TCO-free Low-temperature p+ Emitters for Back-junction c-Si Solar Cells

In this work, we report on the fabrication and characterization of n-type c-Si solar cells whose p+ emitters are based on laser processed aluminum oxide/silicon carbide (Al2O3/SiCx) films. The p+ emitter is defined at the rear side of the cell and it consists of point-like laser-diffused p+ regions with a surface charge induced emitter in between based on the high negative charge located at the Al2O3/c-Si interface. These emitters are fabricated at low temperature (< 400 °C) and could be directly compared to silicon heterojunction emitters with the advantage that the deposition of a Transparent Conductive Oxide (TCO) film can be avoided, since they are based on p+/n c-Si homojunctions. Additionally, the involved films are transparent to the IR photons ( >1000 nm) that reach the rear surface of the cell resulting in an excellent back reflector. We fabricated solar cells with distance between p+ regions or pitch ranging from 200 to 350 μm with a front surface based on silicon heterojunction technology. Best efficiency (18.1%) is obtained for a pitch of 250 μm as a consequence of the trade-off between Voc and FF values.