With the continuous expansion of the application of photodetectors in traditional sensing, communication, imaging fields, as well as emerging fields such as flexible robotics and artificial intelligence, the demand for photodetectors is increasing. Particularly, for some new application scenarios, the self-powering capability and sensitivity to polarization information of photodetectors have become increasingly important. However, it is difficult for photodetectors based on single-component active layers to simultaneously meet all these requirements. In contrast, employing carefully designed heterogeneous structures with different optoelectronic properties of materials is a highly effective means to achieve multiple advantages of photodetectors. By composing heterogeneous structures with materials of different optoelectronic performances, the advantages of various materials can be fully utilized, enabling flexibility, self-powering capability, and sensitivity to polarization information in photodetectors. This approach provides new possibilities for the design and performance enhancement of photodetectors, and is expected to further promote their development in various application fields.
Although heterostructures of perovskite and other materials have achieved various high-performance photodetectors and have been widely applied in imaging, detection, and sensing fields, seamlessly combining two perovskite materials into lateral heterostructures still remains challenging. The methods for preparing lateral heterogeneous structures of traditional inorganic semiconductors are difficult to directly apply to perovskite materials that are sensitive to solvents and environments. Moreover, in the process of preparing lateral heterogeneous structures by solution methods, the material deposited first is easily dissolved by subsequent solvents. To address the solvent orthogonality issue in the preparation process of perovskite lateral heterostructures, the team has designed a selective anion-exchange scheme to fabricate high-quality perovskite micro-wire lateral heterostructures. Benefiting from the high crystal quality and perfectly bonded heterostructure interfaces, the fabricated photodetector exhibits a responsivity (R) of 748 AW-1 and a detectivity (D) of 8.2×1012 Jones. Additionally, the device demonstrates high sensitivity to polarization, with a dichroic ratio of 5.6. After being exposed to air for 144 days, the device still maintains 81% of its performance. Relevant research results were recently published in Photonics Research, Volume 11, No. 12, 2023[Shun-Xin Li, Jia-Cheng Feng, Yang An, Hong Xia. Flexible, self-powered, and polarization-sensitive photodetector based on perovskite lateral heterojunction microwire arrays[J]. Photonics Research, 2023, 11(12): 2231]
The process for preparing perovskite micro-wire lateral heterostructures by selective anion exchange is illustrated in Figure 1(a). The PDMS template and substrate form independent microchannel arrays, finely adjusting and limiting the flow direction and position of precursor solution. After the solvent gradually evaporates completely, the independent liquid stripes transform into independent crystal arrays. By taking advantage of the reconfigurable nature of perovskite's anion bonding, high-quality heterostructures are easily achieved through anion exchange. To achieve regionally selective anion exchange, half of the PDMS is peeled off, exposing high-quality micro-wires, while the other half remains on top of the crystals to avoid particle exchange. Subsequently, this system is exposed to an HI atmosphere. As the exposure time increases, the Br in the (PEA)2PbBr4 crystals exposed to the HI atmosphere is gradually replaced by I, forming (PEA)2PbBr4-xIx, while the protected crystals by PDMS remain unchanged in composition. After the substitution process is completed, the other half of the PDMS membrane is removed, resulting in a high-quality and highly ordered (PEA)2PbBr4—(PEA)2PbBr4-xIx lateral heterostructure array with a clear interface.
Based on this high-quality lateral heterostructure, the fabricated photodetector achieves a high responsivity of 748 AW-1 (5 V) and 13.5 AW-1 (0 V). For linearly polarized light, the device exhibits a dichroic ratio of 5.6. Furthermore, this photodetector can maintain 86% of its performance even after being exposed to air for a month.
In many practical applications, the polarization state of light contains useful information. Polarization refers to the directional orientation of the oscillation direction of light waves, and the polarization state has important effects on the propagation, reflection, and absorption processes of light. Therefore, sensitive detection of the polarization state of light can help us obtain more information about light, thereby expanding the range of optical technology and sensing applications. Polarization-sensitive photodetectors can be used to measure the polarization state of light, and are applied in fields such as optical communication, optical imaging, astronomy, and biomedical imaging. Therefore, the importance of polarization-sensitive photodetectors lies in their ability to help us comprehensively understand and apply polarization information of light, thereby promoting the development and application of optical technology in various fields. The preparation of perovskite lateral heterostructures not only enables high-performance photodetectors, but also helps to enhance the polarization sensitivity of photodetectors.
Figure 1(a) The schematic process of preparing perovskite micro-wire lateral heterostructures using region-selective anion exchange. (b)The photocurrent and R value of the lateral heterostructure-based photodetector under varying levels of illumination intensity. (c) The variation curve of photocurrent in response to different polarization states of light. (d) The photocurrent variation curve of the device after being stored in air for different durations.
The preparation of perovskite lateral heterostructures is challenging mainly due to several reasons, including material matching, growth control, and interface alignment. Perovskite materials are usually composed of different metal ions, and different metal ions can lead to changes in lattice structure and physical properties. Therefore, when preparing perovskite lateral heterostructures, it is necessary to consider the compatibility between materials to ensure good crystallization and contact at the interface. The growth process of perovskite materials is influenced by many factors such as temperature, pressure, solution concentration, solvent selection, etc. To obtain high-quality perovskite lateral heterostructures, these parameters need to be precisely controlled to achieve suitable growth conditions. In addition, the preparation of perovskite lateral heterostructures also needs to consider the issue of interface alignment because the lattice structures and crystal orientations of different materials may not be completely matched. Therefore, the preparation of perovskite lateral heterostructures is challenging and requires precise control of key factors such as crystal growth process. By selecting the scheme of region-selective anion exchange, high-quality lateral heterostructure arrays can be prepared and promoted for their application in optoelectronic devices.
In the next step, the team will optimize the composition of lateral heterostructures, such as using lead-free perovskites to prepare lateral heterostructures, to achieve environmentally friendly optoelectronic devices. The team will also study the physical and chemical mechanisms of anion exchange process, laying the foundation for achieving high-performance polarization-sensitive photodetectors.
