Exploring co-sputtering of ZnO:Al and SiO2 for efficient electron-selective contacts on silicon solar cells

TL;DR

This paper demonstrates that co-sputtering ZnO:Al with SiO2 creates effective electron-selective contacts for silicon solar cells, achieving high efficiency and revealing key parameters for optimizing device performance.

Contribution

It introduces a novel AZO:SiO2 co-sputtered film as an electron-selective contact, achieving record efficiency with simplified fabrication.

Findings

Optimal AZO:SiO2 thickness is 2 nm for best performance.

The VOC is insensitive to AZO:SiO2 work function at optimal thickness.

Achieved 19.5% efficiency with AZO/Al contact.

Abstract

In recent years, considerable efforts have been devoted to developing novel electron-selective materials for crystalline Si (c-Si) solar cells with the attempts to simplify the fabrication process and improve efficiency. In this study, ZnO:Al (AZO) is co-sputtered with SiO2 to form AZO:SiO2 films with different SiO2 content. These nanometer-scale films, deposited on top of thin intrinsic hydrogenated amorphous silicon films and capped with low-work-function metal (such as Al and Mg), are demonstrated to function effectively as electron-selective contacts in c-Si solar cells. On the one hand, AZO:SiO2 plays an important role in such electron-selective contact and its thickness is a critical parameter, thickness of 2 nm showing the best. On the other hand, at the optimal thickness of AZO:SiO2, the open circuit voltage (VOC) of the solar cells is found to be relatively insensitive to either the work function or the band gap of AZO:SiO2. Whereas, regarding the fill factor (FF), AZO without SiO2 content exhibits to be the optimal choice. By using AZO/Al as electron-selective contact, we successfully realize a 19.5%-efficient solar cell with VOC over 700 mV and FF around 75%, which is the best result among c-Si solar cells using ZnO as electron-selective contact. Also, this work implies that efficient carrier-selective film can be made by magnetron sputtering method.