D-Camphorsulfonic Acid Modulated Self-Assembled Monolayer for Stable and Efficient Inverted Perovskite Solar Cells

In recent years, self-assembled molecular (SAM) hole-transport materials have boosted the efficiency of inverted perovskite solar cells. However, they also introduce numerous interfacial and structural challenges, presenting a double-edged sword for device development. Such as poor wettability for perovskite precursors-which adversely affects perovskite film quality-as well as insufficient stability and nonuniform formation. These issues cause localized inefficient charge transport and increased interfacial recombination, ultimately impairing device performance and reproducibility. To overcome these limitations, we introduced d-camphorsulfonic acid (D-CSA) as a multifunctional interfacial modifier. The strongly acidic sulfonic acid group (-SO₃H) of D-CSA plays a pivotal role: it enhances the wettability of the perovskite precursor on Me-4PACz ([4-(3,6-dimethyl-9<i>H</i>-carbazol-9-yl)butyl]phosphonic acid) and, acting as a proton donor, passivates the terminal carbazole group of Me-4PACz via protonation. Concurrently, the resulting sulfonate group (-SO₃^-) coordinates with undercoordinated Pb²⁺ ions from the perovskite layer. The incorporation of D-CSA also optimizes the energy level alignment between the HTL and the perovskite. The devices modified with D-CSA achieved a power conversion efficiency of 25.47% with negligible hysteresis, significantly outperforming the control devices (23.25%). Furthermore, the D-CSA-modified devices exhibited substantially enhanced moisture resistance, thermal stability, and operational stability under continuous illumination. This work provides a feasible strategy for developing highly efficient and stable inverted PSCs.