Satria Zulkarnaen Bisri

Epitaxially connected quantum dot superlattices (Epi-QDSLs) represent a promising platform for high-performance, next-generation photodetectors. Their enhanced electron transport mobility, together with the preservation of quantum confinement, enables efficient charge extraction with high quantum efficiency. This results in high responsivity, detectivity, and faster response time. The ligand-free nature of PbS quantum dots (QDs) in Epi-QDSLs introduces a critical challenge of poor environmental stability, as the conventional surface passivation strategies of ligand exchange are incompatible with ligand-free QDs in the Epi-QDSL system. Here, we examine the air stability of the Epi-QDSL photodetector and investigate the effects of introducing a P(VDF-TrFE) passivation layer on the material properties, device performance, and air stability of Epi-QDSL. The dipole polarization of the dielectric nature of the block copolymer induces an electrostatic n-type doping effect, as confirmed by the field-effect transistor measurement. This doping effect increases electron mobility and facilitates more efficient charge extraction, thereby significantly improving device performance. The hydrophobic nature of P(VDF-TrFE) effectively prevents the progressive infiltration of oxygen and moisture into the PbS QDs, thereby preventing the irreversible degradation suffered by the ligand-free QDs in the Epi-QDSL system.

Charge-carrier transport in semiconductor colloidal quantum dot (CQD) solids has been the subject of extensive debate and investigation for more than a decade. Understanding the underlying transport mechanisms in CQD assemblies is critical for unlocking their full potential in optoelectronic applications. To date, a widely accepted view holds that carrier transport in conventional ligand-capped glassy CQD solids is a non-adiabatic hopping process, supported by both experimental observations and theoretical models. In contrast, recent advances have enabled the self-assembly of CQDs into long-range-ordered superlattices with epitaxial connections between neighboring QDs. These superlattices are expected by many to exhibit band-like transport, potentially overcoming the limitations of hopping conduction in disordered systems. However, definitive experimental evidence and a comprehensive theoretical framework for charge transport in such highly ordered structures remain lacking. While the formation mechanisms of these superlattices have been widely explored, this Perspective aims to provide insight into the current understanding of charge-carrier transport in epitaxially connected CQD superlattices.

Colloidal semiconductor quantum dots (QDs) are among the promising materials for optoelectronic device applications, including photodetectors. Their size‐tunable bandgap enables wide‐range wavelength photodetection from the visible to the mid‐infrared regime. Most recently, the realization of epitaxially‐connected quantum dot superlattices (QDSLs) addresses one of the critical challenges associated with assemblies of QDs and their electronic transport. These epitaxially‐connected QDSLs demonstrated the possibility of delocalized charge transport, which could improve the electrical transport performance of QD‐based devices. On the other hand, delocalized charge carriers might affect the quantum confinement effect, potentially reducing the merits of QDs for optoelectronic device performance. Here, we demonstrate high‐performance photodetectors based on a monolayer of quasi‐2D epitaxially connected PbS QDSLs, exhibiting higher responsivity and detectivity than those of conventional short‐ligand‐capped QD assemblies. The remarkable photodetection enhancement can be indicated from several aspects: (i) the light intensity‐dependent characteristics reveal evidence of a low trap density within the epitaxially‐connected superlattice, (ii) the time‐resolved measurements show a faster response time and a two‐step charge carrier dynamic, (iii) the wavelength‐dependent analysis further suggests the occurrence of multiple exciton generation under high‐energy photon excitation. These findings establish the epitaxially‐connected QDSL as an optoelectronic metamaterial, an up‐and‐coming candidate for next‐generation, high‐performance photodetectors.

Precise synthesis control and structural determination of AgBiS ₂ NC formation allow the demonstration of high-performance photodetector devices.

The growing need for high-performance computing continues to drive improvement in circuit and device technologies, particularly with respect to speed and power efficiency. Device scaling remains the most effective strategy for meeting circuit performance requirements while reducing power consumption. Thanks to their solution processability, colloidal semiconductor quantum dots (QDs) are highly suitable for device miniaturisation as quantum information science platforms. Quantum mechanical effects must be carefully considered when designing nanometre-scale electronic devices (i.e., transistors) that incorporate a single QD. Here, we demonstrate a resonant tunnelling transistor (RTT) based on a single lead sulfide (PbS) QD anchored by a bidentate ligand molecule attached to heteroepitaxial spherical Au/Pt nanogap electrodes. Five negative differential resistances (NDRs) were observed at both positive and negative drain voltages in output characteristics, which could be attributed to the formation of a double-barrier “quantum well” structure with the strong Fermi level pinning of the discrete energy level of the QD to one electrode. Furthermore, these NDRs could be tuned by applying a gate electric field, which will become one of the keys for enabling quantum and neuromorphic electronics. This demonstration of single PbS-QD-based RTTs paves the way for sub-10 nm solution-processable quantum electronic devices.

Colloidal quantum dots (CQDs) show unique properties that distinguish them from their bulk form, the so-called quantum confinement effects. This feature manifests in tunable size-dependent band gaps and discrete energy levels, resulting in distinct optical and electronic properties. The investigation direction of colloidal quantum dots (CQDs) materials has started switching from high-performing materials based on Pb and Cd, which raise concerns regarding their toxicity, to more environmentally friendly compounds, such as AgBiS₂. After the first breakthrough in solar cell application in 2016, the development of AgBiS₂ QDs has been relatively slow, and many of the fundamental physical and chemical properties of this material are still unknown. Investigating the growth of AgBiS₂ QDs is essential to understanding the fundamental properties that can improve this material’s performance. This review comprehensively summarizes the synthesis strategies, ligand choice, and solar cell fabrication of AgBiS₂ QDs. The development of PbS QDs is also highlighted as the foundation for improving the quality and performance of AgBiS₂ QD. Furthermore, we prospectively discuss the future direction of AgBiS₂ QD and its use for solar cell applications.