Advanced light trapping materials: Double layer ZnO:B based transparent conductive oxide

We present double layer structures consisting of ZnO:B/ZnO:B (BZO) and In2O3:Mo (IMO)/BZO films. The structure offers the unique opportunity of separating the conductivity of transparent conductive oxides from their light scattering behavior and allows their optimization for use in thin film solar cells. The layers serve as carrier transport and light trapping layers, respectively. BZO films were prepared by mid-frequency magnetic sputtering from a ZnO:B2O3 ceramic target. In order to enhance the conductivity of the BZO films, hydrogen was introduced into the sputtering atmosphere. Introducing hydrogen increased the mobility of the BZO-based double layer films to near 30 cm2/V
- s. Efficient scattering was achieved by etching the film in dilute hydrochloric acid. IMO films were also tested as the transport layer. An unconventional surface morphology was obtained by etching the IMO/BZO double layer film. Using this cascading multilayer structure IMO/BZO film as the front contact in a-Si:H solar cell, 20.4% and 7.4% enhancements in short circuit current density were obtained compared to smooth IMO films and textured single layer BZO films.