Efficiency improvement of crystalline silicon solar cells

To increase the efficiency and reduce the production cost of crystalline silicon (c-Si) solar cells, efforts in the photovoltaic industry are currently put on the process optimization of the cell. Sodium hydroxide/Potassium hydroxide (NaOH/KOH) and isopropyl alcohol (IPA) are widely used in the standard alkaline texturization of mono crystalline silicon (mc-Si) wafers for enhancing the optical efficiency, where IPA promotes the formation of pyramidal structure but unfortunately leads to unstable process. In this work, carbohydrates are investigated as an additive in the etchant solution; its capability to replace IPA as texturing solution is discussed. A pre-texture cleaning agent is introduced to remove the organic residue from the textured surface. Moreover, uniform phosphorus diffusion process for B2B (back to back) diffusion is investigated with single and multiple temperature plateaus. Impact of a pre-oxygen step on the phosphorus diffusion is investigated where number of inactive phosphorus at the PSG (phosphosilicate glass)-Si interface is reduced. Anti reflection coating (ARC) of the silicon nitride (SiNx) dielectric layer and sintering process are also optimized to improve the passivation and reduction of series resistance (Rs). A batch of 156mm pseudo square (PSQ) mc-Si cells was fabricated using the above mentioned suggestions. The estimated average efficiencies is 18%-18.25%, compared to the standard process it is higher by ~0.75-1.0 %. For the improved process, surface morphology, reflectance factor (RF), sheet resistance(SR) uniformity, carrier effective life time (τeff), open circuit voltage (Voc), short circuit current (Isc), fill factor (FF), shunt resistance (Rsh), peak power (Ppk) and efficiency(η) are given and compared with the standard process of solar cells.