COMMUNICATION 1800152 (1 of 8) © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.advopticalmat.de High-Performance Low-Voltage-Driven Phototransistors through CsPbBr 3 –2D Crystal van der Waals Heterojunctions Chengxue Huo, Xuhai Liu, Ziming Wang, Xiufeng Song,* and Haibo Zeng* DOI: 10.1002/adom.201800152 Kang et al. demonstrated a high-perfor- mance photodetector based on MoS 2 / perovskites hybrid structure, [5] however, with the CH 3 NH 3 PbI 3 thin film directly spin-coated onto MoS 2 to enhance the absorption of light. Qian et al. have fab- ricated phototransistors with a hybrid channel material of nitrogen-doped gra- phene quantum dot–modified perovskite and a mildly reduced graphene oxide. [6] However, either the perovskites or the 2D materials can directly bridge across the transistor channel. Liu et al. also reported similar perovskite/MoS 2 hybrid thin film transistors by vacuum deposition of perovskites. [7] A large number of grain boundaries in the perovskite thin films could hinder the potential performance improvement in these devices. Most importantly, the VDWH configuration has not been fully realized in the abovemen- tioned hybrid structures, because certain portion of the charge carriers can directly flow from one metal electrode to the opposite electrode without transporting through the heterojunction part of the device. Recently, Ou et al. achieved a strong depletion-induced lateral p–n junction by local electronic doping at the surface of indi- vidual CH 3 NH 3 PbI 3 nanosheets. [8] Although the heterojunc- tion can play an adjustment role in this device, it is still not a standard perovskite/2D material VDWH. To fully realize a perovskite/2D material VDWH, Niu et al. used van der Waals epitaxy to deposit CH 3 NH 3 PbI 3 on different 2D materials. However, corresponding optoelectronic devices were not reported. [9] After that, Cheng et al. have reported a gra- phene/CH 3 NH 3 PbI 3 /graphene heterojunction photodetector by making use of the layered characteristic of lead iodide (PbI 2 ) and vapor-phase intercalation. [10] Tan et al. have used graphene as the protective layer to achieve the 2D (C 4 H 9 NH 3 ) 2 PbBr 4 crystal photodetectors via electron beam lithography and plasma etching. [11] However, these device preparing methods are very tedious. Therefore, a universal and cheap method should be proposed to fully realize the heterojunction devices combining perovskite thin single crystals and 2D semiconductors. Herein, we have first found that the optical properties of various CsPbBr 3 /2D heterojunctions significantly differ because of the different band alignments. Next, to further explore the strong driving force existing in CsPbBr 3 /2D het- erojunction to separate the excited electron–hole pairs, a phototransistor based on this heterojunction was fabricated by a gentle dry transfer technique. Due to the strong driving Combining halide perovskites and 2D materials to form heterojunctions is a potential excellent strategy to design high-performance phototransistors. However, a standard perovskite/2D material heterojunction is not fully realized, because either of the active material usually directly bridges across the opposite metal electrodes in the transistor platform. Here, phototransistors are fabricated based on high-quality van der Waals grown CsPbBr 3 and MoS 2 , in which CsPbBr 3 and MoS 2 are overlapped only within the transistor channel. The phototransistors based on this standard CsPbBr 3 / MoS 2 heterojunction exhibit excellent optical detection ability and field-effect characteristics at a drain–source voltage as small as 0.5 V. The rise and fall times of the phototransistor are 2.5 and 1.8 ms, respectively. The hole mobility is calculated to be 0.08 cm 2 V -1 s -1 in darkness, and 0.28 cm 2 V -1 s -1 under the 442 nm laser illumination. All of the measurements are conducted at room temperature in ambient air, indicating the excellent robustness of the CsPbBr 3 /MoS 2 heterojunction. This work provides a new strategy to minimize the device size by using low-voltage-driven, air-stable perovskite/2D material heterojunctions. Dr. C. X. Huo, Dr. X. H. Liu, Dr. Z. M. Wang, Prof. X. F. Song, Prof. H. B. Zeng MIIT Key Laboratory of Advanced Display Materials and Devices Institute of Optoelectronics & Nanomaterials College of Material Science and Engineering Nanjing University of Science and Technology Nanjing 210094, China E-mail: xiufengsoong@njust.edu.cn; zeng.haibo@njust.edu.cn The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adom.201800152. Perovskite Phototransistors van der Waals heterojunctions (VDWHs) have attracted tre- mendous attentions because 2D material–based VDWHs enable the combination of different materials, [1] which provides new strategies to design novel high-performance devices, such as tunneling transistors, photodetectors, photovoltaics, and light-emitting diodes. [2] The VDWH devices could show excel- lent performance driven by a low external voltage, which could minimize the device size and the power dissipation, leading to great application prospects in terms of low-cost flexible and wearable electronics. [3] Meanwhile, metal halide perovskites with ABX 3 structure have been also widely applied in optoelectronic devices for their excellent properties, such as large absorption coefficient, tun- able bandgap, and high photoluminescence quantum yield. [4] Halide perovskites have been integrated into hybrid configura- tions to further explore their unique properties. For example, Adv. Optical Mater. 2018, 1800152