A new light trapping TCO for nc-Si:H solar cells

A new transparent conducting light trapping structure with no free carrier absorption for solar cells is described. Indium oxide doped with molybdenum (IMO), prepared by the hollow cathode sputtering technique, exhibits high charge-carrier mobility up to 80 cm²/V s. No free-carrier absorption in the near infrared region has been found in the IMO. The superior long-wavelength transparency, however, is not sufficient for thin film Si solar cell applications. To obtain the highest possible short circuit current, the TCO needs to possess additional light trapping structure. Anisotropic etching of fiber texture oriented ZnO has been shown to result in an effective light trapping structure. Here we propose a bilayer structure that consists of light trapping-intrinsic ZnO and IMO (the ZnO/IMO bilayer). Both layers show low free-carrier absorption up to the wavelength of 1200 nm. We demonstrate the use of such a transparent conducting light trapping oxide (TCLO) in nanocrystalline (nc-Si:H) solar cells fabricated by a single chamber, batch-type PECVD process. Incorporation of such a transparent conducting light trapping bilayer can increase solar cell short-circuit current density (J_sc) by >30% compared to flat bilayers.