Self-Assembled Discotic Liquid Crystals as Stability Enhancing Hole Transport Layers for Ruddlesden–Popper Perovskite Optoelectronics

Metal halide perovskites have emerged as highly efficient materials for next-generation optoelectronic devices; however, their instability under humid and thermal conditions remains a fundamental challenge. In this work, we examine the degradation behavior of the prototypical methylammonium lead iodide (MAPbI₃) perovskite and its stabilization through surface modification and dimensional control. The structural and optical properties of perovskites coated with the conventional spiro-OMeTAD and the discotic liquid crystal 2,3,6,7,10,11-hexakis(pentyloxy)triphenylene (HAT5) are systematically compared. Butylammonium iodide (BAI) is incorporated to form mixed-dimensional Ruddlesden–Popper phases, and the films are subjected to 45 days of aging under ambient humidity (36–58%) and repeated heating at 65 °C in air. Our results demonstrate that the HAT5 coating effectively slows the conversion of MAPbI₃ into PbI₂ and retains the optical and structural properties of the perovskite, indicating the improved environmental stability compared to spiro-OMeTAD. The enhanced stability is attributed to the hydrophobic character and ordered columnar packing of the DLC, which acts as a protective interface. While the low phase-transition temperature of HAT5 may limit its operational range, these findings demonstrate that discotic liquid crystals represent a promising class of molecularly engineered hole-transport materials for improving the durability of perovskite-based optoelectronic devices.