Mixed AgBiS2 nanocrystals for photovoltaics and photodetectors

Interplay between Cation "Coloring" and Stereochemically Active Lone Pairs in AgBiS2 Thin Films

Solution-processed AgBiS2 thin films were fabricated using novel thiol-amine precursor inks to investigate the stereochemical activity of Bi3+ 6s2 lone pairs and their impact on the structure. A dual-space analysis combining Bragg diffraction and hard X-ray photoelectron spectroscopy (HAXPES) revealed a rock salt-like average structure with local distortions linked to cation coloring. Density functional theory (DFT) and crystal orbital Hamilton population (COHP) analyses confirmed that local Bi-rich and Ag-rich nanodomains amplify stereochemical activity, whereas more mixed and cation-order nanodomains are less stereochemically active. This local, nanoscopic mixing of segregated and ordered domains would indeed explain an average Fm3̅m structure that is rock salt-like and that does not manifest the full anharmonicity and noncentrosymmetry evidenced in canonical structures with stereochemical expression. These findings provide insights into the local structural and electronic complexities governing the optoelectronic properties of AgBiS2 thin films.

Holistic Design of Charge Transfer Layers for Highly Efficient and Stable AgBiS2 Quantum Dot Photodetectors

Developing highly efficient and stable photodetectors based on eco-friendly AgBiS2 quantum dots (QDs) has garnered significant attention. However, optimizing charge transfer layers (CTLs) to enhance device performance and stability remains a critical challenge. Here, the study presents the development of highly efficient, stable, fully inorganic, self-powered AgBiS2 QD-based photodetectors through the holistic design of CTLs, consisting of zinc-copper-indium-sulfide QDs blended with black phosphorus nanosheets as hole-transport layers, and unzipped carbon nanotubes doped with ZnO nanoparticles as electron-transport layers. The rationally designed CTLs exhibit well-matched energy-level alignment with the AgBiS2 QDs layer and balanced charge mobility, resulting in a robust and efficient charge transfer system. The optimized device exhibits a responsivity of 20 mA/W and a detectivity of 1.9 × 1010 Jones at 1000 nm, among the best performance for heavy metal-free QD-based photodetectors. The all-inorganic nature of the devices demonstrates excellent stability for over 2 months in air, with minimal degradation in performance. Furthermore, these enhanced self-powered AgBiS2 QD-based photodetectors are used as light sensors in the receiver terminal of a near-infrared optical communication system. This work presents a comprehensive approach to the holistic design of CTLs in AgBiS2 QD-based photodetectors for achieving superior device performance and long-term stability.

Solution-Crystalized AgBiS2 Films for Solar Cells Generating a Photo-Current Density Over 31 mA cm-2

In response to the toxic heavy metal absorbers in perovskite solar cells (PSCs), this work focuses on the development of an environmentally friendly simple solution-processed infrared (IR) absorber. In this work, a simple solution-crystallized IR-absorbing AgBiS2 film is reported by spin-coating silver, bismuth nitrates, and thiourea dissolved in dimethylformamide (DMF) to produce thick AgBiS2 film. Extensive optimization of the precursor concentrations thicknesses and conductive substrates used allow for obtaining 250 nm AgBiS2 film with different crystal sizes. When applied as an absorber in solar cells, solution-crystalized AgBiS2 thick film delivers an extraordinarily high current density of over 31 mA cm-2. The devices show high stability under continuous 100 mW cm-2 illumination and when stored in the dark for more than six months. When the AgBiS2 layer is fabricated in a gradient fashion combining one layer of 0.25 m and three layers of 0.5 m precursor concentrations, the efficiency of 5.15% is registered which is the highest reported for the simple solution-crystallized AgBiS2 films.

