Aqueous-Phase Formation of Two-Dimensional PbI2 Nanoplates for High-Performance Self-Powered Photodetectors.

The process of the aqueous synthesis of nanomaterials has gained considerable interest due to its ability to eliminate the need for complex organic solvents, which aligns with the principles of green chemistry. Fabricating nanostructures in aqueous solutions has gained recognition for its potential to develop ultrasensitive, low-energy, and ultrafast optoelectronic devices. This study focuses on synthesizing lead iodide (PbI2) nanoplates (NPs) using a water-based solution technique and fabricating a planar photodetector. The planar photodetectors (ITO/PbI2 NPs/Au) demonstrated a remarkable photosensitivity of 3.9 × 103 and photoresponsivity of 0.51 mA/W at a wavelength of 405 nm. Further, we have carried-out analytical calculations for key performance parameters including open-circuit voltage (Voc), short-circuit current (Isc), on-off ratio, responsivity (R), and specific detectivity (D*) at zero applied bias, while photodetector operating in self-powered mode. These values are as follows: Voc = 0.103 V, Isc = 1.93 × 10-8, on-off ratio = 103, R = 4.0 mA/W, and D* = 3.3 × 1011 Jones. Particularly, the asymmetrical output properties of ITO/PbI2 NPs/Au detector provided additional evidence of the effective creation of a Schottky contact. Therefore, the photodetector exhibited a photo-response even at 0 V bias (rise/decay time ~1 s), leading to the realization of self-powered photodetectors. Additionally, the device exhibited a rapid photo-response of 0.23/0.38 s (-5 V) in the visible range. This study expands the scope of aqueous-phase synthesis of PbI2 nanostructures, enabling the large-area fabrication of high-performance photodetectors.

YCl3-Substituted CsPbI3 Perovskite Nanorods for Efficient Red-Light-Emitting Diodes.

Cesium lead iodide (CsPbI3) perovskite nanocrystals (NCs) are a promising material for red-light-emitting diodes (LEDs) due to their excellent color purity and high luminous efficiency. However, small-sized CsPbI3 colloidal NCs, such as nanocubes, used in LEDs suffer from confinement effects, negatively impacting their photoluminescence quantum yield (PLQY) and overall efficiency. Here, we introduced YCl3 into the CsPbI3 perovskite, which formed anisotropic, one-dimensional (1D) nanorods. This was achieved by taking advantage of the difference in bond energies among iodide and chloride ions, which caused YCl3 to promote the anisotropic growth of CsPbI3 NCs. The addition of YCl3 significantly improved the PLQY by passivating nonradiative recombination rates. The resulting YCl3-substituted CsPbI3 nanorods were applied to the emissive layer in LEDs, and we achieved an external quantum efficiency of ~3.16%, which is 1.86-fold higher than the pristine CsPbI3 NCs (1.69%) based LED. Notably, the ratio of horizontal transition dipole moments (TDMs) in the anisotropic YCl3:CsPbI3 nanorods was found to be 75%, which is higher than the isotropically-oriented TDMs in CsPbI3 nanocrystals (67%). This increased the TDM ratio and led to higher light outcoupling efficiency in nanorod-based LEDs. Overall, the results suggest that YCl3-substituted CsPbI3 nanorods could be promising for achieving high-performance perovskite LEDs.

Interlayer of PMMA Doped with Au Nanoparticles for High-Performance Tandem Photodetectors: A Solution to Suppress Dark Current and Maintain High Photocurrent.

Currently, colloidal quantum dots (CQDs)-based photodetectors are widely investigated due to their low cost and easy integration with optoelectronic devices. The requirements for a high-performance photodetector are a low dark current and a high photocurrent. Normally, photodetectors with a low dark current also possess a low photocurrent, or photodetectors with reduced dark current possess a reduced photocurrent, resulting in low detectivity. In this paper, a solution to suppress dark current and maintain a high photocurrent, i.e., use of poly(methyl methacrylate) doped with Au nanoparticles (NPs) (i.e., PMMA:Au) as an interlayer for enhanced-performance tandem photodetectors, is presented. Our experimental data showed that the dark current through the tandem photodetector ITO/PEDOT:PSS/PbS:CsSnBr3/ZnO/PMMA:Au/CuSeN/PbS:CsSnBr3/ZnO/Ag is suppressed significantly; meanwhile, a high photocurrent is maintained after a PMMA:Au interlayer has been inserted between two subdetectors. The inserted PMMA:Au interlayer acts as storage nodes for electrons, reducing the dark current through the device; meanwhile, the photocurrent can be enhanced under illumination. As a result, the specific detectivity of the tandem photodetector with 35 nm PMMA:Au interlayer was enhanced significantly from 5.01 × 1012 to 2.7 × 1015 Jones under 300 µW/cm2 532 nm illumination at a low voltage of -1 V as compared to the device without a PMMA:Au interlayer. Further, the physical mechanism of enhanced performance is discussed in detail.

