Scalable Indium Phosphide Thin-Film Nanophotonics Platform for Photovoltaic and Photoelectrochemical Devices

Design and Optimization of a Self-Protected Thin Film c-Si Solar Cell against Reverse Bias

Current mismatch due to solar cell failure or partial shading of solar panels may cause a reverse biasing of solar cells inside a photovoltaic (PV) module. The reverse-biased cells consume power instead of generating it, resulting in hot spots. To protect the solar cell against the reverse current, we introduce a novel design of a self-protected thin-film crystalline silicon (c-Si) solar cell using TCAD simulation. The proposed device achieves two distinct functions where it acts as a regular solar cell at forward bias while it performs as a backward diode upon reverse biasing. The ON-state voltage (V_ON) of the backward equivalent diode is found to be 0.062 V, which is lower than the value for the Schottky diode usually used as a protective element in a string of solar cells. Furthermore, enhancement techniques to improve the electrical and optical characteristics of the self-protected device are investigated. The proposed solar cell is enhanced by optimizing different design parameters, such as the doping concentration and the layers' thicknesses. The enhanced cell structure shows an improvement in the short-circuit current density (J_SC) and the open-circuit voltage (V_OC), and thus an increased power conversion efficiency (PCE) while the V_ON is increased due to an increase of the J_SC. Moreover, the simulation results depict that, by the introduction of an antireflection coating (ARC) layer, the external quantum efficiency (EQE) is enhanced and the PCE is boosted to 22.43%. Although the inclusion of ARC results in increasing V_ON, it is still lower than the value of V_ON for the Schottky diode encountered in current protection technology.

Ordered nanostructures arrays fabricated by anodic aluminum oxide (AAO) template-directed methods for energy conversion

Clean and efficient energy conversion systems can overcome the depletion of the fossil fuel and meet the increasing demand of the energy. Ordered nanostructures arrays convert energy more efficiently than their disordered counterparts, by virtue of their structural merits. Among various fabrication methods of these ordered nanostructures arrays, anodic aluminum oxide (AAO) template-directed fabrication have drawn increasing attention due to its low cost, high throughput, flexibility and high structural controllability. This article reviews the application of ordered nanostructures arrays fabricated by AAO template-directed methods in mechanical energy, solar energy, electrical energy and chemical energy conversions in four sections. In each section, the corresponding advantages of these ordered nanostructures arrays in the energy conversion system are analysed, and the limitation of the to-date research is evaluated. Finally, the future directions of the ordered nanostructures arrays fabricated by AAO template-directed methods (the promising method to explore new growth mechanisms of AAO, green fabrication based on reusable AAO templates, new potential energy conversion application) are discussed.

A Novel Nanocone Cluster Microstructure with Anti-reflection and Superhydrophobic Properties for Photovoltaic Devices

As three-dimensional (3D) nanostructures can significantly improve the absorption capacity of photons, it is widely used in various photovoltaic devices. However, the high-cost and complex preparation process of traditional 3D nanostructures restricted its development greatly. In this paper, a new type of nanocone cluster microstructure was prepared on polydimethylsiloxane (PDMS) substrate by using a simple template process. This novel nanocone cluster microstructure can significantly improve the light transmittance and reduce the light reflection, showing superior anti-reflection property. In the whole range of visible band, the nanocone cluster microstructure effectively reduces the reflectivity of the light, so that it remains below 3.5%. In addition, this kind of cluster microstructure showed excellent superhydrophobic property and self-cleaning ability with the contact angle of 151°.

Antireflective Paraboloidal Microlens Film for Boosting Power Conversion Efficiency of Solar Cells

Microlens arrays can improve light transmittance in optical devices or enhance the photoelectrical conversion efficiency of photovoltaic devices. Their surface morphology (aspect ratio and packed density) is vital to photon management in solar cells. Here, we report a 100% packed density paraboloidal microlens array (PMLA), with a large aspect ratio, fabricated by direct-write UV laser photolithography coupled with soft imprint lithography. Optical characterization shows that the PMLA structure can remarkably decrease the front-side reflectance of solar cell device. The measured electrical parameters of the solar cell device clearly and consistently demonstrate that the PMLA film can considerably improve the photoelectrical conversion efficiency. In addition, the PMLA film has superhydrophobic properties, verified by measurement of a large water contact angle, and can enhance the self-cleaning capability of solar cell devices.

