High-Performance All-Inorganic Tin-Lead Perovskite Photodetectors Enabled by All-in-One Engineering for Intelligent Agriculture Light Monitoring.

<sec>Photodetector occupies an important position in the sensor family, but most of the photoelectric conversion materials of photodetectors are inorganic semiconductors, such as GaAs, GaN, Ge and Si, these inorganic semiconductors are usually prepared by complicated methods and high cost, and furthermore, they have poor mechanical flexibility. Organic-inorganic hybrid perovskite materials serving as visible-light sensitizers have the advantages of balanced electron and hole mobilities, adjustable bandgaps, high absorption coefficients, low temperature solution preparation, which make the materials a suitable candidate for inorganic semiconductors.</sec><sec>For planar photodetectors, carriers have greater probabilities to be trapped by the defects in the perovskite films, therefore it is important to fabricate a high-quality perovskite film. However, owing to the low formation energy of perovskite crystals, defects prove to occur on the film surface and grain boundaries, which aggravate the performance of perovskite optoelectronic devices. In this work, we introduce a small quantity of graphene oxide nanosheets (GOSs) on bare glass substrate as effective nucleation sites of perovskite crystals. Owing to the extremely low density of GOSs and large exposed glass basement, the GOSs cannot be regarded as an interface layer. The existence of GOSs on smooth substance reduces the perovskite nucleation barrier, leading to a more preferential crystal growth in these locations, and binds tightly with glass substrate, which passivates the defects efficiently. Meanwhile, the element of O in the GOSs can create Pb–O bond with Pb in the CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>, further improving the crystal of perovskite. On this basis, planner perovskite photodetector with a structure of glass/GOSs/CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>/MoO<sub>3</sub>/Au is fabricated. By adjusting the concentration of GOSs deionized water dispersion under the same spin-coating condition, the photoelectric conversion performance of perovskite photodetector is enhanced. Under the influence of the optimal concentration of GOSs, photocurrent of the champion photodetector (1.15 × 10<sup>–6</sup> A) is an order of magnitude higher than that of reference device without GOSs modified (3.58 × 10<sup>–7</sup> A) at 3 V bias, leading to a high ON/OFF current ratio of 5.22 × 10<sup>3</sup>. Besides, improved photoresponse speed is also found in the champion device, with a rise time of 9.6 ms and a decay time of 6.6 ms, respectively. The enhanced performance of GOSs modified perovskite photodetector can be attributed to the significantly reduced defects bringing about an enhanced charge separation and collection performance in the CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> films.</sec><sec>By introducing extremely low quantity GOSs as the effective perovskite crystal nucleation sites, the perovskite crystallization and thin film can be effectively improved, leading to a positive effect on the performance of perovskite photodetector. This method has a certain universality, and therefore it has a reference value for other structures of perovskite photoelectric devices.</sec>

Realization of remote wearable health monitoring (RWHM) technology for the flexible photodiodes is highly desirable in remote-sensing healthcare systems used in space stations, oceans, and forecasting warning, which demands high external quantum efficiency (EQE) and detectivity in NIR region. Traditional inorganic photodetectors (PDs) are mechanically rigid and expensive while the widely reported solution-processed mixed tin-lead (MSP) perovskite photodetectors (PPDs) exhibit a trade-off between EQE and detectivity in the NIR region. Herein, a novel functional passivating antioxidant (FPA) strategy has been introduced for the first time to simultaneously improve crystallization, restrain Sn2+ oxidization, and reduce defects in MSP perovskite films by multiple interactions between thiophene-2-carbohydrazide (TAH) molecules and cations/anions in MSP perovskite. The resultant solution-processed rigid mixed Sn-Pb PPD simultaneously achieves high EQE (75.4% at 840 nm), detectivity (1.8 × 1012 Jones at 840 nm), ultrafast response time (trise /tfall = 94 ns/97 ns), and improved stability. This work also highlights the demonstration of the first flexible photodiode using MSP perovskite and FPA strategy with remarkably high EQE (75% at 840 nm), and operational stability. Most importantly, the RWHM is implemented for the first time in the PIN MSP perovskite photodiodes to remotely monitor the heart rate of humans at rest and after-run conditions.