Numerical Expedition on the Potential of AgBiS2-Based Thin Film Solar Cells Employing Different Carrier Transport Layers

In this study, a photovoltaic (PV) device has been developed by using AgBiS2 as the key material. The simulation of the photovoltaic cell has been performed using the SCAPS-1D simulator to analyze the impact of each layer. The design incorporates three window layers, CdS, In2S3, and ZnSe, alongside six familiar compounds, AlSb, CuGaSe2 (CGS), CuS, MoS2, Sb2S3, and WSe2, as the back surface field (BSF) layers. These heterostructures aim to uncover the potential of AgBiS2 in the realm of photovoltaic technology. When AgBiS2 functions within a singular heterojunction, specifically in configurations such as n-CdS/p-AgBiS2, n-In2S3/p-AgBiS2, and n-ZnSe/p-AgBiS2, the resulting values for open-circuit voltage (V OC) and the short circuit current (J SC) are found to be ∼0.90 V and ∼32 mA/cm2, respectively, while the corresponding power conversion efficiencies (PCE) are 23.56%, 22.60%, and 23.62%, respectively. On the contrary, the incorporation of various BSF layers like AlSb, CGS, CuS, MoS2, Sb2S3, and WSe2 results in a substantial increase in V OC, leading to an enhancement in PCE. Among the AgBiS2 based different dual-heterostructures, the outstanding PCE of 30.04% with a V OC of 1.12 V is achieved by n-ZnSe/p-AgBiS2/p+-Sb2S3 device. In comparison, the n-ZnSe/p-AgBiS2/p+-CGS structure exhibits a similar PCE of 30.03% with a V OC of 1.12 V. Additionally, the n-ZnSe/p-AgBiS2/p+-MoS2 arrangement demonstrates a PCE of 29.95% and a V OC of 1.12 V. The effective band alignments observed at the interfaces of ZnSe/AgBiS2 and AgBiS2/MoS2, ZnSe/AgBiS2 and AgBiS2/CGS, as well as ZnSe/AgBiS2 and AgBiS2/Sb2S3 contribute to a substantial built-in potential, leading to an elevated V OC. As an alternative to ZnSe, the CdS window could offer similar performances, whereas In2S3 might provide a lower efficiency. The elaborate simulation findings highlight the substantial potential of AgBiS2 as an absorber, particularly when coupled with different windows and BSF layers. This opens avenues for experimental research focused on AgBiS2 in the era of photovoltaic cells.

Fast Near-Infrared Photodetectors Based on Nontoxic and Solution-Processable AgBiS2

Solution-processable near-infrared (NIR) photodetectors are urgently needed for a wide range of next-generation electronics, including sensors, optical communications and bioimaging. However, it is rare to find photodetectors with >300 kHz cut-off frequencies, especially in the NIR region, and many of the emerging inorganic materials explored are comprised of toxic elements, such as lead. Herein, solution-processed AgBiS2 photodetectors with high cut-off frequencies under both white light (>1 MHz) and NIR (approaching 500 kHz) illumination are developed. These high cut-off frequencies are due to the short transit distances of charge-carriers in the ultrathin photoactive layer of AgBiS2 photodetectors, which arise from the strong light absorption of this material, such that film thicknesses well below 120 nm are sufficient to absorb >65% of NIR to visible light. It is also revealed that ion migration plays a critical role in the photo-response speed of these devices, and its detrimental effects can be mitigated by finely tuning the thickness of the photoactive layer, which is important for achieving low dark current densities as well. These outstanding characteristics enable the realization of air-stable, real-time heartbeat sensors based on NIR AgBiS2 photodetectors, which strongly motivates their future integration in high-throughput systems.

Cation exchange synthesis of AgBiS2 quantum dots for highly efficient solar cells

Silver bismuth sulfide (AgBiS2) nanocrystals have emerged as a promising eco-friendly, low-cost solar cell absorber material. Their direct synthesis often relies on the hot-injection method, requiring the application of high temperatures and vacuum for prolonged times. Here, we demonstrate an alternative synthetic approach via a cation exchange reaction. In the first-step, bis(stearoyl)sulfide is used as an air-stable sulfur precursor for the synthesis of small, monodisperse Ag2S nanocrystals at room-temperature. In a second step, bismuth cations are incorporated into the nanocrystal lattice to form ternary AgBiS2 nanocrystals, without altering their size and shape. When implemented into photovoltaic devices, AgBiS2 nanocrystals obtained by cation exchange reach power conversion efficiencies of up to 7.35%, demonstrating the efficacy of the new synthetic approach for the formation of high-quality, ternary semiconducting nanocrystals.

