Growth and Properties of ZnO:Al on Textured Glass for Thin Film Solar Cells

Marta Lluscà,Joan Bertomeu,Aldrin Antony

doi:10.1155/2014/406495

Abstract

Aluminium induced texturing (AIT) method has been used to texture glass substrates in order to enhance the photon absorption in thin film solar cells. The resultant glass roughness has been analyzed by varying the AIT process parameters and it has been found that the deposition method of Al is a decisive factor in tuning the texture. Two types of textures, a soft (texture E) and a rough texture (texture S), were achieved from the thermally evaporated and sputtered Al layers through AIT process. Aluminium-doped zinc oxide (AZO) layers of different thickness were deposited over both textures and over smooth glass. Haze values above 30% were obtained for texture S + AZO and above 10% for texture E + AZO. The resultant morphologies were free from sharp edges or deep valleys and the transparency and the resistivity values were also good enough to be used as front contact for thin film solar cells. In order to demonstrate the light absorption enhancement in a solar cell device, 200 nm of a-Si:H followed by 300 nm of Ag were grown over the textured and smooth substrates with AZO, and an optical absorption enhancement of 35% for texture E and 53% for texture S was obtained in comparison to the smooth substrate.

Highlights

Use of textured and conducting front contacts in thin film silicon solar cells enhance photon absorption in active layers
Texturing of glass substrate is an interesting alternative to enhance light trapping instead of using conventional naturally textured transparent conducting oxides such as ZnO:B grown by LPCVD [2], SnO2:F grown by APCVD [3], or through HCl etching of sputtered ZnO:Al (AZO) [4]
In this work different types of textures have been achieved by varying the aluminium induced texturing (AIT) process parameters such as Al thickness, annealing time, and etching temperature, but a special attention has been given to the Al deposition method that

Summary

Introduction

Use of textured and conducting front contacts in thin film silicon solar cells enhance photon absorption in active layers. The texturing of the glass substrate by aluminium induced texturing (AIT) as an alternative to improve optical behaviour of thin film solar cells is studied as well as the growth of sputtered AZO over these textured glass surfaces. The high temperature during the thermal annealing of the Al coated glass favours a spatially non-uniform redox reaction according to the following equation: 4Al + 3SiO2 󳨀→ 2Al2O3 + 3Si (1) Followed by this thermal annealing, the reaction products (Al2O3 and Si) are removed by a wet chemical etching and the result is a rough and uniform texture over the glass surface. In this work different types of textures have been achieved by varying the AIT process parameters such as Al thickness, annealing time, and etching temperature, but a special attention has been given to the Al deposition method that.

Experimental

Results and Discussion

Conflict of Interests

Conclusion