Development of an emitter for industrial silicon solar cells using the doped oxide solid source diffusion technique

The aim of this paper is to demonstrate for the first time the feasibility of fabricating large-area screen-printed monocrystalline silicon solar cells using the Doped Oxide Solid Source (DOSS) diffusion technique. This process was applied to form the n⁺p emitter junction from highly doped sources prepared in a POCl₃ ambient. The diffusions were performed under a pure nitrogen flow in the temperature range 900–1050°C. In this investigation attention was devoted to the influence of the source doping level on the fill factor. The solar cells were fabricated on industrial quality 4-inch Cz wafers using a simple processing sequence incorporating screen-printed contacts and a TiO₂ antireflection coating deposited by spin-on. Fill factors as high as 79% were obtained. The potential benefit of retaining for passivation purposes the thin residual oxide grown during phosphorus diffusion was evaluated. These first experiments led to a cell efficiency close to 10%.