The Ministry of New and Renewable Energy (MNRE) has established that only solar cells made from undiffused wafers will be eligible under the Domestic Content Requirement (DCR) policy, thereby banning the use of “blue” or diffused wafers.
This aims to guarantee that the key phases of solar cell production—such as diffusion, printing, and metallization—are conducted wholly in India to bolster the local solar sector. The production of solar cells starts with silicon ingots, created by melting and crystallizing high-quality silicon.
The ingots are subsequently cut into thin wafers employing precision slicing methods. These “black” or undiffused wafers serve as the foundational material for the manufacturing of solar cells. At this point, the wafers appear shiny, have a metallic sheen, or are somewhat gray and still lack the electrical characteristics necessary for photovoltaic performance.
They have to go through several steps to transform undiffused wafers into working solar cells. The initial essential phase is diffusion, during which wafers are placed in a controlled setting with elevated temperatures, enabling dopant elements such as phosphorus or boron to permeate the silicon surface. This procedure forms the crucial p-n junction, which is vital for transforming sunlight into electricity.
Avinash Hiranandani, Vice Chairman and Managing Director, RenewSys India, explained, “The process of making blue wafers begins with surface texturing using acid or alkaline solutions to create microscopic pyramid structures, along with thorough wafer cleaning to remove contaminants.
The wafers undergo doping or diffusion, where dopant elements like phosphorus or boron are introduced through thermal diffusion to modify their electrical properties. After diffusion, the wafers are annealed at high temperatures to activate and evenly distribute the dopants.”
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