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Perfecting the current to build for the future: Silver Pastes for Current and New Generation Silicon Wafer Solar Cells

With the rapidly increasing solar PV installations in the country, it is expected that within the next several years, solar PV will become a significant contributor to India’s power requirements. Atmanirbhar Bharat Abhiyan is providing a significant push to developing raw materials and components within the country. In line with the Abhiyan, we have been working towards the development of PV grade silver paste used in the manufacturing of silicon solar cells. At the present solar cell production output, India imports around 50 tons/year of silver paste worth around INR 500 – 700 Crores per year.

Besides silver powder, the silver paste typically contains organic additives to make it screen printable and a customized glass powder in minor amounts which helps to etch the silicon nitride anti-reflection coating (ARC) during firing at elevated temperatures. The nature and amount of organic additives have to be highly customized to achieve a flow behaviour (rheology of paste) such that current collection grid lines of fine width can be printed on the ARC deposited silicon wafer. Etching the ARC layer, the glass powder also plays a crucial role in precipitating fine silver particles at the interface of the wafer and paste to develop the desired electrical contact.

Utilizing our experience in materials synthesis and designing of the flow behaviour of slurries and pastes, we initiated the work on the development of silver pastes. In the past 2-3 years, we have developed our silver powders, glass powder of suitable composition and formulated screen printable pastes. The NCPRE facilities were utilized to screen print as well as fire the wafers in both batch and continuous furnace to fabricate the solar cells. Till date, the best performing cells with our paste yielded 15% photo-conversion efficiency. Efforts are currently underway to establish the silver paste composition for the presently most popular industrial configuration of mono-crystalline p-type silicon wafers for Al-BSF and PERC architecture. Once pastes with superior repeatable performance are obtained, the knowledge would be applied to develop pastes for the emerging n-type silicon wafers solar cell technologies such as the HJT TOPCon followed by bifacial architectures also. We would be happy to receive any inputs from the industry towards the work being carried out on paste development and at a suitable time also seek their assistance in the evaluation of the pastes.

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Parag Bhargava
Dr. Ashok
Kumar Sharma