CF4/O2 dry etching of textured crystalline silicon surface in a-Si:H/c-Si heterojunction for photovoltaic applications

We investigated a dry cleaning procedure of the crystalline substrate, both mono- and multi crystalline silicon, to leave an uncontaminated surface using an etching process involving CF4/O2 mixture. A detailed investigation was performed to find compatibility and optimisation of amorphous layer depositions both on flat and textured silicon by changing the plasma process parameters. We found evidence that plasma etching acts by removing the native oxide and the damages of textured silicon and by leaving an active layer on silicon surface suitable for the emitter deposition. SEM analysis confirmed that it is possible to find plasma process conditions where no appreciable damages and change in surface morphology are induced. By using this process we achieved on amorphous crystalline heterostructure a photovoltaic conversion efficiency of 13% on 51 cm2 and 14.5% on 1.26 cm2 active area. We also investigated compatibility of the process with industrial production of large area devices.