Material Requirements for Buffer Layers Used to Obtain Solar Cells with High Open Circuit Voltages

This paper discusses material requirements for junction layers needed to obtain solar cells with highest possible open-circuit voltages (VOC). In a typical a-Si:H-based 'p/i/n' solar cell, this includes the transparent conductive oxide (TCO) contact layer, the p-layer, a 'buffer layer' inserted at the p/i interface, and the surface portion of the intrinsic layer. In HIT-cells, the i-layer between(n-type) c-Si and (p-type) a-Si:H may be regarded as the buffer. Our suggestion to obtain high values of VOC relies on using materials with high lifetimes and low carrier mobilities that are capable of reducing surface or junction recombination by reducing the flow of carriers into this loss-pathway. We provide a general calculation that supports these approaches and can explain why theseschemes are beneficial for all solar cells.