Interfacial engineering with a monobromo-carbazole-based molecular modifier for a robust PTAA/perovskite heterointerface

• A monobromo-carbazole-based molecular modifier (3Br-Cz-4PA) strengthens the PTAA/perovskite heterointerface. • 3Br-Cz-4PA effectively passivates undercoordinated Pb defects at the buried interface. • 3Br-Cz-4PA modification facilitates hole extraction due to a kinetically favorable energy level alignment. • 3Br-Cz-4PA interface engineering enhances the PCE and improved shelf stability under ambient conditions. The fine-tuning of the interfacial properties between the hole transport layer (HTL) and the active perovskite layer is important to achieve high efficiency in inverted perovskite solar cells (PSCs). Interfacial layers are crucial in aligning energy levels and mitigating defect-induced losses, thereby facilitating charge transfer and device stability. This study introduces an advanced interfacial engineering technique via utilization of an asymmetric monobromo-substituted carbazole-based molecular modifier, [4-(3-bromo-9H-carbazol-9-yl)butyl]phosphonic acid (3Br-Cz-4PA), to improve the compatibility between the underlying HTL of poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) and the perovskite layer of methylammonium lead iodide (MAPbI 3 ). Through the integrated density functional theory calculations and empirical studies, it is revealed that 3Br-Cz-4PA not only passivates undercoordinated Pb defects but also facilitates hole extraction by suppressing non-radiative recombination. Moreover, this approach yields a notable improvement in the grain growth and crystallinity of perovskite films. Consequently, PSCs enhanced with 3Br-Cz-4PA demonstrate a remarkable power conversion efficiency of 19.3 %, minimal hysteresis, and superior shelf-life stability, positioning this methodology as a substantial leap forward photovoltaic technology.