MOCVD ZnO/Screen Printed Ag Back Reflector for Flexible Thin Film Silicon Solar Cell Application

Amornrat Limmanee,Jaran Sritharathikhun,Sasiwimon Songtrai,Suttinan Jaroensathainchok,Taweewat Krajangsang,Kobsak Sriprapha,Patipan Krudtad

doi:10.1155/2014/939040

Abstract

We have prepared Ag back electrode by screen printing technique and developed MOCVD ZnO/screen printed Ag back reflector for flexible thin film silicon solar cell application. A discontinuity and poor contact interface between the MOCVD ZnO and screen printed Ag layers caused poor open circuit voltage (Voc) and low fill factor (FF); however, an insertion of a thin sputtered ZnO layer at the interface could solve this problem. The n type hydrogenated amorphous silicon (a-Si:H) film is preferable for the deposition on the surface of MOCVD ZnO film rather than the microcrystalline film due to its less sensitivity to textured surface, and this allowed an improvement in the FF. The n-i-p flexible amorphous silicon solar cell using the MOCVD ZnO/screen printed Ag back reflector showed an initial efficiency of 6.2% withVoc=0.86 V,Jsc=12.4 mA/cm2, and FF = 0.58 (1 cm2). The identical quantum efficiency and comparable performance to the cells using conventional sputtered Ag back electrode have verified the potential of the MOCVD ZnO/screen printed Ag back reflector and possible opportunity to use the screen printed Ag thick film for flexible thin film silicon solar cells.

Highlights

Researches regarding silicon solar cells prepared on flexible substrates such as polymer and stainless steel using n-i-p structure are of interest and have been intensively developed by many research groups [1,2,3,4,5,6]
The Ag paste used in this study is a commercial low temperature paste designed for solar cell applications. This Ag paste is normally employed to screen a front grid electrode of silicon wafer based and thin film solar cells, but we have examined new possibility to use it as a back electrode of flexible solar cell on polyimide (PI) substrate and to combine this printed layer with the metalorganic chemical vapor deposition (MOCVD) zinc oxide (ZnO) film to make an efficient back reflector
scanning electron microscopy (SEM) results reveal that the screen printed Ag layer is porous film composed of interconnected oval-shaped particles, as shown in Figure 1(a), which is totally different from Figure 1(b) which shows the sputtered Ag films with high density and smooth surface

Summary

Introduction

Researches regarding silicon solar cells prepared on flexible substrates such as polymer and stainless steel using n-i-p structure are of interest and have been intensively developed by many research groups [1,2,3,4,5,6]. Screen printing method of metal electrodes for microelectronic applications is used industrially in high volume production, allowing use of different types of substrates such as silicon wafer [9, 10] and polymer [11]. This technique has been applied to silicon wafer based solar cells for a long time [12, 13]; high temperature required for firing metal paste was not suitable for thin film solar cell process. Additional processes to improve interface between ZnO and Ag layers and optimization of n layer for depositing upon textured surface ZnO layer have been carried out

Experimental Details

Results and Discussions

Performance of Flexible Silicon Solar Cells Using Screen

Summary