Sudong Wu

Ideal rear contact formed via employing a conjugated polymer for Si/PEDOT:PSS hybrid solar cells

Recently, Si/organic polymer hybrid solar cells have been widely studied as the candidate for low-cost photovoltaics due to the simple low-temperature fabrication process. However, the rear electrode typically formed by directly depositing Al on the n-type Si is a Schottky contact, severely impacting the electron collecting efficiency. Here, an alcohol soluble polymer, poly[(9,9-bis(3′-(N,N-diethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN), is firstly introduced to the Al/n-Si interface to improve the contact property, resulting in a remarkable reduced work function of the Al electrode and thus a good ohmic contact. An excellent photovoltaic efficiency of 13.35% is achieved in a planar device with a PFN layer. The facilitated electron collection efficiency associated with the ohmic contact not only improves the fill factor, but also enhances the short circuit current. Furthermore, the open circuit voltage increases significantly mainly due to the constructive effect of the built-in electric field of the rear contact on the total built-in electric field of the solar cell. Dark current–voltage, capacitance–voltage and electrochemical impedance spectra are used to systemically investigate the influence of the PFN layer on the performance, with prospects of receiving a high efficiency device with the quality rear contact.

A Targeted and Stable Polymeric Nanoformulation Enhances Systemic Delivery of mRNA to Tumors

The high vulnerability of mRNA necessitates the manufacture of delivery vehicles to afford adequate protection in the biological milieu. Here, mRNA was complexed with a mixture of cRGD-poly(ethylene glycol) (PEG)-polylysine (PLys) (thiol) and poly(N-isopropylacrylamide) (PNIPAM)-PLys(thiol). The ionic complex core consisting of opposite-charged PLys and mRNA was crosslinked though redox-responsive disulfide linkage, thereby avoiding structural disassembly for exposure of mRNA to harsh biological environments. Furthermore, PNIPAM contributed to prolonged survival in systemic circulation by presenting a spatial barrier in impeding accessibility of nucleases, e.g., RNase, due to the thermo-responsive hydrophilic-hydrophobic transition behavior upon incubation at physiological temperature enabling translocation of PNIPAM from shell to intermediate barrier. Ultimately, the cRGD ligand attached to the formulation demonstrated improved tumor accumulation and potent gene expression, as manifested by virtue of facilitated cellular uptake and intracellular trafficking. These results indicate promise for the utility of mRNA as a therapeutic tool for disease treatment.

Tuning back contact property via artificial interface dipoles in Si/organic hybrid solar cells

Back contact property plays a key role in the charge collection efficiency of c-Si/poly(3,4-ethylthiophene):poly(styrenesulfonate) hybrid solar cells (Si-HSCs), as an alternative for the high-efficiency and low-cost photovoltaic devices. In this letter, we utilize the water soluble poly (ethylene oxide) (PEO) to modify the Al/Si interface to be an Ohmic contact via interface dipole tuning, decreasing the work function of the Al film. This Ohmic contact improves the electron collection efficiency of the rear electrode, increasing the short circuit current density (Jsc). Furthermore, the interface dipoles make the band bending downward to increase the total barrier height of built-in electric field of the solar cell, enhancing the open circuit voltage (Voc). The PEO solar cell exhibits an excellent performance, 12.29% power conversion efficiency, a 25.28% increase from the reference solar cell without a PEO interlayer. The simple and water soluble method as a promising alternative is used to develop the int...

Improved optical absorption in visible wavelength range for silicon solar cells via texturing with nanopyramid arrays

Surface-texture with silicon (Si) nanopyramid arrays has been considered as a promising choice for extremely high performance solar cells due to their excellent anti-reflective effects and inherent low parasitic surface areas. However, the current techniques of fabricating Si nanopyramid arrays are always complicated and cost-ineffective. Here, a high throughput nanosphere patterning method is developed to form periodic upright nanopyramid (UNP) arrays in wafer-scale. A direct comparison with the state-of-the-art texture of random pyramids is demonstrated in optical and electronic properties. In combination with the antireflection effect of a SiNx coating layer, the periodic UNP arrays help to provide a remarkable improvement in short-wavelength response over the random pyramids, attributing to a short-current density gain of 1.35 mA/cm2. The advanced texture of periodic UNP arrays provided in this work shows a huge potential to be integrated into the mass production of high-efficiency Si solar cells.

Evolution of tribo-induced interfacial nanostructures governing superlubricity in a-C:H and a-C:H:Si films

Hydrogenated amorphous carbon (a-C:H) is capable of providing a near-frictionless lubrication state when rubbed in dry sliding contacts. Nevertheless, the mechanisms governing superlubricity in a-C:H are still not well comprehended, mainly due to the lack of spatially resolved structural information of the buried contact surface. Here, we present structural analysis of the carbonaceous sliding interfaces at the atomic scale in two superlubricious solid lubricants, a-C:H and Si-doped a-C:H (a-C:H:Si), by probing the contact area using state-of-the-art scanning electron transmission microscopy and electron energy-loss spectroscopy. The results emphasize the diversity of superlubricity mechanisms in a-C:Hs. They suggest that the occurrence of a superlubricious state is generally dependent on the formation of interfacial nanostructures, mainly a tribolayer, by different carbon rehybridization pathways. The evolution of such anti-friction nanostructures highly depends on the contact mechanics and the counterpart material. These findings enable a more effective manipulation of superlubricity and developments of new carbon lubricants with robust lubrication properties.Hydrogenated amorphous carbon is a promising solid lubricant, but the underlying mechanisms surrounding its superlubricity remain unclear. Here the authors reveal that the attainment of a superlubricious state is dependent on the in-situin-situ formation of a nanostructured tribolayer through different carbon rehybridization pathways.

