Inductively coupled plasma chemical vapour deposited AlOx/SiNy layer stacks for applications in high-efficiency industrial-type silicon solar cells

Abstract

Passivated emitter and rear cells (PERC) are considered to be the next generation of industrial-type screen-printed silicon solar cells. Deposition methods for rear passivation layers have to meet both the high-throughput and low-cost requirements of the PV industry in combination with high-quality surface passivation properties. In this paper, we evaluate and optimise a novel deposition technique for AlOx passivation layers by applying an inductively coupled plasma (ICP) plasma-enhanced chemical vapour deposition (PECVD) process. The ICP AlOx deposition process enables high deposition rates up to 5nm/s as well as excellent surface recombination velocities below 10cm/s after firing. A fixed negative charge of −4×1012cm−2 is measured for ICP AlOx single layers with an interface state density of 11.0×1011eV−1cm−2 at midgap position. When applied to PERC solar cells the ICP AlOx layer is capped with a PECVD SiNy layer. We achieve independently confirmed conversion efficiencies of up to 20.1% for large-area (15.6×15.6cm2) PERC solar cells with screen-printed metal contacts and ICP AlOx/SiNy rear side passivation on standard boron-doped Czochralski-grown silicon wafers. The internal quantum efficiency reveals an effective rear surface recombination velocity Srear of (90±30)cm/s and an internal rear reflectance Rb of (91±1)% which demonstrates the excellent rear surface passivation of the ICP AlOx/SiNy layer stack.