Hole transportation and defect passivation properties at the perovskite/SAHTM interface: the effect of heteroatom groups and alkyl chain lengths in self-assembled phosphonic acid carbazole derivatives

Self-assembled hole transporting materials (SAHTMs) are essential for enhancing the performance of perovskite solar cells (PSCs). However, the improvement of both the hole transportation and the defect passivation abilities of SAHTMs is challenging. In this work, modifications of various heteroatom groups and alkyl chain lengths were introduced in six phosphonic acid carbazole (PACz) SAHTMs for the purpose of elevating their hole mobility and the properties of the perovskite/SAHTM interface. Density functional theory was employed for the investigations on the photoelectric properties of phosphonic acid carbazole derivatives, including ground and excited state geometries, crystal stacking mode, charge transfer properties, stability, solubility, polarity, absorption and fluorescence emission, and so on. Furthermore, the perovskite/SAHTM interface properties, such as the interaction between adjacent atoms, adsorption and defect passivation, were fully understood. The calculated results reveal that the PACz materials exhibit hole and electron mobilities of up to 4.21 and 17.99 cm² V^–1 s^–1, respectively. An improved hole extraction capacity was observed due to the favorable energy alignment between the PACz derivatives and the perovskite materials. Strong interactions of the studied molecules with the perovskite surface were identified through SAHTM-Pb²⁺ attractions and the SAHTM/perovskite interface characteristics. Consequently, enhanced hole transportation and reduced defects at the perovskite/ SAHTM interface are anticipated, which is crucial for advancing high-performance PSCs.