Controlled PEGylation Crowdedness for Polymeric Micelles To Pursue Ligand-Specified Privileges as Nucleic Acid Delivery Vehicles

A facile poly(ethylene glycol) (PEG) detachment scheme was utilized to control the PEGylation degree of the polymeric micelles. The performance of cyclic Arg-Gly-Asp (cRGD) as a targeted moiety was studied on a class of polymeric micelles with various PEGylation degrees, revealing that the specific cRGD-mediated cell affinity, thus the cellular uptake and implicated privileges including the ligand-specified favorable intracellular trafficking and consequent favorable biofunctions, was prominent for the polymeric micelles with high PEGylation degree. These results endow important information and implications for the design and development of targeted nanomedicine, particularly the delivery of vulnerable biological compounds.

In situ annealing and high-rate silicon epitaxy on porous silicon by mesoplasma process

By a mesoplasma process, a double-layer porous Si is annealed for a few seconds, by which an annealing effect similar to that of a prolonged conventional annealing process is obtained. The basic annealing process is considered to follow the classical sintering theory. However, the surface of the annealed porous Si is rough with large open voids because of H etching. The epitaxial Si films deposited on such a rough surface at a rate of 350 nm/s show a smooth surface with a low defect density compared with those deposited on a polished Si wafer, which clearly demonstrates the advantages of the cluster-assisted mesoplasma process.

Colloidal transfer printing method for periodically textured thin films in flexible media with greatly enhanced solar energy harvesting

The successful fabrication of high-performance flexible thin film solar cells (TFSCs) directly on diverse substrates is intrinsically limited by the processing temperature and substrate property. In this work, a colloidal transfer-printing (CTP) method is developed to fabricate large-area flexible thin-film absorbers with an antireflection coating and periodic configurations. Compared with a planar film, such structures exhibit much lower reflectance due to the antireflection introduced by the textured polydimethylsiloxane and the enhanced scattering introduced by the periodic back-scattering reflector. Optical simulation using the finite-element method indicates the structural periodicity for maximum light absorption is of 300 nm for an ultrathin amorphous silicon (a-Si) film with a thickness of 160 nm. The patterned a-Si film yields an overall absorption of 64.8%, which is much larger than the planar counterpart of 38.5%. This new approach to thin-film transfer can be readily extended to other material systems and device structures, opening up an effective alternative to traditional fabrication of the low-cost and high-performance optoelectronic devices.

Photoinduced Field-Effect Passivation from Negative Carrier Accumulation for High-Efficiency Silicon/Organic Heterojunction Solar Cells

Carrier recombination and light management of the dopant-free silicon/organic heterojunction solar cells (HSCs) based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) are the critical factors in developing high-efficiency photovoltaic devices. However, the traditional passivation technologies can hardly provide efficient surface passivation on the front surface of Si. In this study, a photoinduced electric field was induced in a bilayer antireflective coating (ARC) of polydimethylsiloxane (PDMS) and titanium oxide (TiO2) films, due to formation of an accumulation layer of negative carriers (O2- species) under UV (sunlight) illumination. This photoinduced field not only suppressed the silicon surface recombination but also enhanced the built-in potential of HSCs with 84 mV increment. In addition, this photoactive ARC also displayed the outstanding light-trapping capability. The front PEDOT:PSS/Si HSC with the saturated O2- received a champion PCE of 15.51% under AM 1.5 simulated sunlight illumination. It was clearly demonstrated that the photoinduced electric field was a simple, efficient, and low-cost method for the surface passivation and contributed to achieve a high efficiency when applied in the Si/PEDOT:PSS HSCs.

Band alignment of In2O3/β-Ga2O3 interface determined by X-ray photoelectron spectroscopy

The energy band alignment of the atomic-layer-deposited In2O3/β-Ga2O3 ( 2 ¯ 01) interface is evaluated by X-ray photoelectron spectroscopy. The X-ray diffraction pattern reveals that the In2O3 film grown at 160 °C is amorphous, while it becomes polycrystalline at a higher deposition temperature of 200 °C. The bandgaps, determined by reflection electron energy loss spectroscopy, are 4.65, 3.85, and 3.47 eV for β-Ga2O3, polycrystalline In2O3, and amorphous In2O3, respectively. Both amorphous and polycrystalline In2O3/β-Ga2O3 interfaces have Type I alignment. The conduction and valence band offsets at the polycrystalline (amorphous) In2O3/β-Ga2O3 interface are 0.35 and 0.45 eV (0.39 and 0.79 eV), respectively. These observations suggest that polycrystalline In2O3 as an intermediate semiconductor layer is beneficial to the barrier reduction of metal/Ga2O3 contact.The energy band alignment of the atomic-layer-deposited In2O3/β-Ga2O3 ( 2 ¯ 01) interface is evaluated by X-ray photoelectron spectroscopy. The X-ray diffraction pattern reveals that the In2O3 film grown at 160 °C is amorphous, while it becomes polycrystalline at a higher deposition temperature of 200 °C. The bandgaps, determined by reflection electron energy loss spectroscopy, are 4.65, 3.85, and 3.47 eV for β-Ga2O3, polycrystalline In2O3, and amorphous In2O3, respectively. Both amorphous and polycrystalline In2O3/β-Ga2O3 interfaces have Type I alignment. The conduction and valence band offsets at the polycrystalline (amorphous) In2O3/β-Ga2O3 interface are 0.35 and 0.45 eV (0.39 and 0.79 eV), respectively. These observations suggest that polycrystalline In2O3 as an intermediate semiconductor layer is beneficial to the barrier reduction of metal/Ga2O3 contact.