Towards realization of a δ-BSF solar cell

Our previous modeling and simulation demonstrated that a considerable increase in Si single-crystal BSF solar cell performance is possible by emitter modifications to give a δ-BSF device. The idea that the emitter with an inserted layer (complex interface) is able to significantly widen the optical absorption is now proven. To be efficient, optical and electronic improvements have to act simultaneously. An experimental efficiency study of the δ-BSF solar cell can be made only on a completely built device because of interactions on the material and device levels. In our first approach we have obtained results on simplified devices, where in the case of the most developed structure, only emitter with inserted sub-structure, the base, the BSF and contacts were present. Measurements of optical absorption and carrier photogeneration were carried out on the same samples but at different technological stages. Improvements in the fundamental features, as widened absorption and infrared photoconductivity have been obtained. In both cases the presented results are very encouraging. The improvement in the absorption is the best yet observed (up to λ⩽3200 nm). The infrared photocurrent was first observed in a single-crystal Si device (the upper wavelength limit was imposed by the emitting lamp, λ⩽1900 nm). These results have been completed with transmission and reflection measurements and by the efficiency characterization of the simplified Si single-junction device in nonconcentrated light