Carrier Dynamics of Efficient Triplet Harvesting in AgBiS2 /Pentacene Singlet Fission Solar Cells

Singlet fission is a process by which an organic semiconductor is able to generate two triplet excitons from a single photon. If charges from the triplets can be successfully harvested without heavy losses in energy, then this process can enable a single-junction solar cell to surpass the Shockley-Queisser limit. While singlet fission processes are commonly observed in several materials, harvesting the resulting triplets is difficult and has been demonstrated with only a few transport materials. Here, transient absorption spectroscopy is used to investigate singlet fission and carrier transfer processes at the AgBiS₂ /pentacene (AgBiS₂ /Pc) heterojunction. The successful transfer of triplets from pentacene to AgBiS₂ and the transfer of holes from AgBiS₂ to pentacene is observed. Further singlet fission in pentacene by modifying the crystallinity of the pentacene layer and have fabricated the first singlet fission AgBiS₂ /Pc solar cell is enhanced. Singlet fission devices exhibit higher external quantum efficiency compared with the control devices, and thus demonstrating the significant contribution of charges from the singlet fission process.

Photoelectrochemical immunoassay of squamous cell carcinoma antigen based on CuO/nitrogen-doped porous carbon-ZnO biolabeling and a type-II In2O3/AgBiS2 heterojunction

AgBiS₂ was hydrothermally synthesized, In₂O₃ was synthesized by hydrothermal method and calcination, and the type-II In₂O₃/AgBiS₂ heterojunction material of an optimized composition ratio was cast-coated on a fluorine-doped tin oxide (FTO) slice to fabricate an In₂O₃/AgBiS₂/FTO photoanode. The signal-attenuated photoelectrochemistry sandwich immunoassay of squamous cell carcinoma antigen (SCCA) was realized on this photoanode, on the basis of a bovine serum albumin/secondary antibody/CuO nanoparticles/nitrogen-doped porous carbon-ZnO bionanocomposite that can competitively absorb light and deplete the electron donor ascorbic acid as well as show the steric hindrance and p-n quenching effects. Under the optimized conditions (e.g., at a bias of 0 V vs. SCE), the photocurrent was linear with the common logarithm of SCCA concentration from 2.00 pg mL^-1 to 50.0 ng mL^-1, with a limit of detection (LOD) of 0.62 pg mL^-1 (S/N = 3). The immunoassay of SCCA in human serum samples gave satisfactory recovery (92.0~103%) and relative standard deviation (5.1~7.8%) results.

Optoelectronic Modulation of Silver Antimony Sulfide Thin Films for Photodetection

Silver antimony sulfide, as a ternary chalcogenide, has attracted great attention in the field of optoelectronics in recent years. In particular, it has appealing properties, such as excellent stability, solution processability, and versatile composition tunability. Benefiting from the recent development of processing techniques, AgSbS₂ has emerged as a promising candidate for next-generation, thin-film photovoltaics. On the contrary, AgSbS₂-based photodetectors have been barely reported. In this work, we systematically investigated the composition engineering of silver antimony sulfide compounds with a precursor route. Their optoelectronic properties were fully characterized, and the composition was optimized for photodetection. High-performance phototransistors were first reported based on field-effect thin film transistors with interfacial modification. The obtained AgSbS₂ phototransistors exhibited relatively high photosensitivity, low dark current and noise, superior device stability, and excellent detectivity covering the whole range from ultraviolet to near-infrared, highlighting the great potential for next-generation photodetection.

Atomic periodic engineering enabled ultrathin high-efficiency AgBiS2 solar cells

The periodic engineering of AgS6 and BiS6 octahedrons is demonstrated. The modulated AgBiS2 achieves a spectroscopic limited maximum efficiency as high as 29.7% with an ultrathin thickness of 100 nm.