Solution-processed Semiconductors Research Articles

Solution-processed wafer-scale indium selenide semiconductor thin films with high mobilities

Solution-processed wafer-scale indium selenide semiconductor thin films with high mobilities

Low-threshold anisotropic polychromatic emission from monodisperse quantum dots.

Colloidal quantum dots (QDs) are solution-processable semiconductor nanocrystals with favorable optoelectronic characteristics, one of which is their multi-excitonic behavior that enables broadband polychromatic light generation and amplification from monodisperse QDs. However, the practicality of this has been limited by the difficulty in achieving spatial separation and patterning of different colors as well as the high pumping intensity required to excite the multi-excitonic states. Here, we have addressed these issues by integrating monodisperse QDs in multi-excitonic states into a specially designed cavity, in which the QDs exhibit an anisotropic polychromatic emission (APE) characteristic that allows for tuning the emission from green to red by shifting the observation direction from perpendicular to lateral. Subsequently, the APE threshold under 300-ps pulsed excitation has been reduced from 32 to 21μJ cm-2 by optimizing the cavity structure. Based on the manipulation of multi-excitonic emission and angle-dependent wavelength selectivity of the developed cavity, we have fabricated a full-color micro-pixel array with a pixel size as small as 23μm by combining cavity-integrated monodisperse QDs and blue backlight. Furthermore, the threshold of APE under quasi-continuous-wave pumping was as low as 5W cm-2, indicating its compatibility with commercial LEDs and/or laser diodes. Since APE arises from the multi-excitonic behavior of QDs that supports optical gain, its unprecedentedly low threshold suggests the feasibility of the diode-pumped colloidal QD laser. This work demonstrates a novel method of manipulating the QDs' optical properties beyond controlling their size, composition or structure, and reveals great potential for achieving full-color emission using monodisperse QDs.

Continuous-wave perovskite polariton lasers.

Solution-processed semiconductor lasers are next-generation light sources for large-scale, bio-compatible and integrated photonics. However, overcoming their performance-cost trade-off to rival III-V laser functionalities is a long-standing challenge. Here, we demonstrate room-temperature continuous-wave perovskite polariton lasers exhibiting remarkably low thresholds of ~0.4 W cm-2, enabled by a variable single-crystal perovskite microcavity. The threshold outperforms state-of-the-art III-V lasers by ~30 times under optical pumping, and is exceptional among solution-processed lasers. The ultralow-threshold lasing arises from steady-state exciton-polariton condensation, a macroscopic quantum phenomenon akin to Bose-Einstein condensation. The steady-state condensation is attained by fine-tuning the cavity photon-exciton energy separation near the degeneracy point for strong light-matter interactions. These mechanisms enabled the initial demonstration of an indirectly injected perovskite laser chip powered by a gallium nitride light-emitting diode. Our findings create exciting avenues toward on-chip integration of solution-processed lasers, opening opportunities for lasing with ultralow energy consumption and unprecedented performance.

Colloidal semiconductor quantum shells for solution-processed laser applications.

Laser diodes based on solution-processed semiconductor quantum dots (QDs) present an economical and color-tunable alternative to traditional epitaxial lasers. However, their efficiency is significantly limited by non-radiative Auger recombination, a process that increases lasing thresholds and diminishes device longevity through excessive heat generation. Recent advancements indicate that these limitations can be mitigated by employing spherical quantum wells, or quantum shells (QSs), in place of conventional QDs. The unique QS geometry is designed to suppress multi-exciton Auger decay through exciton-exciton repulsion, thereby extending multi-exciton lifetimes and enhancing their radiative recombination efficiency. In this review, we examine optoelectronic characteristics of QSs and discuss their integration into photonic laser cavities. We further present experimental data demonstrating QS performance in femtosecond, quasi-continuous-wave (quasi-CW), and two-photon upconverted laser configurations, underscoring QS capability to achieve efficient lasing with reduced thresholds and lower energy losses.

The Influence of Nickel Doping on the Metal-Oxide in Solution-Processed Transistors Based on Indium Zinc Oxide

Solution-processing of nickel zinc oxide (IZO) thin-film transistors (TFTs) is gaining traction as a cornerstone of future display technology, promising cost-effective production. However, achieving stability in the off-current state of IZO without using Ga, a less eco-friendly dopant, remains a challenge. This study proposes a solution-based doping method for IZO semiconductors employing a Ni carrier suppressor and examines the impact of Ni on transistor operation. By leveraging the similar size of Ni2+ to Zn2+, an optimal Ni concentration selectively substitutes Zn sites, leading to a reduction in hydroxide groups bonded to Zn and enhancing the bonding strength of Ni with O. Conversely, excessive Ni addition impedes the formation of a smooth thin film. Ni-doped IZO TFT devices with optimized Ni concentrations exhibit superior performance, characterized by significantly lower off-state currents while maintaining high on-state currents compared to conventional IZO TFTs. This approach expands the repertoire of solution-processed metal oxide semiconductors, offering a sustainable alternative for carrier suppression and facilitating the cost-effective and straightforward fabrication of TFTs.

