Single-Stage Fabrication of Cu(In,Ga)Se2 Solar Cells by a Novel Route Based on Pulsed Electron Deposition

Cu(In,Ga)Se2 (CIGS) thin film solar cells are grown by the Pulsed Electron Deposition (PED) technique. Unlike other techniques, PED process allows the stoichiometric deposition of CIGS layers in a single stage, without requiring further treatments for selenization or Cu/(In+Ga) ratio adjustment. Due to the high kinetic energy of impinging adatoms on the substrate (1÷20 eV), dense CIGS films with [112]-oriented grains are obtained at low substrate temperatures (< 300°C), where Na diffusion from soda-lime glass is strongly inhibited, limiting the photovoltaic efficiency. Here, a novel method is proposed in order to supply the necessary Na content: a sodium fluoride (NaF) film is deposited by PED on Mo back contact, followed by a thermal annealing. Solar cells were completed using CdS deposited by Chemical Bath Deposition (CBD), a PED-deposited ZnO:Al (AZO) layer and evaporated Ni contact pads. No pure ZnO nor antireflection coating was applied.