Polyimide for Silicon Solar Cells with Double-Sided Textured Pyramids

Silicon solar cells incorporating double-sided pyramidal texture are capable of superior light trapping over cells with front-side only texture. However, increased surface area, roughness and exposed <111> crystal planes of textured surfaces not only causes increased recombination, but also makes cells susceptible to shunting through pinholes in the dielectric at the sharp peaks and valleys of the textured pyramids. A polyimide film as an insulating interlayer film is investigated to circumvent the tradeoff between improved light trapping, increased recombination and increased shunt paths. When applied at the rear of the interdigitated back contact silicon solar cell structure, the polyimide film provides an excellent electrical insulation (>1000 MΩ of insulation resistance) and increases photocurrent (~1.1 mA/cm) owing to an increased rear internal reflectance. The polyimide is also compatible with metal annealing of passivating dielectrics such as silicon nitride. Optical simulation and experimental results are combined in a 3D semiconductor simulation (Quokka) to quantify the possible gain of implementing the double-sided texture in high efficiency silicon solar cells. Index Terms — rear texture, diffusions, passivation, PECVD nitride, ALD AlOx, back-contact, ray trace, solar cell, high efficiency, polyimide, photoluminescence spectroscopy, band to band absorption, IBC.