Black silicon (BS) using room temperature reactive ion etching (RT- RIE) for interdigitated back contact (IBC) silicon solar cells

Black silicon processing is a promising research area to improve optical properties of silicon solar cells. Currently, RIE method is used at cryogenic temperature because it enables a very good control of shapes of nano-structures but working at cryogenic temperature in a clean room can be an issue. In order to produce black silicon under realistic industrial conditions, room temperature process has to be achieved. We present a study aiming at etching silicon wafer surfaces using "Room Temperature SF6/O-2 Reactive Ion Etching" (RT-RIE). The BS obtained using RT-RIE results in a morphology consisting of 850 nm height pillars densely and randomly distributed onto the silicon surface. We show that the shape, density and height of nano-structures are modified by small variations of the parameter process due to the sensitive competition between etching and passivation mechanisms. The BS exhibits a reflectance below 1% in the whole visible wavelength range. The next step is the integration of this BS into interdigitated back contacts (IBC) solar cells. We then model IBC solar cells using the Silvaco software. The surface recombination velocity is strongly enhanced with BS and charges cannot be collected at the back of the cell. The charges generated by photon absorption within the first micrometers of the cells are recombined before being collected at the back contact. A front passivation is then necessary to reduce this strong surface recombination velocity. As a result, simulation exhibits efficiency variations from 1% without passivation to 23% with high quality passivation.