Achievements & milesstones

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The progress of photodetector in past year

Photodetectors (PDs), as the key component of information transmission, have recently attracted extensive attention due to their wide military and civilian applications including emitter calibration, optical communication, image sensors, and so forth. To realize photodetector basing on such requests, MIIT Key Laboratory of Advanced Display Materials and Devices focuses on developing new photoactive materials and new photodetector architecture. Below is the progress in past one year:

1). Narrowband Perovskite Photodetectors based Image Array for Potential Application in Artificial Vision (Nano letters, 2018, 18, 7628)

Image sensor arrays have been widely used in digital cameras, smartphones, and bio-robots. However, most commercial image arrays rely on the dichroic prisms or a set of interference filters to distinguish characteristic color spectrum, which significantly increases the cost and fabrication processing complexity. In this work, an ultra-narrow response photodetector with full-width at half-maximum being ~12 nm and specific detectivity over 1011 Jones at 545 nm are successfully achieved in CsPbBr3 polycrystalline films using freeze-drying casting method to adjust the surface-charge recombination. To our best knowledge, this is the narrowest spectrum response for perovskite photodetectors in the visible light waveband. More importantly, a series of narrowband photodetectors are developed to enhance diverse selectivity for target signals covering from blue light to red light via bandgap tuning in CsPbX3 by tailoring the halide component. Finally, an integrated sensing array with CsPbX3 (X=Cl, Br, I) narrowband photodetectors acting as color recognition cones is constructed, which presents clear color and shape recognition paving the way for commercialization of perovskite photodetector in electronic eyes.

 

Figure 1. Multi-color imaging systems in human visual systems and the proposed image array with series of narrowband photodetectors acting as cones.

 

2) In-Situ Formation of CsPbBr3/ZnO Bulk Heterojunction Towards Photodetector with Ultrahigh Responsivity (J. Mater. Chem. C 2018, 6, 12164)

In this study, we report a facile solution method to construct a high-performance photodetector (PD) based on in-situ formed CsPbBr3/ZnO bulk heterojunctions. Owing to the promoted charge separate and transfer at heterojunctions, the photocurrent of the CsPbBr3/ZnO PD is greatly enhanced as compared to the pristine CsPbBr3 PD, and ZnO can passivate perovskite to eliminate trap states on its surface and grain boundaries, which favors the charge carrier transport. As a result, the CsPbBr3/ZnO PD exhibits an ultrahigh responsivity of 358 A/W and a high on/off ratio of 104. In addition, the device shows a fast photoresponse (rise time: 0.88 ms and decay time: 1.53 ms). It is also revealed that the device has an excellent stability after storage for 1 month under the air. By deploying the PDs as an integrated detector array, we can acquire clear images. We believe that this work can inspire the facile and low-cost fabrication of high-performance perovskites-based optoelectronic devices for practical applications.

 

Figure 2 Schematic illustration of the imaging system and the obtained image results of the English alphabet N.

 

3) Space‐Confined Growth of CsPbBr3 Film Achieving Photodetectors with High Performance in All Figures of Merit (Adv. Funct. Mater. 2018, 28, 1804394)

All‐inorganic halide perovskite is considered as outstanding candidate of organic–inorganic hybrid perovskite due to its superior stability. However, the low solubility of precursor and uncontrollable film growth result in poor film quality and impede the application of polycrystalline films greatly. In this work it is reported on a space‐confined growth strategy to overcome the low solubility and fast crystal growth disadvantages via freezing the precursor solution within the gaps of ordered polystyrene sphere templates. Then, the dense CsPbBr3 polycrystalline films realize low trap density (3.07 × 1012 cm−3) and high carrier mobility (9.27 cm2 V−1 s−1) after stoichiometric modulation. Photodetectors based on these films exhibit high performance in all figures of merit. Specifically, high responsivity up to 216 A W−1 and ultrashort response time (<5 µs) are achieved, which are better than those of all the CsPbBr3 based PDs. A record detectivity of 7.55 × 1013 and 3.1 × 105 Hz −3 dB bandwidth are also achieved. This work opens the window of high quality all‐inorganic halide perovskite polycrystalline films and can be extended to rational application of more optoelectronic devices including solar cells, photoelectrodes, and ray detectors.

Figure 3 Schematic illustration of photodetectors basing on space‐confined growth of CsPbBr3 Film

 

4). Boosting Two-Dimensional MoS2/CsPbBr3 Photodetectors via Enhanced Light Absorbance and Interfacial Carrier Separation (ACS Appl. Mater. Interfaces, 2018, 10, 2801)

Transition metal dichalcogenides (TMDs) are promising candidates for flexible optoelectronic devices because of their special structures and excellent properties, but the low optical absorption of the ultrathin layers greatly limits the generation of photocarriers and restricts the performance. Here, we integrate all-inorganic perovskite CsPbBr3 nanosheets with MoS2 atomic layers and take the advantage of the large absorption coefficient and high quantum efficiency of the perovskites, to achieve excellent performance of the TMD-based photodetectors. Significantly, the interfacial charge transfer from the CsPbBr3 to the MoS2 layer has been evidenced by the observed photoluminescence quenching and shortened decay time of the hybrid MoS2/CsPbBr3. Resultantly, such a hybrid MoS2/CsPbBr3 photodetector exhibits a high photoresponsivity of 4.4 A/W, an external quantum efficiency of 302%, and a detectivity of 2.5 × 1010 Jones because of the high efficient photoexcited carrier separation at the interface of MoS2 and CsPbBr3. The photoresponsivity of this hybrid device presents an improvement of 3 orders of magnitude compared with that of a MoS2 device without CsPbBr3. The response time of the device is also shortened from 65.2 to 0.72 ms after coupling with MoS2 layers. The combination of the all-inorganic perovskite layer with high photon absorption and the carrier transport TMD layer may pave the way for novel high-performance optoelectronic devices.

 

Figure 4. Schematic illustration of the hybrid MoS2/CsPbBr3 photodetector.