Hybrid black silicon solar cells textured with the interplay of copper-induced galvanic displacement

Effect of Cuprous Oxide Nanocubes and Antimony Nanorods on the Performance of Silicon Nanowire-Based Quasi-Solid-State Solar Cell

Antimony nanorods (SbNRs) anchored to vertically aligned SiNWs serve as cosensitizers and enhance the light absorption of NWs, and their favorably positioned valence band (VB) coupled with their p-type semiconducting nature allows fast hole extraction from SiNWs. Photocorrosion of SiNWs is effectively prevented by a monolayer of N-[3-(trimethoxysilyl)propyl]aniline (TMSPA). Upon assembling a quasi-solid-state solar cell with a SbNRs@TMSPA@SiNW photoanode, a triiodide-iodide (I₃ ^-/I^-) redox couple-based gel encompassing dispersed p-type cuprous oxide nanocubes (Cu₂O NCs) as the hole transport material. and an electrocatalytic NiO as the counter electrode, a power conversion efficiency (PCE) of 4.7% (under 1 sun) is achieved, which is greater by 177% relative to an analogous cell devoid of the Cu₂O NCs and SbNRs. SbNRs at the photoanode maximize charge separation and suppress electron-hole and electron-I₃ ^- recombination at the photoanode/electrolyte interface, thereby improving the overall current collection efficiency. Concurrently, the Cu₂O NCs facilitate hole scavenging from SbNRs or SiNWs and relay them rapidly to the I^- ions in the electrolyte. Optically transparent and mesoporous NiO with a VB conducive to accepting electrons from FTO permits abundant interaction with I₃ ^- ions. The high PCE is a cumulative outcome of the synergistic attributes of SbNRs, Cu₂O NCs, and NiO. The SbNRs@TMSPA@SiNWs/Cu₂O-gel/NiO solar cell also exhibits a noteworthy operational stability, for it endures 500 h of continuous 1 sun illumination accompanied by an ∼24.4% drop in its PCE. The solar cell architecture in view of the judiciously chosen components with favorable energy level offsets, semiconducting/photoactive properties, and remarkable stability opens up pathways to adapt these materials to other solar cells as well.

Light Trapping of Inclined Si Nanowires for Efficient Inorganic/Organic Hybrid Solar Cells

Light/matter interaction of low-dimensional silicon (Si) strongly correlated with its geometrical features, which resulted in being highly critical for the practical development of Si-based photovoltaic applications. Yet, orientation modulation together with apt control over the size and spacing of aligned Si nanowire (SiNW) arrays remained rather challenging. Here, we demonstrated that the transition of formed SiNWs with controlled diameters and spacing from the crystallographically preferred <100> to <110> orientation was realized through the facile adjustment of etchant compositions. The underlying mechanism was found to correlate with the competing reactions between the formation and removal of oxide at Ag/Si interfaces that could be readily tailored through the concentration ratio of HF to H2O2. By employing inclined SiNWs for the construction of hybrid solar cells, the improved cell performances compared with conventional vertical-SiNW-based hybrid cells were demonstrated, showing the conversion efficiency of 12.23%, approximately 1.12 times higher than that of vertical-SiNW-based hybrid solar cells. These were numerically and experimentally interpreted by the involvement of excellent light-trapping effects covering the wide-angle light illuminations of inclined SiNWs, which paved the potential design for next-generation optoelectronic devices.

Mesopore Formation and Silicon Surface Nanostructuration by Metal-Assisted Chemical Etching With Silver Nanoparticles

This article presents a study on Metal-Assisted Chemical Etching (MACE) of silicon in HF-H₂O₂ using silver nanoparticles as catalysts. Our aim is a better understanding of the process to elaborate new 3D submicrometric surface structures useful for light management. We investigated MACE over the whole range of silicon doping, i.e., p⁺⁺, p⁺, p, p^-, n, n⁺, and n⁺⁺. We discovered that, instead of the well-defined and straight mesopores obtained in p and n-type silicon, in p⁺⁺ and n⁺⁺ silicon MACE leads to the formation of cone-shaped macropores filled with porous silicon. We account for the transition between these two pore-formation regimes (straight and cone-shaped pores) by modeling (at equilibrium and under polarization) the Ag/Si/electrolyte (HF) system. The model simulates the system as two nanodiodes in series. We show that delocalized MACE is explained by a large tunnel current contribution for the p-Si/Ag and n-Si/HF diodes under reverse polarization, which increases with the doping level and when the size of the nanocontacts (Ag, HF) decreases. By analogy with the results obtained on heavily doped silicon, we finally present a method to form size-controlled cone-shaped macropores in p silicon with silver nanoparticles. This shape, instead of the usual straight mesopores, is obtained by applying an external anodic polarization during MACE. Two methods are shown to be effective for the control of the macropore cone angle: one by adjusting the potential applied during MACE, the other by changing the H₂O₂ concentration. Under appropriate etching conditions, the obtained macropores exhibit optical properties (reflectivity ~3 %) similar to that of black silicon.

