Nanostructure of Porous Si and Anodic SiO2 Surface Passivation for Improved Efficiency Porous Si Solar Cells.

Panus Sundarapura,Xiao-Mei Zhang,Alain Fave,Manabu Ihara,Ryoji Yogai,Kazuki Murakami

doi:10.3390/nano11020459

Abstract

The photovoltaic effect in the anodic formation of silicon dioxide (SiO2) on porous silicon (PS) surfaces was investigated toward developing a potential passivation technique to achieve high efficiency nanostructured Si solar cells. The PS layers were prepared by electrochemical anodization in hydrofluoric acid (HF) containing electrolyte. An anodic SiO2 layer was formed on the PS surface via a bottom-up anodization mechanism in HCl/H2O solution at room temperature. The thickness of the oxide layer for surface passivation was precisely controlled by adjusting the anodizing current density and the passivation time, for optimal oxidation on the PS layer while maintaining its original nanostructure. HRTEM characterization of the microstructure of the PS layer confirms an atomic lattice matching at the PS/Si interface. The dependence of photovoltaic performance, series resistance, and shunt resistance on passivation time was examined. Due to sufficient passivation on the PS surface, a sample with anodization duration of 30 s achieved the best conversion efficiency of 10.7%. The external quantum efficiency (EQE) and internal quantum efficiency (IQE) indicate a significant decrease in reflectivity due to the PS anti-reflection property and indicate superior performance due to SiO2 surface passivation. In conclusion, the surface of PS solar cells could be successfully passivated by electrochemical anodization.

Highlights

The initial increase in Jsc up to t of about 30 s indicates a suitable coverage of SiO 2 film on the surfaces of the pores resulting in the best ƞ. These results demonstrate that the bottom-up anodization process successfully fills tiny pores in the porous silicon (PS), and significantly decreases the Passivated PS-2-c cell
PS-1 and 176-nm-thick PS-2 layers confirmed a lattice matching at the PS/c-Si interface
The lowest reflectivity of approximately 9% was achieved for this thin PS-1 at a wavelength of 700–1100 nm, compared to 18% at 450–700 nm

Summary

Introduction

Si solar cells are dominating the photovoltaic (PV) market, in which state-of-the-art c-Si solar cells can achieve about 26.7% efficiency [2], approaching the Shockley–Queisser limit of 30% [3]

Methods

Results

Conclusion