Towards 19% efficient industrial PERC devices using simultaneous front emitter and rear surface passivation by thermal oxidation

Higher solar cell efficiencies enable a reduction of the cost per watt ratio, if production effort is maintained at an acceptable level. A proven high-efficiency concept is the passivated emitter and rear cell (PERC). However, the transfer of this solar cell structure from demonstrator level to industrial application is challenging. We present a simple approach for the industrial fabrication of PERC solar cells which utilizes the simultaneous passivation of the front emitter and the rear surface by a thin layer of thermally grown oxide. This Thermal Oxide Passivated All Sides (TOPAS) structure represents an industrially feasible implementation of the PERC concept. Instead of using masking or sacrificial layers to obtain a structure with a textured, diffused front surface and a plain non-diffused rear surface, side selective wet chemical etching is chosen in this work, since it features a higher cost reduction potential. The current cell design features a selective emitter structure, introduced by laser-doping in combination with conventional screen-printed front contacts. With the presented approach we achieve an initial efficiency of 18.9 % on large area (149 cm²) 180 μm thick, Czochralski grown, boron doped p-type wafers. The stabilized device reaches a high open circuit voltage of V_oc = 641 mV. The comparison of the internal quantum efficiency of the TOPAS device and a full Al-back surface field (BSF) reference reveals a strong advantage in the blue and red response for the TOPAS concept.