Trap Density and Energy States in Organic-Inorganic Halide Perovskite Thin Films: A Study of Thickness Variations Using Drive Level Capacitance Profiling and Admittance Spectroscopy

Recently, organic-inorganic halide perovskite (OIHP) materials have gained significant prominence in various applications, especially in renewable energy and semiconductor technology, such as photovoltaic and thin film transistor (TFT) devices. Thickness of the OIHP film is an important factor in determining device characteristics. For example, an OHIP thin film thickness of approximately 30 nm must be achieved in order to achieve optimal on/off ratios and high mobility for TFT devices. Despite its critical importance, the relationship between halide perovskite film thickness and trap density has not been comprehensively explored. In this research, drive-level capacitance profiling (DLCP) and temperature derivative admittance spectroscopy (TAS) were used to investigate changes in trap energy and density depending on the thickness of the OHIP film. The DLCP and TAS methods were employed to explore the intricate relationship between OHIP film thickness and trap characteristics, providing insights into their effects on charge transfer dynamics and overall stability. From the DLCP and TAS analysis, it was observed that as the OHIP film thickness decreases, the trap density rapidly increases from 10¹⁵/cm³ to 10¹⁷/cm³ at the 0.35 eV trap energy level, due to the increasing influence of the interface caused by the reduction in OHIP film thickness. The defect energy level of 0.35 eV appears as an iodine interstitial defect, and we were able to improve device performances by applying an interface passivation process to remove iodine interstitial defects. We believe that this study provides a detailed analysis of the complex relationship between OHIP film thickness and trap states and can provide key research directions for OHIP-based photovoltaic and semiconductor devices and provide guidance for device optimization.