Narrowband photodetectors are widely applied in color image recognition, machine vision, biological sensing, image processing, and other applications. A conventional narrowband photodetector is a combination of a broadband photodetector and a series of optical filters, which significantly increases the device cost, architectural complexity, and energy loss. Therefore, to circumvent this issue, several filter-free approaches are established, including utilization of materials with narrowband absorption, charge collection narrowing (CCN) concept, plasmonic effect, and perovskite/polymer synergetic layers. Among these approaches, perovskite(PVSK) narrowband optoelectronic devices based on metal nanoparticles (MNP) are a topic of significant interest in the fields of solar cells and photodetectors, which incorporate enhanced light via the surface plasmon resonance (SPR) of MNP into the excellent optoelectronic properties of perovskite (high absorption coefficient, long carrier separation distance, high carrier mobility, and adjustable optical broadband). However, the quality of the perovskite film degrades when MNP is integrated with the device that is in direct contact with the perovskite film. One of the ways to solve this problem is to introduce an intermediate layer between PVSK and MNP for film quality. In this study, the polymethylmethacrylate (PMMA) membrane is introduced between perovskite and silver island films, and a new structure of a narrowband enhanced perovskite photodetector is proposed. The device performance can be improved by varying the perovskite precursor solution temperature and thickness of the perovskite.
The narrowband-enhanced perovskite photodetector is fabricated as follows. First, the thin silver film is deposited on a glass substrate via physical vapor deposition, and the silver nanoisland film (Ag NF) is prepared via annealing at 300 ℃ for 30 min. The average diameter of the Ag NPs is approximately 80 nm. Subsequently, the PMMA intermediate layer is spun on the surface of Ag NF, the perovskite film is spun on the PMMA via spin-coating, and silver electrodes with a thickness of 100 nm are deposited on the perovskite film via thermal evaporation. The narrowband-enhanced perovskite photodetector has a planar structure of SiO2/Ag NF/PMMA/perovskite. The thickness of the PMMA interlayer is controlled by varying the spin-coating speed and the concentration of the PMMA solution. The grain size and thickness of the perovskite films are governed by the perovskite precursor solution temperature and spin-coating speed, respectively.
The influence of PMMA thickness on the narrowband bandwidth is investigated in the experiment. The central wavelength of the narrowband response spectrum is approximately 490 nm. The lowest transmissivity decreases with the addition of the PMMA film. The transmissivity first decreases and then increases as the thickness of PMMA increases, where destructive interference occurs via the PMMA film (Fig. 4). The effect of the perovskite precursor solution temperature on the grain size of perovskite films is investigated. The scanning electron microscope (SEM) images (Fig. 5) show that the grain size of the perovskite first increases and then decreases with increasing temperatures, and the maximum grain diameter is ~5 μm at 60 ℃, which has the higher photocurrent. Moreover, the thickness of the perovskite film is analyzed under the optimization experimental conditions (temperature of 60 ℃, thickness of 278 nm). When the spin-coating speed is 5000 r/min, the maximum photocurrent and large photocurrent gain are obtained (Fig. 6). The performance of the device at optimal parameters (Fig. 7) is characterized. Subsequently, this performance is compared with those of the reported filter-free narrowband photodetectors, as summarized in Table 1.
Herein, a narrowband perovskite photodetector based on the surface plasmon resonance of the silver island film is prepared, and the narrowband of the photodetector is enhanced by introducing thin film between the perovskite and silver island films. The grain size of the perovskite films is governed by the perovskite precursor solution temperature, and the light propagation path is controlled by the thickness of the perovskite to improve the narrowband response. The effects of the PMMA film thickness, precursor solution temperature, and perovskite thickness on the performance of the detector are investigated. The as-prepared photodetector with optimized parameters exhibits a narrow photo-response peak centered at approximately 490 nm with a full width at half maximum of 110 nm, as well as a high responsivity of 0.6 A·W-1 at an applied bias voltage of 2 V, high external quantum efficiency of 159%, normalized detectivity of 2.73×1013 cm·Hz1/2·W-1, and response time of 247 ms(rise time)/266 ms(fall time). The detector presented in this paper has a simple fabrication process, particularly in the control method, and exhibits high performance, thus presenting a new strategy for the fabrication of narrowband photodetectors.
