Optimization of sputtering NiOx films for perovskite solar cell applications

In this work, we systematically investigated the properties of three kinds of NiOx films prepared by magnetron sputtering either NiO or Ni target under direct current (DC) or radio frequency (RF) power without any preheating. Those NiOx films were found to be different in composition ratios, lattice strain and energy levels, thus showing different optical and carrier transport properties. By RF power source, sputtering Ni target in pure O-2 atmosphere led to NiOx film with relatively good crystallization and surface properties compared with other two types of NiOx films. These NiOx films were further introduced into CH3NH3PbI3 based planar p-i-n heterojunction perovskite solar cells (PSCs) as the hole transport layers (HTL). It is revealed that PSCs based on NiOx HTL prepared by sputtering Ni target in pure O-2 atmosphere achieved a highest power conversion efficiency of 16.3% with negligible hysteresis. Compared with devices with PEDOT:PSS HTL, PSCs based on magnetron sputtered NiOx HTL presented substantially improved stability in air. The results provide theoretical and experimental guidance on selecting NiOx HTLs fabricated by magnetron sputtering techniques.