GAS PHASE ETCH BACK: A NEW SELECTIVE EMITTER TECHNOLOGY FOR HIGH-EFFICIENCY PERC SOLAR CELLS

摘要

We present a new selective emitter technology for industrial type passivated emitter and rear cells (PERC). Afterdouble sided texturing and POCl_3 diffusion (45 Ω/sq), we deposit an etch barrier by inkjet printing. We then polishthe textured rear surface by a single sided wet chemical polishing process removing about 8 μm of silicon at the rear.During the rear polishing, the reactive gas phase of the polishing bath etches about 50 nm of the front side emitter inbetween the etch barrier fingers. We name this novel selective emitter technology gas phase etch back (GEB). TheGEB emitter achieves saturation current densities J_(0e) of 67 fA/cm~2 at a sheet resistance of 88 Ω/sq compared to110 fA/cm~2 for a homogeneously POCl3-diffused emitter with 90 Ω/sq. Applying the GEB selective emitter to largeareaPERC solar cells with screen-printed metal contacts, we obtain up to 20.3% conversion efficiency, which is oneof the highest conversion efficiencies reported so far for industrial type PERC solar cells. The reference PERC cellwith homogeneously POCl_3-diffused emitter of 70 Ω/sq sheet resistance obtains 20.0% efficiency. The IQE analysisreveals a strongly improved blue response of the GEB selective emitter.