Resolving Hydrophobicity Issues of <i>tert</i>-Butyl Carbazole-Based Self-Assembled Monolayer through Interface Engineering Using Conjugated Polyelectrolytes for High-Performance Perovskite Solar Cells

As an interface engineering method for high-performance inverted perovskite solar cells (PSCs), self-assembled monolayers (SAMs) with hole-transport properties have been used to reduce energy losses at the hole-transport layer/perovskite interface. However, the application of <i>tert</i>-butyl carbazole-based SAMs has been limited by poor wettability of the perovskite precursor on the carbazole surface. To address this, a self-assembled bilayer (SAB) comprising a novel <i>tert</i>-butyl functionalized CBZC2 SAM and a conjugated polyelectrolyte wetting layer (PFN-Br) is proposed as the hole-transport layer (HTL) in CsI₀.₀₅FA₀.₉₂MA₀.₀₈Pb(I₀.₉₂Br₀.₀₈)₃ PSCs. The steric hindrance of the bulky <i>tert</i>-butyl group prevents aggregation and enhances hole extraction efficiency while reducing interfacial recombination losses. Notably, the <i>tert</i>-butyl carbazole SAB mitigates the stability issues of MeO-2PACz, leading to outstanding stability. CBZC2/PFN-Br-based PSCs achieved 24.1% efficiency, outperforming CBZC4/PFN-Br and MeO-2PACz. These devices showed a higher fill factor of 81.5%, compared to 73.8% for MeO-2PACz control based devices, and retained 96% of their initial efficiency after 500 h of maximum power point tracking. They also retained 90% and 85% efficiency after long-term stability test for 30 days at room temperature and under 85 °C heat exposure in nitrogen, respectively. These results highlight the potential of the <i>tert</i>-butyl carbazole SAM for the realization of high-performance PSCs.