Self-powered, all-solution processed, trilayer heterojunction perovskite-based photodetectors.

Heterostructures composed of nano-/micro-junctions, combining the excellent photon harvesting properties of nano-systems and the ultrafast carrier transfer of micro-systems, have a promising role in high-performance photodetectors. In this paper, a highly-sensitive trilayer self-powered perovskite-based photodetector ITO/ZnO (70 nm)/CdS (150 nm)/CsPbBr3 (200 nm)/Au, in which the CdS nanorods (NRs) layer is sandwiched between a ZnO/CsPbBr3 interface to reduce the interfacial charge carriers' recombination and the charge transport resistance, is presented. Due to the strong built-in potential and the internal driving electric-field, an ultra-high On/Off current ratio of 106 with a responsivity of 86 mA W-1 and a specific detectivity of 6.2 × 1011 Jones was obtained at zero bias under 85 µW cm-2 405 nm illumination and its rise/decay time at zero bias is 0.3/0.25 s. Therefore, the enhanced device performance strongly suggests the great potential of such a trilayer heterojunction device for use in high-performance perovskite photodetectors.

All-solution-processed UV-IR broadband trilayer photodetectors with CsPbBr3 colloidal nanocrystals as carriers-extracting layer.

Colloidal quantum dots (CQDs) are very promising nanomaterials for optoelectronics due to their tunable bandgap and quantum confinement effect. All-inorganic CsPbX3 (X = Br, Cl and I) perovskite nanocrystals (NCs) have attracted enormous interests owing to their promising and exciting applications in photovoltaic devices. In this paper, all-solution-processed UV-IR broadband trilayer photodetectors ITO/ZnO/PbS/CsPbBr3/Au and ITO/ZnO/CsPbBr3/PbS/Au with high performance were presented. The role of CsPbBr3 QDs layer as the carriers-extracting layer in the trilayer devices was discussed. As compared with bilayer device ITO/ZnO/PbS/Au, both the dark currents and photocurrents under illumination from trilayer photodetectors are enhanced, but the trilayer photodetector ITO/ZnO(80 nm)/PbS(150 nm)/CsPbBr3(50 nm)/Au showed a maximum specific detectivity (D*) of 8.3 × 1012 Jones with a responsivity (R) of 35 A W-1 under 1.6 mW cm-2 980 nm illumination. However, another trilayer photodetector ITO/ZnO(80 nm)/CsPbBr3(50 nm)/PbS(150 nm)/Au showed a maximum D* of 1.73 × 1012 Jones with a R of 5.31 A W-1 under 6.8 mW cm-2 405 nm illumination. Further, the underlying mechanism for the enhanced performance of trilayer photodetectors was discussed. Thus, this strategy of all-solution-processed heterojunction configuration paves a facile way for broadband photodetectors with high performance.

Ultra-sensitive solution-processed broadband photodetectors based on vertical field-effect transistor.

In the past few decades, great attention has been paid to the development of IV-VI semiconductor colloidal quantum dots, such as PbSe, PbS and PbSSe, in infrared (IR) photodetectors due to their high photosensitivity, solution-processing and low cost fabrication. IR photodetectors based on field-effect transistors (FETs) showed high detectivity since the transconductance can magnify the drain-source current under certain applied gate voltages. However, traditional lateral FETs usually suffer from low photosensitivity and slow responsivity, which restricts their widespread commercial applications. In this work, therefore, novel vertical FET (VFET) based photodetectors are presented, in which the active layer is sandwiched between porous source electrode and planar drain electrode, resulting to ultrashort channel length. In this way, enhanced photoresponsivity and specific detectivity of 291 A W-1 and 1.84 × 1014 Jones, respectively, can be obtained at low drain-source voltage (V DS) of -1 V and gate voltage (V g) of -2 V under 100 µW cm-2 illumination intensity, which was better than that of the traditional lateral FET based photodetectors. Therefore, it is promising to fabricate broadband photodetectors with high performance and good stability by this easy approach.

High-performance solution-processed colloidal quantum dots-based tandem broadband photodetectors with dielectric interlayer.

