The Effects of Annealing Parameters on the Crystallization and Morphology of Cu(In,Ga)Se2Absorber Layers Prepared by Annealing Stacked Metallic Precursors

Chia-Ho Huang,Dong-Cherng Wen

doi:10.1155/2014/568648

Abstract

CIGS films are prepared by single-stage annealing of the solid Se-coated In/Cu-Ga bilayer precursor. The annealing processes were performed using various Ar pressures, heating rates, and soaking times. A higher Ar pressure is needed to fabricate highly crystalline CIGS films, as no extra Se-vapor source is supplied. As the heating rate increases, the surface morphologies of the CIGS films become looser and some cracks are observed. However, the influence of soaking time is insignificant and the selenization process only requires a short time when the precursors are selenized at a higher temperature with a lower heating rate and a higher Ar pressure. In this study, a dense chalcopyrite CIGS film with a thickness of about 1.5-1.6 μm, with large grains (~1.2 μm) and no cracking or peeling is obtained after selenizing at a temperature of 550°C, an Ar pressure of 300 Torr, a heating rate of 60°C/min, and a soaking time of 20 min. By adequate design of the stacked precursor and controlling the annealing parameters, single-stage annealing of the solid Se-coated In/Cu-Ga bilayer precursor is simplified for the fabrication of a fully crystallized chalcopyrite CIGS absorber layers with good crystallization and large grains.

Highlights

Chalcopyrite Cu(In,Ga)Se2 (CIGS) is a good absorber for high-efficiency thin film solar cells because of its favorable band gap and high-absorption coefficient for solar radiation [1]
A fully crystallized chalcopyrite CIGS absorber is fabricated by single-stage annealing of the solid Se-coated In/Cu-Ga
Increasing the heating rate is detrimental to the crystallinity of the CIGS films, because the amount of Se that can react with the metallic precursors depends on the time spent within the melting point range of In and Se

Summary

Introduction

Chalcopyrite Cu(In,Ga)Se2 (CIGS) is a good absorber for high-efficiency thin film solar cells because of its favorable band gap and high-absorption coefficient for solar radiation [1]. Of the various ways of preparing CIGS absorber, postselenization of precursor layers is one of the leading methods [2, 3], with an efficiency of around 20% for high temperature annealing of vacuum-sputtered metals under selenium vapor (i.e., selenization) [4, 5]. In spite of such an excellent device performance, a complete understanding of the material produced is required, because the properties of films depend greatly on the process parameters and affect the quality of the resulting CIGS films. The effect of annealing parameters, such as inert gas pressure, heating rate, and soaking time, on the structure and morphology of the CIGS absorber formed after selenization in an Ar containing atmosphere is determined in this paper

Experimental

Results and Discussion

Conclusions