Cesium lead bromide (CsPbBr3) perovskite photodetectors (PDs) are attractive for applications in visible light communication (VLC) due to ultra‐high detectivity and fast response speed. However, the fabrication of high‐quality CsPbBr3 polycrystalline films using solution‐based process is very challenging. Due to the low solubility of CsBr in precursor solutions, solution‐processed CsPbBr3 films are typically discontinuous and porous, hindering the performance of resulting PDs. Herein, a facile and modified sequential spin‐coating method is introduced to prepare high‐crystallinity, pinhole‐free CsPb2Br5‐CsPbBr3 perovskite films with an average grain size of ≈1 µm. The hole‐transport‐layer‐free (HTL‐free) PDs based on the CsPb2Br5‐CsPbBr3 perovskite films show high performance parameters, including the responsivity of 0.11 A W−1, the detectivity of 1.4 × 1012 Jones, a linear dynamic range of 128.6, and an on/off ratio of 1.5 × 106. The PDs outperform other HTL‐free perovskite PDs and are comparable to the p–i–n perovskite PDs reported in the literature. In addition, the high‐performance CsPb2Br5‐CsPbBr3 PDs are applied in VLC by using the PD as a self‐powered signal receiver of voice commands in a simulated room. This work uniquely combines the features of high‐performance self‐powered perovskite PDs with VLC techniques, paving the path to wide applications of all‐inorganic perovskite PDs.

The preparation of high-quality perovskite films with optimal morphologies is important for achieving high-performance perovskite photodetectors (PPDs). An effective strategy to optimize the morphologies is to add antisolvents during the spin-coating steps. In this work, an environment-friendly antisolvent ethyl acetate (EA) was employed to improve the quality of perovskite films, which can effectively regulate the formation of an intermediate phase staged in between a liquid precursor phase and a solid perovskite phase due to its moderate polarity, and further promote the homogeneous nucleation and crystal growth in the subsequent annealing process, thus leading to the formation of high-quality perovskite films and enhanced photodetector (PD) performance. As a result, the responsivity of the PPDs reached 0.85 A W-1 under the illumination of 532 nm laser with the power density of 6.37 μW cm-2 at bias voltage of -2 V. The corresponding detectivity reached 3.27 × 1011 Jones, while the rise time and fall time are 256 ns and 370 ns, respectively. These results demonstrates that our developed solution-processed method with EA as antisolvent has remarkably advantages for the fabrication of high-performance PPDs and can provide a reference for the other similar research work.

Recently, organic metal halide perovskites have attracted wide attention in the field of photovoltaic devices due to series of excellent photoelectric properties. However, the device performance is limited by a large number of surface defects in the perovskite film. Finding an effective method for defect passivation of perovskite film is considered to be a preferred strategy to further improve the performance of perovskite photovoltaic devices. Here, we use an organic metal salt, sodium alginate (SA), to passivate the surface defects of perovskite films to prepare high-performance perovskite photodetectors (PePDs). We find that the introduction of SA can improve the quality of perovskite active layer and passivate the surface defects effectively, which reduce the carrier recombination probability to increase the photocurrent and reduce the dark current of the PePDs. And the detectivity (D*) at 600 nm reaches 3.6×10¹² Jones, three times that of the controlled devices. Meanwhile, the PePDs doped with sodium alginate have better stability and device life, which remains 82% of the original performance after being placed in the atmosphere for 7 days. These results indicate that it is an effective strategy to passivate perovskite film with organic metal salt to prepare high-performance PePDs.

Enhanced performance of perovskite photodetectors fabricated by two-step spin coating approach

Perovskite photodetectors (PPDs) offer a promising solution with low cost and high responsivity, addressing the limitations of traditional inorganic photodetectors. However, there is still room for improvement in terms of the dark current and stability of air-processed PPDs. In this study, 4,4',4''-tris(carbazol-9-yl)-triphenylamine (TCTA) was utilized as a nucleation agent to enhance the quality of perovskite films. The synergistic effect of TCTA and moisture promotes rapid nucleation of PbI2-PbCl2, resulting in an increased nucleation rate and the elimination of pinholes in the film. By employing additive engineering, we obtained a PbI2-PbCl2 layer with high coverage, leading to a low density of traps in the corresponding perovskite film. Consequently, the modified PPD exhibits a remarkable reduction in dark current density by over one order of magnitude, reaching 2.4 × 10-10 A cm-2 at -10 mV, along with a large linear dynamic range (LDR) of 183 dB. Furthermore, the resulting PPD demonstrates remarkable stability, retaining 90% of the initial external quantum efficiency (EQE) value even after continuous operation for over 3200 hours. Owing to a fast response time in the nanosecond range, the PPD could convert modulated light signals into electrical signals at a speed of 588 Kbit s-1, highlighting the great potential in the field of optical communication.

