Tetsuya Asano

A Novel Thin Concentrator Photovoltaic With Microsolar Cells Directly Attached to a Lens Array

We propose a novel concept of thin and compact CPV modules in which submillimeter solar cells are directly attached to lens arrays without secondary optics or an extra heat sink. With this small cell size, the optical path length of the module can be brought down to one-twentieth that of conventional CPV modules. To achieve precise alignment of the microsolar cells at the lens focal points, we have developed a fluidic self-assembly technique that utilizes surface tension. This novel CPV module with triple junction microsolar cells demonstrated an efficiency of 34.7% under sunlight in the particular measured condition.

High efficiency micro solar cells integrated with lens array

We demonstrate high efficiency triple junction solar cells with submillimeter dimensions in an all-back-contact architecture. 550 × 550 μm2 cells flash at 41.3% efficiency under the air mass 1.5 direct normal spectrum at 50 W/cm2 at 25 °C. Compared to standard size production cells, the micro cells have reduced performance at 1-sun due to perimeter recombination, but the performance gap closes at higher concentrations. Micro cells integrated with lens arrays were tested on-sun with an efficiency of 34.7%. All-back-contact architecture and submillimeter dimensions are advantageous for module integration and heat dissipation, allowing for high-performance, compact, lightweight, and cost-effective concentrated photovoltaic modules.

High-efficiency thin and compact concentrator photovoltaics using micro-solar cells with via-holes sandwiched between thin lens-array and circuit board

We have developed a compact concentrator photovoltaic (CPV) module that comprises micro-solar cells with an area of ≈0.6 × 0.6 mm2 sandwiched between a 20-mm-thick lens array and a 1-mm-thick circuit board with no air gap. To establish electrical connections between the circuit board and the micro-solar cells, we developed a micro-solar cell with positive and negative electrodes on the lower face of the cell. In this study, we demonstrated the photovoltaic performance of the micro-solar cell closely approaches that of the standard solar cell measuring ≈5 × 5 mm2 commonly used in conventional CPVs under concentrated illumination. Our study showed that the negative effect on PV performance of perimeter carrier recombination in the micro-solar cell was insignificant under concentrated illumination. Finally, we assembled our micro-solar cells into a CPV module and achieved the module energy conversion efficiency of 34.7% under outdoor solar illumination.

Conductivity Modulation of Gold Thin Film at Room Temperature via All-Solid-State Electric-Double-Layer Gating Accelerated by Nonlinear Ionic Transport

We demonstrated the field-effect conductivity modulation of a gold thin film by all-solid-state electric-double-layer (EDL) gating at room temperature using an epitaxially grown oxide fast lithium conductor, La2/3-xLi3xTiO3 (LLT), as a solid electrolyte. The linearly increasing gold conductivity with increasing gate bias demonstrates that the conductivity modulation is indeed due to carrier injection by EDL gating. The response time becomes exponentially faster with increasing gate bias, a result of the onset of nonlinear ionic transportation. This nonlinear dynamic response indicates that the ionic motion-driven device can be much faster than would be estimated from a linear ionic transport model.

Solid Halide Electrolytes with High Lithium‐Ion Conductivity for Application in 4 V Class Bulk‐Type All‐Solid‐State Batteries

New lithium halide solid-electrolyte materials, Li3 YCl6 and Li3 YBr6 , are found to exhibit high lithium-ion conductivity, high deformability, and high chemical and electrochemical stability, which are required properties for all-solid-state battery (ASSB) applications, particularly for large-scale deployment. The lithium-ion conductivities of cold-pressed powders surpass 1 mS cm-1 at room temperature without additional intergrain or grain boundary resistances. Bulk-type ASSB cells employing these new halide solid electrolyte materials exhibit coulombic efficiencies as high as 94% with an active cathode material of LiCoO2 without any extra coating. These superior electrochemical characteristics, as well as their material stability, indicate that lithium halide salts are another promising candidate for ASSB solid electrolytes in addition to sulfides or oxides.

A biomimetic strategy for designing easily-installable CPV tracking system with high wind resistivity

Due to its higher photovoltaic efficiency, CPV has the advantage of needing a smaller panel footprint than fixed PV systems. This characteristic makes it ideal for use as an independent power supply in remote locations where transportation and site procurement present a challenge. The overall system needs to be compact and light without sacrificing weather resistance. Skilled personnel are scarce in remote areas, so easy setup and maintenance are also important. We have developed two techniques based on the notion of bio-mimicry. One is machine learning to counteract errors in installation position without the need for human intervention, and the other is a three-dimensional panel structure that cuts the wind load by up to 20%. We describe our experimental results gained in field tests.