CIGS Solar Cell Fabrication and Firing Parameters on Efficiency of Thin-Film CIGS Solar Cells


Introduction

The growing demand for renewable energy solutions has led to the exploration of innovative photovoltaic technologies. Among these, thin-film photovoltaics, including Copper Indium Gallium Selenide (CIGS) solar cells, have emerged as promising alternatives to traditional silicon-based solar cells. CIGS solar cells offer high efficiency and flexibility, making them an attractive option for sustainable energy generation. This article investigates the impact of belt furnace and firing parameters on the efficiency of thin-film CIGS solar cells, shedding light on the manufacturing process and the critical factors influencing cell performance.

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CIGS Solar Cell Fabrication

CIGS solar cells are composed of layers of semiconductor materials that effectively convert sunlight into electricity. The fabrication process involves depositing copper, indium, gallium, and selenium onto a substrate material through a sputtering process. This is followed by controlled annealing at elevated temperatures to create a functional solar cell structure. The key layers include the molybdenum back contact, CIGS absorber layer, cadmium sulfide (CDS) buffer layer, and the front contact layer made of zinc oxide (ZnO).

Processing in a Belt Furnace

The belt furnace plays a crucial role in the manufacturing of CIGS solar cells. The furnace is designed to accommodate high temperatures and controlled atmospheres necessary for the selenization process. During this process, the deposited materials undergo annealing and selenization, where they are exposed to hydrogen sulfide gas to promote sulfurization. The temperature and soaking times during selenization significantly impact the efficiency of the resulting solar cell.

Effect of Selenization Profile on Efficiency

"Selenization and sulfurization (SAS) refer to the transformative processes where a material's surface interacts with a high-temperature atmosphere containing selenium and/or sulfur. During these reactions, the surface undergoes a chemical change, giving rise to a novel compound that incorporates either selenium or sulfur, or even a hybrid blend of both elements."

Researchers have extensively studied the influence of selenization parameters on CIGS solar cell efficiency. The sintering temperature and soaking times have been identified as critical factors affecting grain growth and cell performance. Optimal conditions involve sintering temperatures above 500 C and soaking periods between 30 and 60 minutes. The selenization profile determines the quality and characteristics of the CIGS thin film, influencing its efficiency and overall performance.

Selenization profile of CIGS solar cell, THT book
Selenization profile of CIGS solar cell, THT book

Belt Furnace Design for CIGS Processing

To achieve efficient CIGS solar cell fabrication, a well-designed belt furnace is essential. The furnace must be capable of operating at temperatures exceeding 650 C, with excellent cross-belt uniformity to accommodate larger substrates. A muffle is incorporated to maintain a clean processing environment, as various gases are introduced during different phases of CIGS processing. Torrey Hills Technologies has developed a furnace suitable for thin-film solar applications, featuring ceramic heater boards, precise temperature control, and the capacity to accommodate wider substrates.

Conclusion

Thin-film CIGS solar cells hold significant promise as a renewable energy solution, with high efficiency and flexibility making them stand out in the field of photovoltaic technologies. The belt furnace and firing parameters during the selenization process play a crucial role in determining the efficiency and performance of CIGS solar cells. Optimal conditions involve elevated temperatures, appropriate soaking times, and careful control of the selenization profile. As advancements in furnace technology and processing parameters continue, the potential for highly efficient and cost-effective CIGS solar cells becomes increasingly attainable, contributing to a sustainable energy future.

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