In situ laser generation of NiOX nanoparticles embedded in graphene flakes for ambient-processed hole-transport-layer-free perovskite solar cells

Carbon-based hole-transport-layer-free perovskite solar cells (HTL-free C-PSCs) have gained tremendous attention due to their low cost, ease of fabrication, low-temperature processability, and excellent long-term stability. However, HTL-free C-PSCs suffer from poor interfacial contact at the carbon/perovskite and limited hole extraction ability, thereby limiting the device's performance. Herein, an in situ one-step synthesis strategy is presented to simultaneously generate laser-induced graphene flakes (LIG) embedded with the uniformly distributed fine NiOX nanoparticles (LIG@NiOX) as the electrode for HTL-free C-PSCs. Due to the desired morphology of the LIG flakes, it enables the formation of a compact LIG@NiOX electrode without a post-heat treatment or hot-pressing process. As a result, the fully ambient-processed HTL-free C-PSCs prepared under a high relative humidity of around 50-70% based on the LIG@NiOX achieve a power conversion efficiency (PCE) of up to 14.46%, compared to a PCE of 10.36% for the PSCs based on the commercial graphite/carbon black. This is due to a remarkable improvement in the physical contact at the carbon/perovskite interface using LIG@NiOX. Moreover, the PSCs based on LIG@NiOX retained 94% of their initial PCEs after 185 days of storage in ambient air, compared to those based on the Spiro-OMeTAD/Au that only retained 78% of their initial PCEs after 84 days of storage under the same ambient condition. The laser process opens a new avenue for simultaneous forming LIG embedded with the in situ formed metal oxide nanoparticles for various applications.