Heavy-Metal-Free Flexible Hybrid Polymer-Nanocrystal Photodetectors Sensitive to 1.5 μm Wavelength

Advances in Flexible Organic Photodetectors: Materials and Applications

Future electronics will need to be mechanically flexible and stretchable in order to enable the development of lightweight and conformal applications. In contrast, photodetectors, an integral component of electronic devices, remain rigid, which prevents their integration into everyday life applications. In recent years, significant efforts have been made to overcome the limitations of conventional rigid photodetectors, particularly their low mechanical deformability. One of the most promising routes toward facilitating the fabrication of flexible photodetectors is to replace conventional optoelectronic materials with nanomaterials or organic materials that are intrinsically flexible. Compared with other functional materials, organic polymers and molecules have attracted more attention for photodetection applications due to their excellent photodetection performance, cost-effective solution-fabrication capability, flexible design, and adaptable manufacturing processes. This article comprehensively discusses recent advances in flexible organic photodetectors in terms of optoelectronic, mechanical properties, and hybridization with other material classes. Furthermore, flexible organic photodetector applications in health-monitoring sensors, X-ray detection, and imager devices have been surveyed.

Colloidal upconversion nanocrystals enable low-temperature-grown GaAs photoconductive switch operating atλ = 1.55μm

Microwave photoconductive switches, allowing an optical control on the magnitude and phase of the microwave signals to be transmitted, are important components for many optoelectronic applications. In recent years, there are significant demands to develop photoconductive switches functional in the short-wave-infrared spectrum window (e.g.λ = 1.3-1.55μm) but most state-of-the-art semiconductors for photoconductive switches cannot achieve this goal. In this work, we propose a novel approach, by the use of solution-processed colloidal upconversion nanocrystals deposited directly onto low-temperature-grown gallium arsenide (LT-GaAs), to achieve microwave photoconductive switches functional atλ = 1.55μm illumination. Hybrid upconversion Er³⁺-doped NaYF₄nanocrystal/LT-GaAs photoconductive switch was fabricated. Under a continuous waveλ = 1.55μm laser illumination (power density ∼ 12.9 mWμm^-2), thanks to the upconversion energy transfer from the nanocrystals, a more than 2-fold larger value in decibel was measured for the ON/OFF ratio on the hybrid nanocrystal/LT-GaAs device by comparison to the control device without upconversion nanoparticles. A maximum ON/OFF ratio reaching 20.6 dB was measured on the nanocrystal/LT-GaAs hybrid device at an input signal frequency of 20 MHz.

Upconversion nanoparticles extending the spectral sensitivity of silicon photodetectors to λ = 1.5 μm

The telecommunication wavelength of λ = 1.5 μm has been playing an important role in various fields. In particular, performing photodetection at this wavelength is challenging, demanding more performance stability and lower manufacturing cost. In this work, upconversion nanoparticle (UCNP)/Si hybrid photodetectors (hybrid PDs) are presented, made by integrating solution-processed Er³⁺-doped NaYF₄ upconversion nanoparticles (UCNPs) onto a silicon photodetector. After optimization, we demonstrated that a layer of UCNPs can well lead to an effective spectral sensitivity extension without sacrificing the photodetection performance of the Si photodetector in the visible and near-infrared (near-IR) spectrum. Under λ = 1.5 μm illumination, the hybrid UCNPs/Si-PD exhibits a room-temperature detectivity of 6.15 × 10¹² Jones and a response speed of 0.4 ms. These UCNPs/Si-PDs represent a promising hybrid strategy in the quest for low-cost and broadband photodetection that is sensitive in the spectrum from visible light down to the short-wave infrared.

Scalable Synthesis of a Sub-10 nm Chalcopyrite (CuFeS2) Nanocrystal by the Microwave-Assisted Synthesis Technique and Its Application in a Heavy-Metal-Free Broad-Band Photodetector

A heavy-metal-free chalcopyrite (CuFeS₂) nanocrystal has been synthesized via microwave-assisted growth. Large-scale nanocrystals with an average particle size of 5 nm are fabricated by this technique within a very short period of time without any need for organic ligands. Scanning electron microscopy study (SEM) of individual synthesis steps indicates that aggregates of nanocrystals are formed as flakes during microwave-assisted synthesis. The colloidal solution of the CuFeS₂ nanocrystal was prepared by sonicating these flakes. Transmission electron microscopy (TEM) study reveals the growth of sub-10 nm CuFeS₂ nanocrystals that are further characterized by X-ray diffraction. UV-visible absorption spectroscopic study shows that the band gap of this nanocrystal is ∼1.3 eV. To investigate the photosensitive nature of this nanocrystal, a bilayer p-n heterojunction photodetector has been fabricated using this nontoxic CuFeS₂ nanocrystal as a photoactive material and n-type ZnO as a charge-transport layer. The detectivity of this photodetector reaches above 10¹² Jones in visible and near-infrared (NIR) regions under 10 V external bias, which is significantly high for a nontoxic nanocrystal-based photodetector.

Solution Processed Hybrid Polymer: HgTe Quantum Dot Phototransistor with High Sensitivity and Fast Infrared Response up to 2400 nm at Room Temperature

Narrow bandgap semiconductor-based photodetectors often suffer from high room-temperature noise and are therefore operated at low temperatures. Here, a hybrid poly(3-hexylthiophene) (P3HT): HgTe quantum dot (QD) phototransistor is reported, which exhibits high sensitivity and fast photodetection up to 2400 nm wavelength range at room temperature. The active layer of the phototransistor consists of HgTe QDs well dispersed in a P3HT matrix. Fourier-transform infrared spectra confirm that chemical grafting between P3HT and HgTe QDs is realized after undergoing prolonged coblend stirring and a ligand exchange process. Thanks to the shifting of the charge transport into the P3HT and the partial passivation of the surface traps of HgTe QDs in the blend, the P3HT: HgTe QD hybrid phototransistor shows significantly improved gate-voltage tuning, 15 times faster response, and ≈80% reduction in the noise level compared to a pristine HgTe QD control device. More than 1011 Jones specific detectivity (estimated from the noise spectral density measured at 1 kHz) is achieved at room temperature, and the response time (measured at 22 mW cm-2 illumination intensity) of the device is less than 1.5 µs. That is comparable to commercial epitaxially grown IR photodetectors operated in the same wavelength range.