Engineered Catalyst Patterns on Hematite Photoanodes for Improved Photoelectrochemical Water Oxidation Efficiency

The heavy dependence on fossil fuels is a major contributor to global warming, creating an urgent need for a swift transition to renewable energy sources like solar irradiation. Photoelectrochemical (PEC) cells present a promising method for converting solar energy into chemical fuels. However, the current efficiency of PECs is inadequate for large-scale commercialization. One key obstacle to improving PEC efficiency lies in the complex and inefficient processes, from photon absorption by semiconductors to the selective transfer of photogenerated charges to redox species in the electrolyte. This study proposes a novel approach to boost PEC performance by utilizing three-dimensionally patterned catalysts on solution-processed metal oxide semiconductors, focusing on optimizing the crucial electrolyte | catalyst | semiconductor interface. By applying patterned cobalt-based catalysts onto hematite (α-Fe2O3) nanorods through a photomask-free, light-guided electrodeposition technique, we achieve direct control over the catalyst's location and distribution on the photoelectrode without relying on photolithography. The resulting electrolyte | patterned catalyst | α−Fe2O3 interface not only ensures sufficient light absorption in the front-illumination setup but also enhances the transport and transfer of photogenerated holes across the interface, reducing carrier recombination and minimizing parasitic light absorption and scattering by the catalytic layers. We confirm that electrodeposition on hematite does not affect the semiconductor's energy profile, including key parameters such as flat-band potential, carrier density, and band structure. The improved performance in PEC water oxidation is primarily due to the increased light absorption achieved by our patterned catalyst | α−Fe2O3 photoelectrode, as demonstrated by UV-Vis spectroscopy absorbance data.

Performance enhancement of solution-processed organic thin-film transistors incorporating an improved Corbino structure

The solution-processed organic thin-film transistors (OTFTs) with a minimal device footprint and improved performance are desirable for flexible electronics and other circuit applications. It is demonstrated that the enhanced performance can be achieved for solution-processed OTFTs by adopting an improved Corbino structure. The bottom-gate bottom-contact OTFTs of W/L ratio of 500 are fabricated using the standard poly-3-hexylthiophene (P3HT) as a semiconductor with an improved interdigitated pseudo-Corbino (IPC) structure. The exhibited IPC structure is a combination of interdigitated structure in the enclosed-Corbino design to achieve infinite output resistance, suppressed parasitic leakage current, and high ON current by accommodating a high W/L ratio in a minimal device footprint. For the fabricated solution-processed OTFTs, infinite output resistance with an OFF-current of the order of 10−12 A and an ON/OFF ratio of drain current of the order of 107 is achieved. Incorporating an enhanced hexamethyldisilazane treatment of the SiO2 gate dielectric improves the ON/OFF ratio to a record value of 108 and the mobility of the order of 10−2 cm2/Vs for P3HT. Implementation of IPC-TFT structure for intentionally chosen moderate-mobility, solution-processed P3HT semiconductor results in a consistent low OFF-current, high ON/OFF ratio, and infinite output resistance with excellent device-to-device uniformity.

Optical Applications of CuInSe2 Colloidal Quantum Dots.

The distinctive chemical, physical, electrical, and optical properties of semiconductor quantum dots (QDs) make them a highly fascinating nanomaterial that has been extensively studied. The CuInSe2 (CIS) QDs demonstrates great potential as a nontoxic alternative to CdSe and PbSe QDs for realizing high-performance solution-processed semiconductor devices. The CIS QDs show strong light absorption and bright emission across the visible and infrared spectrum and have been designed to exhibit optical gain. The special characteristics of these properties are of great significance in the fields of solar energy conversion, display, and electronic devices. Here, we present a comprehensive overview of the potential applications of colloidal CIS QDs in various fields, with a particular focus on solar energy conversion (such as QD solar cells, QD-sensitized solar cells, and QD luminescence solar concentrators), solar-to-hydrogen production (such as photocatalytic and photoelectrochemical H2 production), and QD electronics (such as QD transistors, QD light-emitting diodes, and QD photodetectors). Furthermore, we offer our insights into the current challenges and future opportunities associated with CIS QDs for further research.

