Seamless monolithic water splitting system using miniaturized crystalline silicon microwire interdigitated back contact photoelectrode

We fabricated c-Si based wireless monolithic artificial leaf for an efficient unassisted photoelectrochemical water splitting (PEC). A seamless module was manufactured using a c-Si interdigitated back contact (IBC) structure. Through modularization, a photoelectrode having an overpotential of 1.5 - 2 V or more was realized. So unassisted water splitting was possible. We fabricated a c-Si IBC photoanode that obtained an efficiency of 10.1 % at 0 V (unassisted water splitting). An artificial leaf, an unassisted-wireless water splitting system, was fabricated using the proposed c-Si IBC solar cell and showed about 8.4 % STH, which was the highest performance among the reported silicon-based wireless PEC systems despite no optimization of catalysts. The design suitable for artificial leaf devices and the expectation of improved efficiency through the development of catalysts make the c-Si IBC module artificial leaf system promising for the unassisted photoelectrochemical hydrogen production in practical application

Highly efficient radial-junction microwire solar cells by acid based doping process.

We propose a novel doping method to fabricate highly efficient radial-junction microwire solar cells using acid solutions (boric and phosphoric acids). Compared to the conventionally used toxic gas (POCl3 and BBr3) or polymer based (spin-on-dopant) doping sources, acid doping processes intrinsically have outstanding advantages such as high purity, non-toxic, and low cost process. High quality junctions for both emitter and back-surface-field (BSF) were successfully formed in the microwire solar cells using the acid doping processes. The measured minority carrier life time of microwire solar cells after the acid doping processes showed approximately three times higher value (66 us) compared to that after polymer based spin-on-doping process (23 us). Consequently, our best device with areas of 1 cm2 exhibited power conversion efficiencies (Eff) of up to 20% under AM 1.5G illumination. In particularly, the acid doping based solar cells showed notable increase (40 mV) in the open-circuit voltage (Voc) of 630 mV compared to that of spin-on-doping based solar cells (590 mV) due to the high purity of acid doping sources. This corresponds to an approximately 11.6 % increase in the Eff compared to that of spin-on-doping based solar cell (Eff = 18 %). Hence, we believe that the proposed acid doping processes would become a foundational technology for the development of highly efficient and cost-effective radial-junction solar cells

Natural leaf-inspired solar water splitting system

We designed a monolithic artificial leaf that mimics a natural leaf; the artificial leaf has a crystalline silicon (c-Si) interdigitated back contact (collectively, c-Si IBC) structure. On the front-side of the artificial leaf, the c-Si module acts similar to chlorophyll in natural leaves, converting solar energy into photo-carriers. On the rear-side of the artificial leaf, a hydrogen and oxygen evolution catalyst converts the carriers into hydrogen; this occurs without blocking light, similar to the conversion of photo-carriers into chemical energy, which mostly occurs on the backside of natural leaves. The solar-to-hydrogen conversion efficiency of the c-Si IBC photoanode and artificial leaf was 10.1% and 8.4% respectively, which are higher than that of a natural leaf (0.1-1%)

Synthesis of Thermally Stable Reactive Polyurethane and Its Physical Effects in Epoxy Composites

A flame retardant polyol (EP-DOPO) with epoxy functional groups was synthesized by reacting a 1,6-hexanediol glycidyl ether with a flame retardant 10-(2,5-dihydroxyphenyl)-10H-9-oxa-10-phospha-phenanthrene-10-oxide (DOPO). The polyurethane (EPPU) with enhanced heat resistance was prepared by the reaction of a polyol blend of EP-DOPO and polytetrahydrofuran (PolyTHF) at a ratio of 1:1 with isophorone diisocyanate. EPPU useful for the preparation of cables or coatings showed higher thermal decomposition temperature rather than that of reference polyurethane synthesized by the reaction between pure PolyTHF and isophorone diisocyanate by thermogravimetric analysis. Further study of the polyurethane as a toughening agent for epoxy polymers was carried out. Epoxy compositions consisting of bisphenol A epoxy resin and dicyandiamide as a hardener have a brittle property allowing crack propagation after cure. Polyurethane plays an important role as an impact modifier to prevent from cracks of epoxy polymers. Various contents of EPPU were added into epoxy compositions to measure the physical property changes of epoxy polymers. The tensile and flexural strengths of the cured specimen were compared with those of epoxy compositions including reference polyurethane. Furthermore, the crosslink density of the cured epoxy compositions was compared

Thermally Cross-Linkable Diamino-Polyethylene Glycol Additive with Polymeric Binder for Stable Cyclability of Silicon Nanoparticle Based Negative Electrodes in Lithium Ion Batteries

We developed a new type of additive with poly(acrylic acid) (PAA) for stable cycling retention of silicon anodes. Diamino-Polyethylene Glycol (diamino-PEG) is used as a thermally curable additive with PAA polymeric binder for silicon nanoparticle based negative electrodes. Amino groups of the diamino-PEG form amide bonds with carboxylic acid groups of the PAA binder, which gives strong binding force even under high humidity. The highly cross linked amide bonds between diamino-PEG and PAA binder in silicon nanoparticle based negative electrodes leads to reduced electrical contact loss of silicon particles during electrochemical reaction. It also supports stable cycling performance and enhances specific capacity compared to the case of using only a silicon anode PAA binder.clos

Synthesis of Waterborne Polyurethane Using Phosphorus-Modified Rigid Polyol and its Physical Properties

In this study, a phosphorous-containing polyol (P-polyol) was synthesized and reacted with isophorone diisocyanate (IPDI) to produce water-dispersed polyurethane. To synthesize waterborne polyurethanes (WPUs), mixtures of P-polyol and polycarbonate diol (PCD) were reacted with IPDI, followed by the addition of dimethylol propionic acid, to confer hydrophilicity to the produced polyurethane. An excess amount of water was used to disperse polyurethane in water, and the terminal isocyanate groups of the resulting WPUs were capped with ethylene diamine. P-polyol:PCD molar ratios of 0.1:0.9, 0.2:0.8, and 0.3:0.7 were used to synthesize WPUs. The films prepared by casting and drying the synthesized WPUs in plastic Petri dishes were used to test the changes in physical properties induced by changing the P-polyol:PCD molar ratio. The experimental results revealed that the tensile strength of PU-10, the WPU with a P-polyol:PCD molar ratio of 0.1:0.9, was 16% higher than that of the reference P-polyol–free WPU sample. Moreover, the thermal decomposition temperature of PU-10 was 27 °C higher than that of the reference sample