Fabrication of an Efficient Planar Organic-Silicon Hybrid Solar Cell with a 150 nm Thick Film of PEDOT: PSS

Organic–inorganic hybrid solar cells composed of p-type conducting polymer poly (3,4-ethylene-dioxythiophene): polystyrenesulfonate (PEDOT: PSS) and n-type silicon (Si) have gained considerable interest in recent years. From this viewpoint, we present an efficient hybrid solar cell based on PEDOT: PSS and the planar Si substrate (1 0 0) with the simplest and cost-effective experimental procedures. We study and optimize the thickness of the PEDOT: PSS film to improve the overall performance of the device. We also study the effect of ethylene glycol (EG) by employing a different wt % as a solvent in the PEDOT: PSS to improve the device’s performance. Silver (Ag) was deposited by electron beam evaporation as the front and rear contacts for the solar cell device. The whole fabrication process was completed in less than three hours. A power conversion efficiency (PCE) of 5.1%, an open circuit voltage (Voc) of 598 mV, and a fill factor (FF) of 58% were achieved.

Self-formed silver nanoparticles on freestanding silicon nanowire arrays featuring SERS performances

Herein, the universal luminescence characteristics of porous Si nanowire arrays were exploited using a wide range of doping types and concentrations; we found that the dual-band photoluminescence intensities were correlated with the formation rates of Si nanowires with porous features; however, these intensities exhibited no evident dependence on the doping conditions. Furthermore, we demonstrated a facile and reliable transfer method implementing the freestanding Si nanowire arrays while maintaining the robust photoluminescence behaviors under bending conditions. The fabrication protocol, involving lateral etching locally at the nanowire ends, enabled the controlled formation of uniform and large-area transferred nanowires with vertical regularity. Without the additional deposition of Ag nanoparticles, these transferred Si nanowire films inherently possessed SERS sensing capability with a relative enhancement factor over 1.8 times that of the Si nanowires with electroless-deposited Ag nanoparticles, which could practically emerge as a functional design for the integration of practical biochip devices.

ZnO/Cu2O/Si Nanowire Arrays as Ternary Heterostructure-Based Photocatalysts with Enhanced Photodegradation Performances

Ternary ZnO/Cu2O/Si nanowire arrays with vertical regularity were prepared with all-solution processed method at low temperature. In addition to the detailed characterizations of morphologies and crystallographic patterns, the analyses of photoluminescence and photocurrents revealed the sound carrier separation owing from the established step-like band structures. By modeling the photodegradation process of the prepared heterostructures through kinetic investigations and scavenger examinations, the photocatalytic removal of MB dyes was found to follow the second-order kinetic model with reaction constant more than 15.3 times higher than bare Si nanowires and achieved 5.7 times and 3.4 times than ZnO/Si and Cu2O/Si binary heterostructures, respectively. Moreover, the highly stable photoactivity of ZnO/Cu2O/Si photocatalysts was evidenced from the repeated photodegradation tests, which demonstrated the robust photocatalytic efficiency after cycling uses. The facile synthesis along with in-depth mechanism study of such ternary heterostructures could be potential for practical treatment for organic pollutants. KEYWORDS: HeterostructurePhotocatalystSilicon nanowire arraysKinetic study.