Recently, great attention has been paid to IV-VI colloidal quantum dots (CQDs) for their high photosensitivity, solution processability and low cost. Also, metal halide perovskites are very promising materials to realize the high-performance solution-processed visible-light photodetectors due to their cost-effective manufacturing, tunable absorption and photoluminescence in whole visible spectrum. In this paper, we present solution-processed CQDs-based tandem broadband photodetectors with low dark-current and high-sensitivity by inserting dielectric Polymethyl methacrylate (PMMA) interlayer between two sub-detectors. Our experimental data showed that the tandem broadband photodetector ITO/PEDOT:PSS/CsPbBr3:PbS0.4Se0.6/ZnO/PVK/CsPbBr3:PbS0.4Se0.6/ZnO/Au showed a maximum specific detectivity of 6.8 × 1013 Jones with a responsivity of 27 A W-1 under 57.8 µW cm-2 980 nm illumination. The device performance can be further enhanced by inserting a 50 nm dielectric PMMA layer between the two sub-photodetectors. As the result, the tandem photodetector ITO/PEDOT:PSS/CsPbBr3:PbS0.4Se0.6/ZnO/PMMA(50 nm)/PVK/CsPbBr3:PbS0.4Se0.6/ZnO/Au exhibits a maximum specific detectivity of 1.32 × 1014 Jones with a responsivity of 27.72 A W-1 under 57.8 µW cm-2 of 980 nm laser. Further, the physical mechanisms for the enhanced performance are discussed in detail.

Solution-phase, template-free synthesis of PbI2 and MAPbI3 nano/microtubes for high-sensitivity photodetectors.

Organic-inorganic hybrid perovskite materials with exotic semiconducting properties have become inevitable candidates for next-generation electronic devices. Very recently, a low dimensional nanostructure of the perovskite materials has attracted the scientific community due to its enhanced performance in optoelectronics as compared to its bulk counterparts. Herein, a facile method was developed for the scalable, room-temperature synthesis of CH3NH3PbI3 (MAPbI3) nano/microtubes by direct conversion of lead iodide (PbI2) microtubes through a solution-phase method. At first, the PbI2 microtubes were synthesized by the anti-solvent crystallization process and subsequently converted to CH3NH3PbI3 nano/microtubes by the addition of CH3NH3I (MAI) precursor directly in the solution phase. The corresponding photodetectors (PDs) in the lateral metal-semiconductor-metal (MSM) configuration of the PbI2 microtubes and MAPbI3 nano/microtubes on glass substrates were investigated systematically. Compared to the PbI2 based PDs (557 mA W-1, 3.65 × 1012 Jones, 0.251 s/0.252 s), the MAPbI3 based PDs exhibit higher photoresponsivity, specific detectivity, and faster response time (25 A W-1, 9.9 × 1013 Jones, 49 ms/20 ms) under irradiation with 4.6 µW cm-2 intensity light of the 532 nm laser at a bias of 5 V. The proposed method is a low-temperature process, easy to apply in large scale synthesis, and finds potential applications in optoelectronic devices.

A one-step method to synthesize CH3NH3PbI3:MoS2 nanohybrids for high-performance solution-processed photodetectors in the visible region.

A facile method to synthesize a CH3NH3PbI3: MoS2 nanohybrid for high-performance solution-processed photodetectors is presented. The interfacial charge carriers transfer due to the existence of heterojunctions between the 2D MoS2 nanosheet and perovskite cuboids are utilized to enhance the device performance. The dark current of the photodiode Au/CH3NH3PbI3: MoS2/Au was suppressed and its photocurrent was enhanced when compared to a pristine perovskite nanocrystal device Au/CH3NH3PbI3/Au. The lowest dark current of 0.34 × 10-9 A was observed from the photodiode Au/CH3NH3PbI3: MoS2/Au and the photoresponsivity and photosensitivity increased from 312 mA W-1 to 696 mA W-1 and from 9.02 to 87.47, respectively, showing an enhancement of 123.1% and 869.7%. Also, the rising time and falling time were reduced from 73 ms to 50 ms and 60 ms to 16 ms, respectively, when compared to those for the pristine perovskite nanocrystal-based photodiode Au/CH3NH3PbI3/Au. Therefore, this method provides a simple and effective approach to synthesize 2D nanosheet blended organic-inorganic nanohybrids for application in optoelectronic devices.

The outcomes of pars plana vitrectomy without endotamponade for tractional retinal detachment secondary to proliferative diabetic retinopathy.

AIM: To evaluate the outcomes of pars plana vitrectomy (PPV) without the use of an ocular tamponade in patients having tractional retinal detachment (TRD) secondary to proliferative diabetic retinopathy (PDR). METHODS: It was an interventional study conducted at the Department of Ophthalmology, B.V. Hospital, Bahawalpur, Pakistan, from July 2011 to July 2012. A total of 75 patients (84 eyes) having TRD secondary to PDR were treated by PPV without using an ocular tamponade. All patients included in the study had a tractional retinal detachment secondary to proliferative diabetic retinopathy but didn't have or develop retinal breaks before or during the study period. The surgical procedure included a PPV combined with the removal of the tractional retinal membranes and the application of endolaser photocoagulation to the retina. The mean follow-up period was 12 months. RESULTS: Successful retinal reattachement was observed in 78 of the operated eyes (92.8%). In these patients, the retina remained attached till the end of the one year follow-up period. Improvement in best corrected visual acuity (BCVA) was seen in 63 eyes (75%). The visual acuity remained unchanged in 9 eyes (10.7%). Mean improvement in BCVA was 2.00+1.24 at baseline to 1.24+1.22 (P<0.05) at the end of the follow-up period. CONCLUSION: In the absence of the retinal breaks, a TRD secondary to PDR can be successfully treated by pars plana vitrectomy without the use of an ocular tamponade.

