Silicon and Germanium Nanocrystal Inks for Low-Cost Solar Cells

Silicon is the most widely used material in the microelectronics and photovoltaics industry. Currently it is used in one of two forms: as wafers of single- or polycrystalline material or as CVD deposited thin film material. While crystalline silicon solar cells achieve high efficiencies, the silicon wafer contributes significantly to the module cost. Thin film silicon solar cells can be produced at much lower cost, but they also feature lower efficiencies. In this presentation, we discuss an alternate route to forming silicon (Si) or germanium (Ge) thin films from solution on flexible substrates. Silicon (germanium) nanocrystals are formed in a nonthermal plasma. In the plasma environment a Si/Ge precursor is broken down by electron impact, leading to the nucleation and growth of Si or Ge crystals. By adding dopant precursors, p- and n-doped as well as intrinsic crystals can be formed. Organic ligands can be attached in the plasma such that nanocrystals become soluble in organic solvents. These “nanocrystal inks” can be used to form Si or Ge films with ultra-low-cost printing or coating techniques. Film properties of Si/Ge-ink processed films will be discussed. Proof-of-concept demonstrations of solar cells produced from silicon inks will be presented.