Tailoring the robust superhydrophobic silicon textures with stable photodetection properties

Surface hydrophobicity of silicon with sound durability under mechanical abrasion is highly desirable for practical needs. However, the reported micro-pyramid/nanowires structures suffer from the saturation characteristics of contact angle at around 132 degree, which impede the promotions toward reaching the state of superhydrophobicity. The present study focuses on the realization of two-scale silicon hierarchical structures prepared with the facile, rapid and large-area capable chemical etching methods without the need of lithographic patterning. The designed structures, with the well combination of microscale inverted pyramids and nanowire arrays, dramatically lead to the increased wetting angle of 157.2 degree and contact-angle hysteresis of 9.4 degree. In addition, the robustness test reveals that these hierarchical textures possess the narrow contact-angle change of 4 degree responding to the varied pH values, and maintain a narrow deviation of 2 degree in wetting angle after experiencing the abrasion test. Moreover, the highly stable photodetection characteristics of such two-scale structures were identified, showing the reliable photocurrents with less than 3% of deviation under wide range of environmental humidity. By adopting a simple chemical treatment, the wetting control is demonstrated for reliable transition of superhydrophobicity and superhydrophilicity.

Silicon Nanocanyon: One-Step Bottom-Up Fabrication of Black Silicon via in-Lasing Hydrophobic Self-Clustering of Silicon Nanocrystals for Sustainable Optoelectronics

We report a novel one-step bottom-up fabrication method for multiscale-structured black Si, which is characterized by randomly distributed microscale Si layers covered with sub-100 nm protrusions with submicron boundary grooves. The unique multiscale structure, suggested as a "nanocanyon," effectively minimizes light reflection over a broad spectrum by diversifying the scattering routes from the nanotextured surface to the wide distributed boundary micronanoscale grooves. This structure was achieved by hydrophobic clustering and local aggregation of instantaneously melted Si nanocrystals on a glass substrate under laser irradiation. This method can replace the complicated conventional silicon processes, such as patterning for selective Si formation, texturing for improved absorption, and doping for modifying the electrical properties, because the proposed method obviates the need for photolithography, chemical etching, vacuum processes, and expensive wafers. Finally, black Si photosensor arrays were successfully demonstrated by a low-cost solution process and a laser growth sintering technique for microchannel fabrication. The results show the great potential of the proposed fabrication method for low-cost and sustainable production of highly sensitive optoelectronics and as an alternative to conventional wafer-based photosensor manufacturing techniques.

Efficient Photocatalysts Made by Uniform Decoration of Cu2O Nanoparticles on Si Nanowire Arrays with Low Visible Reflectivity

Highly uniformed decorations of Cu₂O nanoparticles on the sidewalls of silicon nanowires (SiNWs) with high aspect ratio were prepared through a two-step electroless deposition at room temperature. Morphology evolutions and photocatalytic performance of SiNWs decorated with aggregated and dispersed Cu₂O nanoparticles were unveiled, and the correlated photodegradation kinetics was identified. In comparison with the conventional direct loadings where the aggregated Cu₂O/SiNW structures were created, the uniform incorporation of Cu₂O with SiNWs exhibited more than three and nine times of improved photodegradation efficiency than the aggregated-Cu₂O/SiNWs and sole SiNWs, respectively.

Anti-Reflectance Optimization of Secondary Nanostructured Black Silicon Grown on Micro-Structured Arrays

Owing to its extremely low light absorption, black silicon has been widely investigated and reported in recent years, and simultaneously applied to various disciplines. Black silicon is, in general, fabricated on flat surfaces based on the silicon substrate. However, with three normal fabrication methods-plasma dry etching, metal-assisted wet etching, and femtosecond laser pulse etching-black silicon cannot perform easily due to its lowest absorption and thus some studies remained in the laboratory stage. This paper puts forward a novel secondary nanostructured black silicon, which uses the dry-wet hybrid fabrication method to achieve secondary nanostructures. In consideration of the influence of the structure's size, this paper fabricated different sizes of secondary nanostructured black silicon and compared their absorptions with each other. A total of 0.5% reflectance and 98% absorption efficiency of the pit sample were achieved with a diameter of 117.1 μm and a depth of 72.6 μm. In addition, the variation tendency of the absorption efficiency is not solely monotone increasing or monotone decreasing, but firstly increasing and then decreasing. By using a statistical image processing method, nanostructures with diameters between 20 and 30 nm are the majority and nanostructures with a diameter between 10 and 40 nm account for 81% of the diameters.

Solution-processed ZnO/Si based heterostructures with enhanced photocatalytic performance

Well-incorporated ZnO/SiNW arrays with reliable photocatalytic activity were prepared by an all-solution processed method.