Doped heavy metal-free III – V semiconductor nanocrystal quantum dots are of great interest both from the fundamental aspects of doping in highly confined structures, and from the applicative side of utilizing such building blocks in the fabrication of p-n homojunction devices. InAs nanocrystals, that are of particular relevance for short wave IR detection and emission applications, manifest heavy n-type character poising a challenge for their transition to p-type behavior. We present p-type doping of InAs nanocrystals with Zn – enabling control over the charge carrier type in InAs QDs field effect transistors. The post-synthesis doping reaction mechanism is studied for Zn precursors with varying reactivity. Successful p-type doping was achieved by the more reactive precursor, diethylzinc. Substitutional doping by Zn²⁺ replacing In³⁺ is established by X-ray absorption spectroscopy analysis. Furthermore, enhanced near IR photoluminescence is observed due to surface passivation by Zn as indicated from elemental mapping utilizing high resolution electron microscopy corroborated by X-ray photoelectron spectroscopy study. The demonstrated ability to control the carrier type, along with the improved emission characteristics, paves the way towards fabrication of optoelectronic devices active in the short wave IR region utilizing heavy-metal free nanocrystal building blocks.

This article is protected by copyright. All rights reserved

Organic-based solar cells have developed for the last three decades. Moving forward generally requires the assistance of useful models that are adapted to currently used materials and device architectures. The least understood part of the charge generation is the first step of the exciton dissociation, and new or refined models are being suggested. However, many of today's questions have been asked before, going back almost an entire century. We have gone to the 1930s and attempted to critically review significant contributions on equal footing. We find that Onsager's and Frenkel's models have a similar foundation but were developed to suit very different materials (ions in solutions vs electrons in semiconductors). The contribution by Braun or the Onsager–Braun model can be considered wrong, yet it was instrumental for the field's development. The community practically ignores one of the most promising models (Arkhipov–Baranovskii). Hot exciton dissociation has many faces due to “hot” being a relative term and/or the heat being stored in different ways (electronic, vibronic, etc.). Entropy considerations are instrumental in simplifying the picture, yet they add no physics compared to the full-3D models. We hope that by emphasizing the physical picture of the various models and the underlying assumptions, one could use them as a stepping stone to the next generation models.

The mixed ionic–electronic nature of lead halide perovskites makes their performance in solar cells complex in nature. Ion migration is often associated with negative impacts─such as hysteresis or device degradation─leading to significant efforts to suppress ionic movement in perovskite solar cells. In this work, we demonstrate that ion trapping at the perovskite/electron transport layer interface induces band bending, thus increasing the built-in potential and open-circuit voltage of the device. Quantum chemical calculations reveal that iodine interstitials are stabilized at that interface, effectively trapping them at a remarkably high density of ∼1021 cm–3 which causes the band bending. Despite the presence of this high density of ionic defects, the electronic structure calculations show no sub-band-gap states (electronic traps) are formed due to a pronounced perovskite lattice reorganization. Our work demonstrates that ionic traps can have a positive impact on device performance of perovskite solar cells.

Schottky diodes based on inexpensive materials that can be processed using simple manufacturing methods are of particular importance for the next generation of flexible electronics. Although a number of high-frequency n-type diodes and rectifiers have been demonstrated, the progress with p-type diodes is lagging behind, mainly due to the intrinsically low conductivities of existing p-type semiconducting materials that are compatible with low-temperature, flexible, substrate-friendly processes. Herein, we report on CuSCN Schottky diodes, where the semiconductor is processed from solution, featuring coplanar Al–Au nanogap electrodes (<15 nm), patterned via adhesion lithography. The abundant CuSCN material is doped with the molecular p-type dopant fluorofullerene C₆₀F₄₈ to improve the diode’s operating characteristics. Rectifier circuits fabricated with the doped CuSCN/C₆₀F₄₈ diodes exhibit a 30-fold increase in the cutoff frequency as compared to pristine CuSCN diodes (from 140 kHz to 4 MHz), while they are able to deliver output voltages of >100 mV for a V_IN = ±5 V at the commercially relevant frequency of 13.56 MHz. The enhanced diode and circuit performance is attributed to the improved charge transport across CuSCN induced by C₆₀F₄₈. The ensuing diode technology can be used in flexible complementary circuits targeting low-energy-budget applications for the emerging internet of things device ecosystem.

Metal oxide-based electronics is advancing rapidly where the reduced dimensions require transistor structures different to conventional CPUs. The double injection function transistor (DIFT) is a type of a source-controlled transistor. As doping is a facile method in the semiconductor industry, we suggest that the DIFT can be realized through a doping pattern under the source electrode. We show that double doping functions similarly to the double work function DIFT, recently demonstrated. We use device simulations to analyze the operation principle of the DIFT structure and provide design guidelines. We find that the structural separation of the injection and depletion functions allows adapting the transistor structure to fabrication process limitations. A 200 nm channel length InGaZnO based device can be designed to exhibit proper saturation at sub-1 V drain bias.

