Erfurt, D.; Heinemann, M. D.; Schmidt, S.S.; Körner, S.; Szyszka, B.; Klenk, R.; Schlatmann, R.: Influence of ZnO-Based Sub-Layers on the Growth of Hydrogen Doped Indium Oxide. ACS Applied Energy Materials 1 (2018), p. 5490-5499
10.1021/acsaem.8b01039
Open Accesn Version

Abstract:
Because of its high mobility, hydrogen-doped indium oxide (In2O3:H) has a high potential as front contact in thin film or Si heterojunction solar cells. Certain growth conditions are required to process high-mobility In2O3:H. In Cu(In,Ga)Se2 (CIGS) devices, the growth of In2O3:H is influenced by the existing sublayers. Therefore, the intention of the present study is to investigate these influences on In2O3:H, deposited by pulsed direct current magnetron sputtering onto bare glass substrates or Zn(O,S) and ZnO layers, as they are commonly used in CIGS solar cells. The amorphous Zn(O,S) and the crystalline ZnO films were deposited by radio frequency sputtering onto planar glass as well as rough CIGS samples. On the basis of X-ray diffraction and transmission electron microscopy measurements, the structure of the as-grown In2O3:H films was evaluated. X-ray diffraction patterns show amorphous growth on glass and Zn(O,S) and a higher crystallinity of In2O3:H films grown on ZnO layers. The preferred orientation of In2O3:H films changes from (222) to (400) when grown on ZnO layers with small grains. A pronounced crystalline growth leads to a reduction in charge carrier density and electron mobility. This was found for crystalline grown In2O3:H on planar glass as well as on rough CIGS samples in combination with a ZnO layer. A post deposition thermal treatment leads to the crystallization of amorphous phases and reduces strain in crystalline grown films, increasing the electron mobility for all films. However, the electrical properties of the crystalline-grown In2O3:H films did not improve sufficiently.