solar cells. The substrates for such growth evolution diagram development by real time spectroscopic ellipsometry (RTSE) are crystalline silicon wafers that have been over-deposited with intrinsic a-Si:H layers. This diagram was applied to guide n-layer depositions on 15 cm × 15 cm glass/TCO/p/i superstrates in order to relate the diagram to the performance parameters of single-junction a-Si:H solar cells. Over the 15 cm × 15 cm TCO coated glass superstrate area, a 16 × 16 array of p-i-n dot cells has been fabricated, and this area has been mapped at high resolution by spectroscopic ellipsometry (SE). Analysis of such SE data over the full area provides maps of the p-layer effective thickness, i-layer thickness and band gap, and n-layer thickness and nanocrystalline Si:H vol. fraction. In addition, J-V measurements were performed on the 16 × 16 array of dot cells. The goal of this study is to identify and understand the relationships between basic materials property and thin film solar cell performance variations over large areas, and to evaluate impacts of non-uniformities on module performance.