Confined Liquid-Phase Growth of Crystalline Compound Semiconductors on Any Substrate

The growth of crystalline compound semiconductors on amorphous and non-epitaxial substrates is a fundamental challenge for state-of-the-art thin-film epitaxial growth techniques. Direct growth of materials on technologically relevant amorphous surfaces, such as nitrides or oxides results in nanocrystalline thin films or nanowire-type structures, preventing growth and integration of high-performance devices and circuits on these surfaces. Here, we show crystalline compound semiconductors grown directly on technologically relevant amorphous and non-epitaxial substrates in geometries compatible with standard microfabrication technology. Furthermore, by removing the traditional epitaxial constraint, we demonstrate an atomically sharp lateral heterojunction between indium phosphide and tin phosphide, two materials with vastly different crystal structures, a structure that cannot be grown with standard vapor-phase growth approaches. Critically, this approach enables the growth and manufacturing of crystalline materials without requiring a nearly lattice-matched substrate, potentially impacting a wide range of fields, including electronics, photonics, and energy devices.

Mimicking Biological Synaptic Functionality with an Indium Phosphide Synaptic Device on Silicon for Scalable Neuromorphic Computing

Neuromorphic or "brain-like" computation is a leading candidate for efficient, fault-tolerant processing of large-scale data as well as real-time sensing and transduction of complex multivariate systems and networks such as self-driving vehicles or Internet of Things applications. In biology, the synapse serves as an active memory unit in the neural system and is the component responsible for learning and memory. Electronically emulating this element via a compact, scalable technology which can be integrated in a three-dimensional (3-D) architecture is critical for future implementations of neuromorphic processors. However, present day 3-D transistor implementations of synapses are typically based on low-mobility semiconductor channels or technologies that are not scalable. Here, we demonstrate a crystalline indium phosphide (InP)-based artificial synapse for spiking neural networks that exhibits elasticity, short-term plasticity, long-term plasticity, metaplasticity, and spike timing-dependent plasticity, emulating the critical behaviors exhibited by biological synapses. Critically, we show that this crystalline InP device can be directly integrated via back-end processing on a Si wafer using a SiO₂ buffer without the need for a crystalline seed, enabling neuromorphic devices that can be implemented in a scalable and 3-D architecture. Specifically, the device is a crystalline InP channel field-effect transistor that interacts with neuron spikes by modification of the population of filled traps in the MOS structure itself. Unlike other transistor-based implementations, we show that it is possible to mimic these biological functions without the use of external factors (e.g., surface adsorption of gas molecules) and without the need for the high electric fields necessary for traditional flash-based implementations. Finally, when exposed to neuronal spikes with a waveform similar to that observed in the brain, these devices exhibit the ability to learn without the need for any external potentiating/depressing circuits, mimicking the biological process of Hebbian learning.

Plasma-Assisted Large-Scale Nanoassembly of Metal-Insulator Bioplasmonic Mushrooms

Large-scale plasmonic substrates consisting of metal-insulator nanostructures coated with a biorecognition layer can be exploited for enhanced label-free sensing by utilizing the principle of localized surface plasmon resonance (LSPR). Most often, the uniformity and thickness of the biorecognition layer determine the sensitivity of plasmonic resonances as the inherent LSPR sensitivity of nanomaterials is limited to 10-20 nm from the surface. However, because of time-consuming nanofabrication processes, there is limited work on both the development of large-scale plasmonic materials and the subsequent surface functionalizing with biorecognition layers. In this work, by exploiting properties of reactive ions in an SF₆ plasma environment, we are able to develop a nanoplasmonic substrate containing ∼10⁶/cm² mushroom-like structures on a large-sized silicon dioxide substrate (i.e., 2.5 cm by 7.5 cm). We further investigate the underlying mechanism of the nanoassembly of gold on glass inside the plasma environment, which can be expanded to a variety of metal-insulator systems. By incorporating a novel microcontact printing technique, we deposit a highly uniform biorecognition layer of proteins on the nanoplasmonic substrate. The bioplasmonic assays performed on these substrates achieve a limit of detection of 10^-17 g/mL (∼66 zM) for biomolecules such as antibodies (∼150 kDa). Our simple nanofabrication procedure opens new opportunities in fabricating versatile bioplasmonic materials for a wide range of biomedical and sensing applications.