40 Years of Inversion Layer Solar Cells: From MOS to Conducting Polymer/Inorganic Hybrids

In recent years, conducting and semiconducting polymers such as PEDOT:PSS and P3HT have become commercially available, and as a result, a new type of polymer/Si heterostructure solar cell is emerging. With a conducting polymer (a degenerate semiconductor) as emitter, such an organic/inorganic hybrid heterojunction is likely to achieve high conversion efficiencies only if the inorganic semiconductor is pushed into strong inversion to reduce dramatically the space-charge recombination and to mitigate the poor lateral conductance of the polymeric layer. We explain this notion through a review of the types of solar cells based on an inversion layer, induced in the semiconductor absorber by a metal, by a dielectric material with fixed charges, or by another semiconductor. In these types, which include the metal-insulator-semiconductor (MIS), semiconductor-insulator-semiconductor, and MIS inversion layer solar cells, interfaces play a crucial role, even more so than in other forms of solid-state photovoltaics. We also point out the strategy by which atomic-layer-deposited Al₂O₃ can be used to form an inversion layer solar cell on an n-Si emitter.