Effect of TCO/μc-Si:H Interface Modification on Hydrogenated Microcrystalline Silicon Thin-Film Solar Cells

Shin-Wei Liang,Chuang-Chuang Tsai,Cheng-Hang Hsu

doi:10.1155/2013/756084

Abstract

The effects of H2plasma exposure on optical, electrical, and structural properties of fluorine-doped tin oxide (FTO) and AZO/FTO substrates have been investigated. With increasing the time of H2-plasma exposure, the hydrogen radical and ions penetrated through the FTO surface to form more suboxides such as SnO and metallic Sn, which was confirmed by the XPS analysis. The Sn reduction on the FTO surface can be effectively eliminated by capping the FTO with a very thin layer of sputtered aluminum-doped zinc oxide (AZO), as confirmed by the XPS analysis. By using the AZO/FTO as front TCO with the subsequent annealing, the p-i-nμc-Si:H cell exhibited a significantly enhancedJSCfrom 15.97 to 19.40 mA/cm2and an increased conversion efficiency from 5.69% to 7.09%. This significant enhancement was ascribed to the effective elimination of the Sn reduction on the FTO surface by the thin AZO layer during the Si-based thin-film deposition with hydrogen-rich plasma exposure. Moreover, the subsequent annealing of the sputtered AZO could lead to less defects as well as a better interface of AZO/FTO.

Highlights

Hydrogenated microcrystalline silicon is a promising material for high efficiency thin-film solar cells due to its advantages of reduced light-induced degradation and a lower bandgap, which lead to a higher photocurrent compared to hydrogenated amorphous silicon [1,2,3,4,5,6]
The aluminum-doped zinc oxide (AZO)/fluorine-doped tin oxide (FTO) after 72-second H2-plasma exposure showed comparable transmission compared to the FTO without H2plasma exposure, which should be due to the suppression of tin reduction by the thin AZO
This significant enhancement was ascribed to the effective elimination of the Sn reduction on the FTO surface by the thin AZO layer during the Si-based thin-film deposition with hydrogen-rich plasma exposure

Summary

Introduction

Hydrogenated microcrystalline silicon (μc-Si:H) is a promising material for high efficiency thin-film solar cells due to its advantages of reduced light-induced degradation and a lower bandgap, which lead to a higher photocurrent compared to hydrogenated amorphous silicon [1,2,3,4,5,6]. The superstrate p-i-n μc-Si:H solar cells are usually prepared by exposing the textured transparent conductive oxide (TCO) substrate to strongly hydrogen-diluted silane plasma. This can lead to the interactions of TCO with hydrogen plasma which results in chemical reduction of TCO surface. Schade et al reported that the optical transmission of tin oxide was reduced by the formation of an oxygen-depleted surface layer due to the chemical reduction of the oxide by the hydrogen plasma [7]. To eliminate or alleviate the chemical reduction of the TCO surface, other group has replaced indium tin oxide (ITO) or fluorine-doped tin oxide (FTO) with a layer of textured aluminum-doped zinc oxide (AZO), which is more resistant to plasma damage [13, 14]. We introduced a very thin AZO coating (3–5 nm) onto the textured FTO glass to maintain the light trapping and preserve the quality of the TCO/μc-Si:H interface for μc-Si:H single-junction solar cells

Experimental Details

Results and Discussion

Conclusion