In situ laser generation of NiO 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 ([email protected]X) as the electrode for HTL-free C–PSCs. Due to the desired morphology of the LIG flakes, it enables the formation of a compact [email protected]X 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 [email protected]X 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. This is due to a remarkable improvement in the physical contact at the carbon/perovskite interface using [email protected]X. Moreover, the PSCs based on [email protected]X 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.