Incorporation of a self-aligned selective emitter to realize highly efficient (12.8%) Si nanowire solar cells.

Formation of a selective emitter in crystalline silicon solar cells improves photovoltaic conversion efficiency by decoupling emitter regions for light absorption (moderately doped) and metallization (degenerately doped). However, use of a selective emitter in silicon nanowire (Si NW) solar cells is technologically challenging because of difficulties in forming robust Ohmic contacts that interface directly with the top-ends of nanowires. Here we describe a self-aligned selective emitter successfully integrated into an antireflective Si NW solar cell. By one-step metal-assisted chemical etching, NW arrays formed only at light-absorbing areas between top-metal grids while selectively retaining Ohmic contact regions underneath the metal grids. We observed a remarkable ∼40% enhancement in blue responses of internal quantum efficiency, corresponding to a conversion efficiency of 12.8% in comparison to the 8.05% of a conventional NW solar cell.