High-quality CH3NH3PM3 perovskite thin films in air via doctor-blading technology of in-situ heat treatment were prepared, the resulting perovskite film has the advantages of large crystal domains, good stability and repeatability. Based on the perovskite film, the perovskite photodetectors with such a simple structure of glass/ CH3NH3PbI3/Au were constructed, and the high resulting responsivity (R) of 5.70 AW−1 was achieved, the as fast as rise and fall response speed of 14.0ms and 13.4ms were showed, which indicates that the perovskite films via doctor- blading have a potential application prospect in constructing low-cost and large-area optoelectronic devices.

Effect of Ag nanoparticles on performance of CH3NH3PbI3 perovskite photodetectors

The preparation of high-quality perovskite films with optimal morphologies is important for achieving high-performance perovskite photodetectors (PPDs). An effective strategy to optimize the morphologies is to add antisolvents during the spin-coating steps. In this work, a novel environment-friendly antisolvent tert-amyl alcohol (TAA) is employed first to improve the quality of perovskite films, which can effectively regulate the formation of an intermediate phase staged in between a liquid precursor phase and a solid perovskite phase due to its moderate polarity and further promote the homogeneous nucleation and crystal growth, thus leading to the formation of high-quality perovskite films and enhanced photodetector performance. As a result, the responsivity of the PPD reaches 1.56 A/W under the illumination of 532 nm laser with the power density of 6.37 μW / cm 2 at a bias voltage of − 2 V , which is good responsivity for PPDs with the vertical structure and only CH 3 NH 3 PbI 3 perovskite as the photosensitive material. The corresponding detectivity reaches 1.47 × 10 12 Jones, while the linear dynamic range reaches 110 dB. These results demonstrate that our developed green antisolvent TAA has remarkable advantages for the fabrication of high-performance PPDs and can provide a reference for similar research work.

Fully-printed, flexible cesium-doped triple cation perovskite photodetector

2D Ruddlesden-Popper perovskite ferroelectric film for high-performance, self-powered and ultra-stable UV photodetector boosted by ferro-pyro-phototronic effect and surface passivation

Organic-inorganic hybrid perovskite films possess superior optoelectronic properties, including bandgap tunability, high absorption coefficient, well-balanced charge carrier mobility and long electron-hole diffusion length. Hence it can serve as sensitizers in solar cells, photodetectors, pumped lasers and light-emitting diodes. However, the crystallographic defect passivation and suppression of organic-inorganic hybrid perovskite at the grain boundaries are crucial for efficient and stable perovskite photodetectors (PPDs). Herein, a bulk heterojunction (BHJ) fabricated by the two-step spin-coating method facilitates high-quality perovskite film formation while reducing the non-radiative recombination within the photoactive layer, enhancing the photosensitivity performance of PPDs based on BHJ configuration. Specifically, sulfonated graphene (SGA) was used as a functional passivator to interact with Pb²⁺ at the surface and grain boundaries due to its large specific surface area and high binding energy with lead ion, thereby ameliorating the device stability and carrier transport capacity within perovskite films, resulting in a lower dark current density and a higher photocurrent density. Consequently, the PPD based on the BHJ configuration achieves a responsivity of 570 mA/W and the specific detectability of 6.3×10¹¹ Jones under the bias voltage of −1 V with the 532 nm laser illumination intensity of 0.5 μW/cm² and a linear dynamic range of 126 dB. The PPD based on BHJ configuration shows ultrahigh response rates of 0.3 μs and 52.7 μs for the rise and fall times at zero bias, respectively, which is attributed to efficient carrier extraction and the lower defect density. The grain boundary passivation strategy of SGA modification develops a practical approach to ameliorate PPD performance and stability.

Ultrasensitive Heterojunctions of Graphene and 2D Perovskites Reveal Spontaneous Iodide Loss

Plasmonic hole-transport-layer enabled self-powered hybrid perovskite photodetector using a modified perovskite deposition method in ambient air