Controlling Band-Bending for Perovskite Optoelectronic Devices Using Bismuth-Based Interlayers

Interface engineering is a powerful tool for enhancing electron/hole transfer and extraction, as well as reducing charge carrier recombination in perovskite-based optoelectronic devices, including light-emitting diodes (LEDs) and photovoltaic (PV) devices. Here, incorporating an interlayer between the perovskite and charge transport layers has been an extremely successful approach to fine-tune energy level alignment, boosting device performance. In this work, we investigate the incorporation of bismuth-based perovskitoids as interlayers to deepen the position of the perovskite's conduction band. Our results clearly show that perovskite solar cells based on a PIN architecture with a triple-cation composition (TC) incorporating the bismuth-based interlayer outperform those without when using C₆₀-fullerene (C₆₀) as the electron charge extraction layer. We attribute this improvement to the deepening of the conduction band position by approximately 0.5 eV, which agrees with the X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) measurements. These findings demonstrate the potential of Bi-based perovskitoid as interlayers to induce band bending in the perovskite layer, effectively allowing fine-tuning of the energy level alignment at the device interfaces, thereby paving the way for future optoelectronic technologies.