Simultaneous front emitter and rear surface passivation by thermal oxidation - an industrially feasible approach to a 19% efficient PERC device

In this work, we present a simple approach for the transfer of the passivated emitter and rear cell (PERC) device structure from laboratory status to industrial manufacturing. The approach uses a thin layer of thermally grown oxide for the simultaneous passivation of both front emitter and rear surface. This Thermal Oxide Passivated All Sides (TOPAS) structure represents an industrially feasible design of the PERC concept, as we circumvent costly masking steps. Instead side selective, wet-chemical etching allows the realisation of a structure with a textured and diffused front surface and a plain, non diffused rear surface. The implementation of a selective emitter by laser-doping from a phosphosilicate glass source enables the use of screen-printed Ag front contacts. With the presented approach, on 180 µm thick boron-doped Czochralski (Cz) grown silicon wafers of base resistivity 1.6 ohm cm we achieve efficiencies of up to 18.9 % (initial) and a high open-circuit voltage of 641 mV (stable). The antireflection coating stack of a thin thermal oxide and a SiNX layer on top yields a lower emitter dark saturation current density than a single SiNX layer. Furthermore, we present similar values for the specific cost of the standard Al-BSF solar cell process and the presented TOPAS process.