Ligand-Free, Highly Dispersed NiOx Nanocrystal for Efficient, Stable, Low-Temperature Processable Perovskite Solar Cells

Inverted configuration perovskite solar cells containing a NiOx 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 NiOx 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 NiOx layer (active area, 1.02cm(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 500h in a damp-heat test (85 degrees C and 85% relative humidity) due to there being less hydroxyl functional groups and H2O molecules on the NiOx surface, which degrade perovskite. Thus, we are able to successfully synthesize ligand-free NiOx for the low-temperature production of a high-performance, stable perovskite solar cell.