Emitter saturation current densities of 22 fA/cm2applied to industrial PERC solar cells approaching 22% conversion efficiency

Passivated Emitter and Rear Cells (PERC) are currently being introduced into mass production. The conversion efficiency of industrialp‐type PERC cells is limited by the emitter saturation current density of around 90 fA/cm2of conventional homogeneously POCl3diffused emitters. In this paper we investigate two alternative emitter formation technologies. The first approach namedin‐situoxidation inserts a short thermal oxidation in‐between the phosphorus silicate glass deposition and the drive‐in of a conventional homogeneous POCl3diffusion thereby reducing the phosphorus surface concentration. The second approach named Gas Phase Etch Back (GEB) selectively removes around 40 nm of the highly doped surface of the POCl3diffused emitter by the reactive gas phase of the wet chemical rear polishing bath. Whereas the conventional POCl3emitter exhibits a phosphorus surface doping concentration of 3 × 1020 cm−3, thein‐situoxidation and the GEB process reduce the doping concentration to 7 × 1019 cm−3and 4 × 1019 cm−3, respectively. Accordingly, the emitter saturation current density is reduced to excellent values of 22 fA/cm2(in‐situoxidation) and 28 fA/cm2(GEB) compared with 89 fA/cm2for the reference POCl3diffusion. Whereas the reference POCl3emitter limits the PERC conversion efficiencyηto 21.1% and the open circuit voltageVocto 655 mV, thein‐situoxidation improves the PERC current–voltage parameters up to 21.3% and 663 mV. The highest efficiency of 21.6% is obtained with the selective GEB emitter. When solving series resistance issues with the most advanced GEB emitter, the measuredVocandJscvalues would support PERC conversion efficiencies up to 21.9%.