Elsevier

Optical Materials

Volume 121, November 2021, 111586
Optical Materials

Research Article
Forming laterally structured heterojunction with FAPbI3 film for improving performance of MAPbBr3 photodetectors

https://doi.org/10.1016/j.optmat.2021.111586Get rights and content

Highlights

  • First reported MAPbBr3 single crystal coated with FAPbI3 film forms the laterally structured heterojunction.

  • a rare dual narrowband detection characteristic located at excitonic absorption of respective MAPbBr3 and FAPbI3.

  • Response time without an external electric field is 6.6 × 10−2 s.

Abstract

MAPbBr3 single crystal is coated with FAPbI3 film through the half-cladding method, which forms the laterally structured heterojunction. In comparison with pure MAPbBr3 single crystal, the optoelectronic properties of the heterojunction exhibit a rare dual narrowband detection characteristic located at excitonic absorption of respective MAPbBr3 and FAPbI3 due to the different penetration depth of light photodetection. In addition, as the applied bias voltage decreases, the charge collection efficiency at the shorter wavelength range also decreases. The self-power characteristics of the device can be attributed to the existence of the built-in electric field in the heterojunction, achieving a detectivity of 5.38 × 1012 Jones for red light at 0 V. And the fast response time without an external electric field is 6.6 × 10−2 s, which is much shorter than the reported MAPbI3/MAPbBr3 heterojunction photodetector. Our results pave the way for the simple synthesis of MAPbBr3/FAPbI3 heterojunction and their applications in photodiode and a high-performance photodetector with a fast response.

Introduction

Organic-inorganic hybrid perovskite has the advantages of adjustable optical properties, high light absorption coefficient, long-distance balanced transmission of electrons and holes [1], low cost, and increasingly simple synthesis technology. It has been widely studied in the field of optoelectronics such as solar cells [2,3], light-emitting diodes [4], lasers [5] and photodetectors [6]. Perovskite materials are usually prepared into polycrystalline or amorphous films by solution method. However, there are a lot of grain boundaries and defects in this way, resulting in the photovoltaic performance of devices greatly reduced [7]. In particular, through the deep study of the inherent characteristics of organic-inorganic hybrid perovskite APbX3 (A = CH3NH3+ (MA), or CH(NH2)2+ (FA); X = I, Br, or Cl) single crystal, it is found that it has the characteristics of comparable optimal photovoltaic quality silicon, such as long-carrier diffusion length and very low trap state density [8]. These characteristics are the basis for the huge application potential of hybrid perovskites, and make MAPbX3 single crystal becomes an ideal optoelectronic semiconductor material that is more widely used than polycrystalline thin films [9]. So far, many attempts have been made to cultivate high-quality single crystals with centimeter size.

During the single crystal growth process, the difference in solubility of MABr and PbBr2 in N, N-dimethylformamide (DMF) can lead to the presence of internal impurities, holes, bubbles and non-stoichiometric MAPbBr3, which will undoubtedly affect the performance of optoelectronic devices. Therefore, the researchers found that MABr and PbBr2 with a molar ratio of 0.8 can improve this problem [10]. Generally, perovskite materials maybe absorb photons with larger photon energy than their band gaps, prevents theirs application in other wavelength ranges. A useful way to solve this problem is to expand the optical absorption by introducing materials that absorb other wavelengths of light [11,12]. Synthesized large-size MAPb(BrxI1-x)3 single crystal exhibited the photoelectric detection in the 405–710 nm band, where bromine rich single crystals have a higher light dark response ratio [13]. Bi doped heterojunction was fabricated by epitaxial growth of one side on the MAPbBr3 single crystal, and then the PN junction is formed through the photoelectric analysis. Compared with the single crystal photodetector, the performance of the constructed photodiode is improved [14]. A simple two-step method has been developed to fabricate MAPbBr3/MAPbIxBr3-x heterojunction to explore the structure optimization of perovskite-based single crystal photodetectors. This work demonstrated an order of magnitude higher responsivity than that of a single crystal at 0 V, which may lead to a more effective self-powered heterojunction system [15]. As a new type of light-harvesting materials, FAPbI3 is known to possess excellent optoelectronic properties even exceeding those of MAPbI3 [16]. Because the larger FA cation occupies the A site of the ABX3 type perovskite, the FAPbI3 has a smaller optical bandgap than that of MAPbI3 [17]. Meanwhile, FAPbI3 also exhibits a wider absorption spectrum and better thermal stability [18]. Here, we choose MAPbBr3 single crystal coating with FAPbI3 to form laterally structured heterojunction, which is rarely discussed, still worth studying to improve device performance and develop application characteristics.

In this work, millimeter-sized MAPbBr3 single crystal is synthesized by inverse temperature crystallization method. And then laterally structured heterojunction is formed with coating FAPbI3, which possesses a smaller bandgap and even allows near-infrared light absorption. Compared with pure MAPbBr3 single crystal, the optoelectronic properties of the heterojunction exhibit a rare dual narrowband detection characteristic, which corresponding to the excitonic absorption of MAPbBr3 and FAPbI3, respectively. In general, the narrow-band light response in the entire spectral range is closely related to the charge diffusion length and light penetration length. The results of the light responsivity, detectivity and the self-powered response show that the device exhibits good diode characteristics with a light responsivity in the range of 400–830 nm and achieves a detectivity of 5.38 × 1012 Jones for red light at 0 V.

Section snippets

Materials and chemicals

Lead bromide (PbBr2, 99%), lead iodide (PbI2, 98%), N, N-dimethylformamide (DMF, 99.5%) and Formamidine iodide (FAI, 99.0%) were purchased from Macklin. Methylamine bromide (MABr, 99.5%) was purchased from Xi'an Polymer Light Technology Corp. All reagents were used as received without further purification.

Material growth and device fabrication

The preparation procedures of perovskite heterojunction are demonstrated in Fig. 1a. Here, MAPbBr3 single crystal growth adopts inverse temperature crystallization method [19]. First,

Basic characterization

XRD data was collected using the X-ray diffractometer (PANalytical, X'Pert PRO) with Cu Kα radiation (λ = 0.15 nm). The X-ray diffraction pattern of the grown MAPbBr3 single crystal after grinding into powder can correspond to the reported standard card [21] as shown in Fig. 1b. The FAPbI3 powder is scraped from the heterojunction, and the X-ray diffraction pattern confirms the existence of diffraction angles similar to those of pure FAPbI3 [22] and MAPbBr3 crystal planes [23]. The slightly

Conclusion and prospect

In summary, a simple two-step method of immersing half of the MAPbBr3 single crystal in the FAPbI3 precursor solution followed by annealing treatment is used to prepare the MAPbBr3/FAPbI3 heterojunction. The dark current of the device is as low as 6.41 × 10−7 mA at 4 V. At the same time, the MAPbBr3/FAPbI3 heterojunction photodetectors have good spectral sensitivity in the green (552–580 nm) and red (725–800 nm) parts at 2.0 V, respectively. In addition, the detection rate of the device is

CRediT authorship contribution statement

Minmin Zhang: Data curation, Formal analysis, Writing original draft. Wu Lifang: Conceptualization, Software. Shunfa Gong: Methodology, Software, Validation. Qiuju Han: Writing review & editing. Wenzhi Wu: Writing original draft, Supervision, Funding acquisition.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgment

The authors are grateful for the financial support from Key Project of Scientific Foundation by Heilongjiang Province (ZD2018014), Young scholar innovation team of Heilongjiang University (RCYJTD201901).

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