The Outcomes of Pars Plana Vitrectomy without Tamponade for Tractional Retinal Detachment Secondary to Diabetic Retinopathy.

BACKGROUND: The objective of this research was to evaluate the outcomes of pars plana vitrectomy (PPV) without the use of an ocular tamponade in patients with tractional retinal detachment (TRD) secondary to proliferative diabetic retinopathy (PDR) presenting to Bahawal Victoria Hospital, Bahawalpur, Pakistan. METHODS: This was an interventional study conducted at the Department of Ophthalmology, Bahawal Victoria (B.V.) Hospital, Bahawalpur, Pakistan, from July 2011 to July 2012. A total of 75 patients (84 eyes) with TRD secondary to PDR were treated by PPV without using an ocular tamponade. All patients included in the study had a TRD secondary to PDR but did not have or develop retinal breaks before or during the study period. The surgical procedure included a PPV combined with the removal of the tractional retinal membranes and the application of endolaser photocoagulation to the retina. The mean follow-up period was 12 months. RESULTS: The study included 75 patients (84 eyes). Among these, 40 patients were females and 35 males. Successful retinal reattachment was observed in 78 of the operated eyes (92.8%). In these patients, the retina remained attached until the end of the 12 month follow-up period. Improvement in best corrected visual acuity (BCVA) was seen in 63 eyes (75%). The visual acuity remained unchanged in nine eyes (10.7%). Mean improvement in BCVA was 2.00 ± 1.24 at baseline to 1.24 ± 1.22 (P = 0.010) at the end of the follow-up period. CONCLUSION: In the absence of retinal breaks, a TRD secondary to PDR can be successfully treated and improved by PPV without the use of an ocular tamponade.

Comparison of the efficacy between an intravitreal and a posterior subtenon injection of triamcinolone acetonide for the treatment of diffuse diabetic macular edema.

OBJECTIVE: To compare the efficacy of an intravitreal injection to a posterior subtenon injection of triamcinolone acetonide for the treatment of diffuse diabetic macular edema. MATERIALS AND METHODS: Sixty patients with diabetes mellitus presenting with diffuse diabetic macular edema were recruited for the study. In each patient, one eye received a 4.0 mg (0.1 mL) intravitreal (IVT) injection of TA and the other eye was treated with a 40 mg (1.0 mL) posterior subtenon (PST) injection of triamcinolone acetonide (TA). We measured the visual acuity, the intraocular pressure (IOP) and the thickness of the macula using optical coherence tomography (OCT) before treatment and at one, three and six months after treatment. RESULTS: Eyes treated with PST showed 1-3 lines of improvement in Snellen's acuity from their pre-injection baseline visual status. The eyes in the IVT group showed 1-3 lines of improvement in Snellen's acuity in 80% of the treated eyes, but 20% of the treated eyes did not display any benefit at the end of six months. The difference in acuity between an IVT injection and a PST injection at six months post-treatment was statistically significant (p<0.05). The macular thickness of the eyes treated with an IVT injection was significantly reduced after one (222.7±13.4 µm; p<0.001) and three months (228.1±10.6 µm; p<0.001) of treatment. The eyes treated with a PST injection displayed a slow response and a significant improvement in macular thickness that was observed only after three months (231.3±10.9 µm; p<0.001). The difference between the eyes treated with an IVT injection (385.2±11.3 µm) and those treated with a PST injection (235.4±8.7 µm) was significantly different six months after treatment (p<0.001). The IOP of the eyes treated with an IVT injection was significantly increased after one (17.7±1.1 mm/Hg; p<0.020), three (18.2±1.2 mm/Hg; p<0.003) and six months (18.1±1.320 mm/Hg; p<0.007) when compared to the baseline value (16.1±1.4 mm/Hg). The eyes treated with a PST injection displayed no significant increase in IOP after one (16.4±1.2 mm/Hg; p<0.450), three (16.3±1.1 mm/Hg; p<0.630) and six months (16.2±1.1 mm/Hg; p<0.720) when compared to the baseline value (16.2±1.3 mm/Hg). CONCLUSION: A PST injection is equally effective and safer than an IVT injection of TA for the management of diffuse DME.