Reduced Toxicity and Aqueous-Based Solvent Using Phosphoric Acid as the Dopant Source for Formation Emitter Layer of Silicon Solar Cells

The challenges on Si solar cells are the usage of hazardous phosphorus oxychloride ( POCl3) for emitter formation and silane, and ammonia for the anti-reflective layer. This study focused on fabricating Si solar cells with less toxic material and an environmental-friendly process. The emitter junction was fabricated using a doctor blade (DB) with a less toxic phosphoric acid ( H3PO4) fabrication method. The emitter formation used an H3PO4 solution with various concentrations and diffusion temperatures. The temperatures varied from 850 degrees C to 925 degrees C. The obtained measured sheet resistances were in the range of 40 Omega/sq - 60 Omega/sq, which were suitable as an emitter junction and comparable to the existing methods. The prediction of junction depth was determined using a mathematical calculation based on the sheet resistance obtained from experiments. Thus, for the device fabrication, 10% of the H3PO4 solution was deposited using the DB method with a 30 min diffusion time. The H3PO4 thin film deposited by the DB method on the Si surface showed that different solution concentrations and diffusion temperatures affected the surface roughness and sheet resistance at fixed diffusion time. SiO2 was used as an alternative for the passivation layer to replace the toxic SiNx on the front surface. The thickness obtained was 140 nm. Therefore, the use of less toxic materials and low-temperature processing in the emitter and passivation may produce comparable values to industries.