Constructing Sensitive and Fast Lead-Free Single-Crystalline Perovskite Photodetectors Bin Yang, †,‡ Ya-Juan Li, †,‡ Yu-Xuan Tang, †,‡ Xin Mao, †,‡ Cheng Luo, †,‡ Mei-Shan Wang, ∥ Wei-Qiao Deng, †,§ and Ke-Li Han* ,†,§ † State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics (DICP), Chinese Academy of Sciences, 457 Zhongshan Road, Dalian, Liaoning 116023, China ‡ University of the Chinese Academy of Sciences, Beijing 10049, China § Institute of Molecular Sciences and Engineering, Shandong University, Qingdao 266237, P. R. China ∥ School of Physics and Optoelectronics Engineering, Ludong University, Yantai 264025, China * S Supporting Information ABSTRACT: We developed a high-performance photodetector based on (CH 3 NH 3 ) 3 Sb 2 I 9 (MA 3 Sb 2 I 9 ) microsingle crystals (MSCs). The MA 3 Sb 2 I 9 single crystals exhibit a low-trap state density of ∼10 10 cm −3 and a long carrier diffusion length reaching 3.0 μm, suggesting its great potential for optoelectronic applications. However, the centimeter single crystal (CSC)-based photodetector exhibits low responsivity (10 −6 A/W under 1 sun illumination) due to low charge-carrier collection efficiency. By constructing the MSC photodetector with efficient charge-carrier collection, the responsivity can be improved by three orders of magnitude (under 1 sun illumination) and reach 40 A/W with monochromatic light (460 nm). Furthermore, the MSC photodetectors exhibit fast response speed of <1 ms, resulting in a high gain of 108 and a gain-bandwidth product of 10 5 Hz. These numbers are comparable to the lead-perovskite single-crystal-based photodetectors. O rgano-lead perovskites have recently attracted broad attention due to their excellent optoelectronics proper- ties. 1−4 For instance, high-performance photodetectors have been developed based on organo-perovskite thin films through the solution-processed method. 3,4 Subsequently, much progress has been made during the past 3 years on further improving the responsivity, reducing the response time, and expanding the detection ranges. 5−13 Despite these progresses, the instability of perovskite thin films in air inhibits the large-scale commercial applications. 14,15 Perovskite single crystals with higher stability compared with the polycrystalline thin films have been synthesized. 16,17 These single crystals exhibit low trap-state densities, high charge-carrier mobilities, and long carrier diffusion lengths, and they are considered as potential materials for the assembling of high-performance photodetector devices. 16−31 However, the heavy metal Pb in lead-based perovskites is toxic to both humans and the environment, which is often considered as a drawback. Thus finding a stable, nontoxic, and high-performance perovskite is highly desirable. Lead-free perovskite based on Sn 2+ was first developed to replace Pb 2+ in solar cell devices. 32,33 However, the Sn 2+ -based perovskite is extremely unstable under ambient conditions and easily oxidizes from Sn 2+ to Sn 4+ . 32,33 Perovskite based on Bi 3+ and Sb 3+ with higher stability has also been developed for optoelectronics applications. 34−37 Unfortunately, the as-sub- stituted perovskite materials typically have poor device performance, which is mainly due to the high trap-state density and poor crystallinity in the polycrystalline materials. 34,37 To solve these problems, lead-free perovskite single crystals based on Sn 2+ , Bi 3+ , and Sb 3+ and double perovskite with high crystallinity and low trap-state density have been developed recently. 38−42 However, the lead-free single-crystal-based photodetectors still have some shortcomings, and the responsivity is much lower compared with that based on lead-perovskite single crystals. 40,42 For example, the (TMHD)- BiBr 5 (TMHD = N,N,N,N-tetramethyl-1,6-hexanediammo- nium) single-crystal-based photodetectors exhibit a responsivity of 0.1 A/W. 40 The Cs 2 AgInCl 6 double-perovskite single-crystal photodetectors exhibit a responsivity of 0.03 A/W. 42 Two main reasons may lead to the poor performance. One is the materials’ intrinsic poor optoelectronic properties, such as low carrier mobility and short carrier diffusion length. The carrier mobility is 0.21 cm 2 V −1 s −1 in (TMHD)BiBr 5 single crystals and 2.3 to 3.3 cm 2 V −1 s −1 in Cs 2 AgInCl 6 single crystals, which is much lower than that in lead-perovskites. 40,42 Another is the low carrier collection efficiency in these single-crystal devices, in Received: April 11, 2018 Accepted: May 23, 2018 Published: May 23, 2018 Letter pubs.acs.org/JPCL Cite This: J. Phys. Chem. Lett. 2018, 9, 3087-3092 © 2018 American Chemical Society 3087 DOI: 10.1021/acs.jpclett.8b01116 J. Phys. Chem. Lett. 2018, 9, 3087−3092 Downloaded via JINAN UNIV on November 14, 2018 at 08:52:01 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.