The low carrier mobility of organic semiconductors and the high parasitic resistance and capacitance often encountered in conventional organic Schottky diodes, hinder their deployment in emerging radio frequency (RF) electronics. Here we overcome these limitations by combining self-aligned asymmetric nanogap electrodes (∼25 nm) produced by adhesion-lithography, with a high mobility organic semiconductor and demonstrate RF Schottky diodes able to operate in the 5G frequency spectrum. We used C₁₆IDT-BT, as the high hole mobility polymer, and studied the impact of p-doping on the diode performance. Pristine C₁₆IDT-BT-based diodes exhibit maximum intrinsic and extrinsic cutoff frequencies (f_C) of >100 and 6 GHz, respectively. This extraordinary performance is attributed primarily to the planar nature of the nanogap channel and the diode's small junction capacitance (< 2 pF). Doping of C₁₆IDT-BT with the molecular p-dopant C₆₀F₄₈, improves the diode's performance further by reducing the series resistance resulting to intrinsic and extrinsic f_C of >100 and ∼14 GHz respectively, while the DC output voltage of a RF rectifier circuit increases by a tenfold. Our work highlights the importance of the planar nanogap architecture and paves the way for the use of organic Schottky diodes in large-area radio frequency electronics of the future.

Tremendous progress in employing metal halide perovskites (MHPs) in a variety of applications, especially in photovoltaics, has been made in the past decade. To unlock the full potential of MHP materials in optoelectronic devices, an improved understanding of the electronic energy level alignment at perovskite-based interfaces is required. This particularly pertains to such interfaces under device operation conditions, e.g. under illumination with visible light such as in a solar cell. Herein, it is revealed that the energy level alignment at the buried interface between a double cation lead halide perovskite film and charge-selective organic transport layers changes upon white light illumination. This is found from photoemission experiments performed with the samples in dark and under illumination, and the interfacial energy level shift is reversible. The underlying mechanism is attributed to the accumulation of one charge carrier type within the perovskite film at the interface under illumination, as a result of the charge-selective nature of the organic layer. The fact that the interfacial energy level alignment at MHP-based junctions under illumination can differ from that in dark is to be taken into account to fully rationalize device characteristics.

Revisiting the intensity-dependent quantum efficiency (IDQE) technique in the context of non-fullerene acceptors, we find that at forward-bias conditions, the response exhibits what seems to be anomalous behavior that is not consistent with light excitation induced trap filling. Analysis based on the Shockley–Read–Hall model leads to the conclusion that the contacts cause the traps to be completely full in the dark. The role of the light excitation is to half-empty the traps, and thus, the “anomalous” behavior is created. By fitting the IDQE at several bias levels, we find that the trapping is consistent with multiphonon capture by a state close to the middle of the gap. As trap-assisted recombination is a significant loss mechanism, it is essential to fully monitor it for indoor applications as well as to cross the single junction 20% power conversion efficiency limit.

We propose and demonstrate self-aligned Double Injection Function Thin Film Transistor (DIF-TFT) architecture that mitigates short channel effects in 200 nm channel on non-scaled insulator (100 nm SiO₂). In this conceptual design, a combination of ohmic-like injection contact and a high injection-barrier metal allows maintaining the high ON currents while suppressing drain-induced barrier lowering (DIBL) effects. Using an industrial 2-D device simulator (Sentaurus), we propose two methods to realize the DIF concept. We use one of them to demonstrate, experimentally, a DIF-TFT based on solution-processed indium gallium zinc oxide (IGZO). Using molybdenum as the ohmic contact and platinum as the high injection barrier, we compare three transistors’ source-contacts: ohmic, Schottky, and DIF. The fabricated DIF-TFT exhibits saturation at sub 1 V drain bias with only about a factor of 2 loss in ON current compared to the ohmic contact.

The polycrystalline nature of perovskite thin films suggests that the nonradiative recombination losses may be grain size dependent. We use measured grain size distributions of methylammonium lead triiodide layers to describe the macroscopic solar cell as composed of multiple single grain size cells operating in parallel. Using a model, we show that the grain size distribution results in spatial dispersion of the local open-circuit voltage (0.9–1.15 V), fill factor (50–82%), and power conversion efficiency (7.5–19%). When the device is held at open-circuit voltage, there is significant current exchange between large and small grains. Smaller grains are a “parasitic shunt” for the larger grains.