Continuous in-line hot-wire chemical vapor deposition of thin film silicon p-i-n solar cells

Abstract

This contributions describes the successful implementation of a novel method for in-line continuous deposition of a-Si:H p-i-n solar cells by Hot Wire Chemical Vapour Deposition (HWCVD). As HWCVD does not use RF power supplies, there are no high frequency electromagnetic fields, and thus, scaling up is not hampered by finite wavelength effects or rigorous requirements to avoid inhomogeneous electrical fields. The hot catalytic wire in HWCVD is a linear source of radicals mounted perpendicular to the transport direction. We demonstrate the homogeneous in-line deposition of HWCVD solar cells on upward-facing substrates. The downward, dust-free deposition of thin film silicon greatly simplifies the mounting of the substrates, which can either be rigid or a flexible web, for in-line manufacturing at reduced cost. Amorphous (protocrystalline) as well as nanocrystalline silicon thin films with device-quality properties have been achieved on moving substrates. The local deposition rate is relatively high, at 1 nm/s, and a linear speed up to 30 cm/min has been used to produce device-quality i-layers with protocrystalline nature. We have recently further improved our thus deposited p-i-n solar cells to 8.3% efficiency (despite air breaks after the p-layer and before the n-layer). The potential for high deposition rate and fast roll-to-roll deposition is also discussed.