Enhanced Photodetection Performance of In Situ Core/Shell Perovskite-MoS₂ Heterostructure Phototransistor

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) are promising materials for various optoelectronic device applications due to their tunable band gap, simple fabrication, interesting excitonic properties, and chiral light-matter interaction from the spin-valley locking [1]. However, their atomic-level thinness results in low light absorption, which hinders the sensitive photodetection in 2D TMDCs-based photodetectors. Recent studies have integrated perovskite nanocrystals (PNCs) layer with high optical absorbance on 2D TMDC channel in order to increase the light absorption of 2D TMDCs [2]. Still, a remaining problem is the low carrier mobility and inefficient charge injection from the PNCs layer into the TMDC layer due to the long insulating ligands of the PNCs.<br/>In this study, we address the shortcoming of conventional PNCs integrated on TMDC photodetectors by depositing in-situ core/shell perovskite onto the MoS₂channel. In-situ core/shell perovskites are formed by efficiently splitting three-dimensional (3D) perovskite films with short ligands and minimized defects, which significantly improves charge transfer and light absorption efficiency [3]. First, we optically characterized the PNCs/MoS₂ heterostructure through UV-visible absorbance spectroscopy and time resolved photoluminescence. As a result, increased optical absorbance and efficient charge transfer from the PNCs to the MoS₂ layer was confirmed. Second, we observed that the photodetection performance of PNCs/MoS₂ phototransistors were enhanced compared to the MoS₂ phototransistors without PNCs layers. Specifically, PNCs/MoS₂ phototransistors’ responsivity and specific detectivity reached the maximum values of 2.2x10⁶ A/W and 9.0x10¹¹ Jones, respectively, which were both high values compared to the previous reports. Due to the type-II band alignment of the PNCs/MoS₂ heterostructure, photogating and photoconductive effect synergistically contribute to photocurrent generation [4]. To further elucidate the photodetection mechanism of the PNCs/MoS₂ phototransistor, we changed the gate voltage while measuring the photo response of the device and we observed that the response time and the nonlinearity of the photocurrent to the incident light power increased at higher gate voltages. Both results indicate that photogating effect becomes more dominant at higher gate voltages. Our research improves the performance of the 2D MoS₂ photodetector through a simple process, which provides a promising approach for a low-cost, highly integrated, and stretchable photodetector based on 2D materials.<br/><br/><b>References </b><br/>[1] J. An et al., <i>Adv. Funct. Mater.</i> 32, 2110119 (2022).<br/>[2] H. Wu et al., <i>Adv. Sci.</i> 5, 1801219 (2018).<br/>[3] J. S. Kim et al., <i>Nature</i>, 611, 688 (2022).<br/>[4] J. Sim et al., <i>ACS Nano</i>, in press (2024).