Understanding the Heterointerfaces in Perovskite Solar Cells via Hole Selective Layer Surface Functionalization

Interfaces in perovskite solar cells (PSCs) play a pivotal role in determining device performance by influencing charge transport and recombination. Understanding the physical processes at these interfaces is essential for achieving high-power conversion efficiency in PSCs. Particularly, the interfaces involving oxide-based transport layers are susceptible to defects like dangling bonds, excess oxygen, or oxygen deficiency. To address this issue, the surface of NiO_x is passivated using octadecylphosphonic acid (ODPA), resulting in improved charge transport across the perovskite hole transport layer (HTL) interface. This surface treatment has led to the development of hysteresis-free devices with an impressive ≈13% increase in power conversion efficiency. Computational studies have explored the halide perovskite architecture of ODPA-treated HTL/Perovskite, aiming to unlock superior photovoltaic performance. The ODPA surface functionalization has demonstrated enhanced device performance, characterized by superior charge exchange capacity. Moreover, higher band-to-band recombination in photoluminescence and electroluminescence indicates presence of lower mid-gap energy states, thereby increasing the effective photogenerated carrier density. These findings are expected to promote the utilization of various phosphonic acid-based self-assembly monolayers for surface passivation of oxide-based transport layers in perovskite solar cells. Ultimately, this research contributes to the realization of efficient halide PSCs by harnessing the favorable architecture of NiO_x interfaces.