Solution-processable ordered defect compound semiconductors for high-performance electronics.

Solution-processable semiconductors hold promise in enabling applications requiring cost-effective electronics at scale but suffer from low performance limited by defects. We show that ordered defect compound semiconductor CuIn5Se8, which forms regular defect complexes with defect-pair compensation, can simultaneously achieve high performance and solution processability. CuIn5Se8 transistors exhibit defect-tolerant, band-like transport supplying an output current above 35 microamperes per micrometer, with a large on/off ratio greater than 106, a small subthreshold swing of 189 ± 21 millivolts per decade, and a high field-effect mobility of 58 ± 10 square centimeters per volt per second, with excellent uniformity and stability, superior to devices built on its less defective parent compound CuInSe2, analogous binary compound In2Se3, and other solution-deposited semiconductors. They can be monolithically integrated with carbon nanotube transistors to form high-speed and low-voltage three-dimensional complementary logic circuits and with micro-light-emitting diodes to realize high-resolution displays.

Silver Telluride Colloidal Quantum Dot Solid for Fast Extended Shortwave Infrared Photodetector.

Extended shortwave infrared (eSWIR) photodetectors that employ solution-processable semiconductors have attracted attention for use in applications such as ranging, night vision, and gas detection. Colloidal quantum dots (CQDs) are promising materials with facile bandgap tunability across the visible-to-mid-infrared wavelengths. However, toxic elements, such as Hg and Pb, and the slow response time of CQD-based IR photodetectors, limit their commercial viability. This article presents a novel eSWIR photodetector that is fabricated using silver telluride (Ag2Te) CQDs. Effective thiolate ligand exchange enables a lower trap density and improved carrier mobility in CQD solids. Furthermore, a vertical p-n photodiode architecture with a favorable energy-level landscape is utilized to facilitate charge extraction, resulting in a fast, room-temperature-operable, and toxic-element-free CQD photodetector. The best eSWIR Ag2Te CQD photodetector exhibits a fall time of 72ns, representing the fastest response time among all prior CQD-based eSWIR photodetectors, including those containing toxic elements, such as Pb and Hg.

Inkjet-printed p-type tellurene and n-type MoS2 transistors for CMOS electronics

Abstract Two-dimensional semiconductor materials combine exceptional electronic transport properties with mechanical flexibility and hence can be an ideal choice for large-area flexible and wearable electronics. While inkjet printing may be a suitable approach to fabricate high throughput electronic components on polymer substrates, solution-processed 2D semiconductor network transistors suffer from two major hindrances: extremely high inter-flake resistance and the lack of high-performance p-type semiconductors. This study shows that inkjet-printed tellurium nanowires or tellurene nanoflakes can offer high-performance p-type TFTs with current density up to 100 μA/μm and an On-Off ratio >105. In order to circumvent the high inter-flake junction resistance, a narrow-channel, near-vertical device architecture has been used that ensures predominantly intra-flake/ intra-nanowire transport, which resulted in three orders of magnitude increase in the current density compared to conventional devices without compromising on the On-Off ratio. Moreover, we show the whole device operation within ± 2 V, with a threshold voltage close to 0 V. The complete device fabrication is carried out at room temperature, thereby making it compatible with inexpensive polymer substrates. Next, outstanding device performance has also been realized with electrochemically-exfoliated and inkjet-printed n-type MoS2 TFTs, demonstrating a current density of 60 μA/μm and an On-Off ratio of 106. Furthermore, we show tellurene-based p-type depletion-load unipolar inverters and CMOS inverters alongside n-type MoS2 TFTs, demonstrating a signal gain of 12 and 11, respectively. The CMOS inverters are found to operate at a frequency of 1 kHz.

Enhanced electrical performance and stability of solution-processed oxide semiconductor thin-film transistors via an incorporation of deionized water oxidizer

Solution-processed amorphous oxide semiconductor thin films contain poor metal-oxygen-metal (M-O-M) networks and numerous impurities, making it difficult to manufacture high-performance semiconductor devices with excellent stability. In this study, we enhance the electrical performance and device stability of solution-processed oxide thin-film transistors (TFTs) by incorporating water molecular oxidants. In solution, a water molecule can be easily incorporated by adding deionized water (DW) to the precursor solution. The DW-incorporated precursor solutions induced the production of oxide semiconductor thin films with improved M-O-M networks and fewer defect states. Therefore, compared to conventional case, the DW-incorporated indium zinc oxide (InZnO) TFT showed improved device performances and significantly reduced changes of threshold voltage under positive gate bias stress and negative gate bias/illumination stress conditions. This approach of incorporating DW into the precursor solutions provides a promising route for fabricating high-quality amorphous semiconductor films and transistor devices.

