Hydrogenated Aluminum Doped Zinc Oxide as Highly Transparent and Passivating Indium-Free Recombination Junction for TOPCon-Based Bottom Cell

TL;DR

This study demonstrates that hydrogenated aluminum-doped zinc oxide (AZO:H), deposited via spatial atomic layer deposition, is a highly transparent, passivating, and indium-free material suitable for recombination junctions in tandem solar cells, offering a promising alternative to ITO.

Contribution

The paper introduces AZO:H deposited by spatial ALD as a novel, indium-free recombination junction material with excellent optical and passivation properties for TOPCon-based bottom cells.

Findings

AZO:H films exhibit over 90% transparency in 380-1200 nm range.

Stack with AZO:H and AlOx capping achieves up to 734 mV iVoc after annealing.

AlOx layer enhances thermal stability and passivation quality.

Abstract

Tandem solar cells offer a promising alternative to exceed the efficiency limits of single-junction silicon photovoltaics, yet they require high-performance recombination junctions that are transparent, passivating, and electrically efficient. Indium tin oxide (ITO), which is conventionally used as a recombination junction material, faces challenges related to indium scarcity and sputter-induced damage. This work investigates hydrogenated aluminum-doped zinc oxide (AZO:H) deposited by spatial atomic layer deposition (s-ALD) as a viable indiumfree alternative for TOPCon-based bottom cells. The deposited AZO:H films demonstrate excellent transparency, exceeding 90% in the 380-1200 nm wavelength range. When applied to n-TOPCon surfaces with an AlOx capping layer, the stack achieves an outstanding passivation quality, indicated by implied open-circuit voltage (iVoc) values up to 734 mV after annealing. The AlOx capping layer proved crucial for enhancing thermal stability by preventing hydrogen effusion at higher temperatures. While the contact resistivity was high for the 20 nm thick films tested, the combination of superior optical and passivation properties establishes spatial ALD-deposited AZO:H as a highly promising material for creating efficient and indiumfree recombination junctions in next-generation tandem solar cells.