A Novel Approach for Mask-Free Selective Emitter Technology Combining Laser Doping and Wet Chemical Etch Back

In this paper a novel process for a mask-free technology to manufacture selective emitter structures is presented. A solid state laser system was used for dry laser over-doping after POCl3 diffusion forming the selective emitter structure. Further emitter enhancement of the intermediate areas has been achieved by a controlled emitter etch back within a wet chemical etching process. We investigated the etching rate and the surface quality through the sheet resistance of the emitter, respectively. Two different emitters were used in the solar cell process and compared. Emitter saturation current density J0e data of lowly doped and laser doped etch back emitters are shown. Emitter saturation currents in the etched back areas down to J0e = 138 fA/cm2 have been achieved leading to maximum open circuit voltages around 670 mV. By optimizing the laser parameters, an etching within the laser doped areas can be suppressed, hence during emitter etch back no masking of the intended later contact areas is necessary.