A library of 2D electronic material inks synthesized by liquid-metal-assisted intercalation of crystal powders

Solution-processable 2D semiconductor inks based on electrochemical molecular intercalation and exfoliation of bulk layered crystals using organic cations has offered an alternative pathway to low-cost fabrication of large-area flexible and wearable electronic devices. However, the growth of large-piece bulk crystals as starting material relies on costly and prolonged high-temperature process, representing a critical roadblock towards practical and large-scale applications. Here we report a general liquid-metal-assisted approach that enables the electrochemical molecular intercalation of low-cost and readily available crystal powders. The resulted solution-processable MoS2 nanosheets are of comparable quality to those exfoliated from bulk crystals. Furthermore, this method can create a rich library of functional 2D electronic inks ( >50 types), including 2D wide-bandgap semiconductors of low electrical conductivity. Lastly, we demonstrated the all-solution-processable integration of 2D semiconductors with 2D conductors and 2D dielectrics for the fabrication of large-area thin-film transistors and memristors at a greatly reduced cost.

Spin coating on a budget: A 3D-Printed all-mechanical alternative for cost-effective thin-film deposition

Spin coating stands out as the most employed thin-film deposition technique across a variety of scientific fields. Particularly in the past two decades, spin coaters have become increasingly popular due to the emergence of solution-processed semiconductors such as quantum dots and perovskites. However, acquiring commercial spin coaters from reputable suppliers remains a significant financial burden for many laboratories, particularly for smaller research or educational facilities. Prompted by the simple mechanical principles of the device, in this work, we present a 3D-printed analogue that can be printed and assembled in under 10 h and costs less than 5 euros per device. The operating principle is fully mechanical since the rotating motion is induced by gas flow. It does not require any additional components such as DC motors, motor drivers, circuitry or software and thus it can be fully operational off the grid. Additionally, the gas flow generates a purging effect that was found to be rather advantageous for film formation. To prove the effectiveness of this device, we have employed it to fabricate planar thin-film antimony sulfide (Sb2S3) solar cells. The optoelectronic characteristics of solar cells revealed noteworthy improvements, particularly in terms of repeatability, when compared to those fabricated with a commercial spin coater.

Modulating the Structure and Optoelectronic Properties of Solution-Processed Bismuth-Based Nanocrystals.

Bismuth-based chalcogenides have emerged as promising candidates for next-generation, solution-processable semiconductors, mainly benefiting from their facile fabrication, low cost, excellent stability, and tunable optoelectronic properties. Particularly, the recently developed AgBiS2 solar cells have shown striking power conversion efficiencies. High performance bismuth-based photodetectors have also been extensively studied in the past few years. However, the fundamental properties of these Bi-based semiconductors have not been sufficiently investigated, which is crucial for further improving the device performance. Here, we introduce multiple time-resolved and steady-state techniques to fully characterize the charge carrier dynamics and charge transport of solution-processed Bi-based nanocrystals. It was found that the Ag-Bi ratio plays a critical role in charge transport. For Ag-deficient samples, silver bismuth sulfide thin films behave as localized state induced hopping charge transport, and the Ag-excess samples present band-like charge transport. This finding is crucial for developing more efficient Bi-based semiconductors and optoelectronic devices.

Perovskite/organic tandem device to realize light detection and emission dual function

Developing highly integrated smart optoelectronic systems is vital to modern technology, yet critically challenging. This study introduces a tandem device that incorporates an organic photodiode (OPD) and a perovskite light emitting diode (PeLED), enabling simultaneous light detection and emission in one compact device, prepared by all-solution fabrication process. It shows that precise control of interfacial properties plays a critical role in establishing the all-solution processed OPD/PeLED multi-layered dual-function device which is critical for charge transport, recombination, and generation. The integrated structure allows for light detection and emission function selectively by controlling the polarity of the external bias. The optoelectronic performance of the dual-function tandem device is comparable to that of the discrete control OPD and PeLED, i.e., the tandem device achieves a responsivity of 94 mA/W at 850 nm under −1 V and a luminance result of 1319 cd/m2 at 516 nm under 7 V, which is comparable to 101 mA/W and 1983 cd/m2 for the control OPD and PeLED operated under the same conditions. This work demonstrates the promising properties of the monolithically integrated dual-functional device and its potential for application in health monitoring and wearable electronic devices.

