Proceedings of MATSUS Spring 2025 Conference (MATSUSSpring25)
DOI: https://doi.org/10.29363/nanoge.matsusspring.2025.178
Publication date: 16th December 2024
Two-dimensional (2D) perovskites are of great scientific interest as they have exceptional optoelectronic properties and are easily tunable in their bandgap, making them viable to be used for a variety of optoelectronic devices, such as LEDs, solar cells and photodetectors. 2D perovskites have a multi-quantum well structure, with alternating layers of insulating organic spacer molecules and inorganic perovskite layers, with varying thickness given by the integer n. As a result, they have narrow excitonic features and large exciton binding energies of up to several hundred meV. This begs the question of how the excitonic dissociation in 2D perovskites works, as they show efficient charge carrier separation, despite the large excitonic binding energy.
For n>1 2D perovskites, so called edge states have been observed along the edges of single crystal flakes and the grain boundaries of thin films. The excitons dissociate into these edge states resulting in an efficient charge carrier separation. They show a red-shifted photoluminescence (PL), which dominates the PL signal in perovskite thin films. In n=1 2D perovskites, these states have not been observed. However, previously we demonstrated that even in n=1 2D perovskites efficient charge carrier separation takes place, enabling a 9 % external quantum efficiency in a photoconducting photodetector. [1]
In this work we provide insights into the process of charge carrier separation in n=1 2D perovskites using spatially resolved photocurrent measurements. We correlate photocurrent and PL, while exciting locally with a focused laser beam with a resolution of less than 1 µm. We observed higher photocurrents along the grain boundaries compared to the inside of the grains of butylammonium lead iodide (BA2PbI4). At the same time, the PL is less bright at the grain boundaries with the peak maximum being shifted slightly red and the peak being broader. This supports the hypothesis that edge states are existent within n=1 2D perovskites, even though they are not as easily observable in PL as in n>1 2D perovskites, and that they are crucial for the charge carrier separation. With our contribution we hope to shed light on the exciton dissociation in n=1 2D perovskites with the aim to improve device efficiency for those materials.
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