Ligand‐Free, Highly Dispersed NiO x Nanocrystal for Efficient, Stable, Low‐Temperature Processable Perovskite Solar Cells

Inverted configuration perovskite solar cells containing a NiO x layer fabricated by using a low‐temperature process have yielded highly efficient, flexible devices. However, the instability of these devices has limited their commercial application. Here, we report high‐quality, ligand‐free NiO x nanocrystals, prepared directly through a facile organic solvent method, that form a stable ink when dispersed in an ethanol solvent. Rigid and flexible devices containing a NiO x layer (active area, 1.02 cm 2 ) fabricated with this ink at low‐temperature achieved efficiencies of 18.49 and 15.89%, respectively. In addition, the devices retain 90% of their initial performance at 500 h in a damp‐heat test (85 °C and 85% relative humidity) due to there being less hydroxyl functional groups and H 2 O molecules on the NiO x surface, which degrade perovskite. Thus, we are able to successfully synthesize ligand‐free NiO x for the low‐temperature production of a high‐performance, stable perovskite solar cell.