Solution-based n-type doping in metal oxides for next-generation solar cells

Solution-based doping methods are particularly suitable for low-cost, high-throughput and large-area processing of next-generation solar cells. In this paper, we review our recent progress in n-type doping of metal oxides during electrochemical deposition of these materials, including ZnO and Cu ₂O. For naturally n-type ZnO, n-type doping is achieved by substituting the cation (Zn) with a group III element (Al or Ga). In naturally p-type Cu₂O, n-type doping is realized by substituting the anion (O) with a halogen (Cl or Br). The latter is of particular interest since it is in principle a universal n-type doping technique for all chalcogenides, while cation substitution has to be worked out on a case-by-case basis depending on the cation valence. In both cases, the doping mechanism is believed to be co-precipitation of either ZnO with dopant oxide (Al₂O₃ or Ga₂O₃) or Cu₂O with Cu halide (CuCl or CuBr). Several 3rd-generation concepts are enabled by these solution-based doping methods, including 1) a radial p-n junction in chalcogenide nanowires for enhanced charge separation at the organic/inorganic interface and 2) a 3-dimentional p-n junction through chalcogenide nanowires as a new cell architecture for next-generation inorganic solar cells.