Polar Species Modified Dielectric Constant of CsPbI₂Br Perovskite Nanocrystals: Implications for Carbon-Based Perovskite Solar Cells

Compared with organic–inorganic hybrid perovskite solar cells (PSCs), carbon-based all-inorganic PSCs have the advantages of low preparation cost, simple process, and good thermal stability. Here, three polar materials of 4-tert-Butylpyridine halides (tBPX: X = Cl, Br, I) are modified between the perovskite absorbent layer and the carbon electrode. On the one hand, the introduction of tBPX effectively improves the dielectric constant of perovskite nanocrystals and reduces the carrier trapping ability of defects. On the other hand, the structural–functional groups act on the perovskite interface, effectively passivate the surface defects of the perovskite nanoscale thick film, and reduce the nonradiative recombination loss of carriers. In addition, the interface modification of tBPX forms a hydrophobic protective barrier, which significantly improves the moisture resistance of the device. As a result, the carbon-based CsPbI2Br PSCs achieve a power conversion efficiency (PCE) of 14.39%, which is higher than 12.79% of the pristine device. The optimized device can maintain more than 80% of the original efficiency after 800 h of aging under a 20 ± 5% relative humidity in the atmospheric environment. Therefore, it provides an idea for the preparation of efficient and stable carbon-based all-inorganic PSCs.