Understanding Antiferromagnetic Coupling in Lead-Free Halide Double Perovskite Semiconductors.

Solution-processable semiconductors with antiferromagnetic (AFM) order are attractive for future spintronics and information storage technology. Halide perovskites containing magnetic ions have emerged as multifunctional materials, demonstrating a cross-link between structural, optical, electrical, and magnetic properties. However, stable optoelectronic halide perovskites that are antiferromagnetic remain sparse, and the critical design rules to optimize magnetic coupling still must be developed. Here, we combine the complementary magnetometry and electron-spin-resonance experiments, together with first-principles calculations to study the antiferromagnetic coupling in stable Cs2(Ag:Na)FeCl6 bulk semiconductor alloys grown by the hydrothermal method. We show the importance of nonmagnetic monovalence ions at the BI site (Na/Ag) in facilitating the superexchange interaction via orbital hybridization, offering the tunability of the Curie-Weiss parameters between -27 and -210 K, with a potential to promote magnetic frustration via alloying the nonmagnetic BI site (Ag:Na ratio). Combining our experimental evidence with first-principles calculations, we draw a cohesive picture of the material design for B-site-ordered antiferromagnetic halide double perovskites.

Observation of Ferromagnetism in Dilute Magnetic Halide Perovskite Semiconductors.

Dilute magnetic semiconductors (DMSs) have attracted much attention because of their potential use in spintronic devices. Here, we demonstrate the observation of robust ferromagnetism in a solution-processable halide perovskite semiconductor with dilute magnetic ions. By codoping of magnetic (Fe2+) and aliovalent (Bi3+) metal ions into CH3NH3PbCl3 (MAPbCl3) perovskite, ferromagnetism with well-saturated magnetic hysteresis loops and a maximum coercivity field of 1280 Oe was observed below 12 K. The ferromagnetic resonance measurements revealed that the incorporation of aliovalent ions modulates the carrier concentration and plays an essential role in realizing the ferromagnetism in dilute magnetic halide perovskites. Magnetic ions are proposed to interact through itinerant charge carriers to achieve ferromagnetic coupling. Our work provides a new avenue for the development of solution-processable magnetic semiconductors.

Colloidal InAs Quantum Dot-Based Infrared Optoelectronics Enabled by Universal Dual-Ligand Passivation.

Solution-processed low-bandgap semiconductors are crucial to next-generation infrared (IR) detection for various applications, such as autonomous driving, virtual reality, recognitions, and quantum communications. In particular, III-V group colloidal quantum dots (CQDs) are interesting as nontoxic bandgap-tunable materials and suitable for IR absorbers; however, the device performance is still lower than that of Pb-based devices. Herein, a universal surface-passivation method of InAs CQDs enabled by intermediate phase transfer (IPT), a preliminary process that exchanges native ligands with aromatic ligands on the CQD surface is presented. IPT yields highly stable CQD ink. In particular, desirable surface ligands with various reactivities can be obtained by dispersing them in green solvents. Furthermore, CQD near-infrared (NIR) photodetectors are demonstrated using solution processes. Careful surface ligand control via IPT is revealed that enables the modulation of surface-mediated photomultiplication, resulting in a notable gain control up to ≈10 with a fast rise/fall response time (≈12/36ns). Considering the figure of merit (FOM), EQE versus response time (or -3dB bandwidth), the optimal CQD photodiode yields one of the highest FOMs among all previously reported solution-processed nontoxic semiconductors comprising organics, perovskites, and CQDs in the NIR wavelength range.

Supramolecular assembly of blue and green halide perovskites with near-unity photoluminescence.

The metal-halide ionic octahedron is the optoelectronic unit for halide perovskites, and a crown ether-assisted supramolecular assembly approach can pack various ionic octahedra into tunable symmetries. In this work, we demonstrate near-unity photoluminescence quantum yield (PLQY) blue and green emission with the supramolecular assembly of hafnium (Hf) and zirconium (Zr) halide octahedral clusters. (18C6@K)2HfBr6 powders showed blue emission with a near-unity PLQY (96.2%), and green emission was also achieved with (18C6@K)2ZrCl4Br2 powders at a PLQY of 82.7%. These highly emissive powders feature facile low-temperature solution-based synthesis conditions and maintain high PLQY in solution-processable semiconductor inks under ambient conditions, and they were used in thin-film displays and emissive three-dimensional-printed architectures that exhibited high spatial resolution.