Haruki Miyamoto

Mobile Solar Power

The militarys need to reduce both fuel and battery resupply is a real-time requirement for increasing combat effectiveness and decreasing vulnerability. Mobile photovoltaics (PV) is a technology that can address these needs by leveraging emerging, flexible space PV technology. In this project, the development and production of a semirigid, lightweight, efficient solar blanket with the ability to mount on, or stow in, a backpack and recharge a high-capacity rechargeable lithium-ion battery was undertaken. The 19% efficient blanket consists of a 10 × 3 solar array of 20 cm2 and single-junction epitaxial lift-off solar cells, which have an efficiency of ∼22% under AM1.5G illumination. A power-conditioning module was also developed to interface the solar panel to the battery. Thirteen systems were outfitted during a Limited Objective Experiment-1 in February 2012, and based on the results, a second version of the system is in development.

Flexible and lightweight epitaxial lift-off GaAs multi-junction solar cells for portable power and UAV applications

Epitaxial lift-off (ELO) is a process technology that can enable substantial performance enhancement and cost reduction for epitaxially grown III-V devices. [1]-[4] In particular, GaAs-based inverted metamorphic multijunction (IMM) solar cells are an attractive technology that provides flexible, light-weight and high-efficiency solar panels for portable-power and unmanned aerial vehicle (UAV) applications. ELO is a process that involves selectively etching a “release” layer to detach the epitaxially grown functional III-V material from the substrate on which it is grown. The flexible ELO solar cell device layers are temporarily mounted on rigid carriers for standard, high-volume semiconductor processing methods, followed by release and integration into flexible panel formats.

High efficiency flexible solar panels

The militarys need to reduce both fuel and battery resupply is a real time requirement for increasing combat effectiveness and decreasing vulnerability. Mobile photovoltaics (PV) are a technology that can address these needs by leveraging emerging, flexible space photovoltaic technology. In this ongoing project, the development and production of a semi-rigid, lightweight, efficient solar blanket with the ability to mount on, or stow in, a backpack and recharge a warfighters battery was undertaken. The blanket consists of a 10 × 3 solar array of 20 cm2 epitaxial lift-off (ELO) solar cells. In the first two phases of the project, single-junction cells with an efficiency of ~21% under AM1.5G illumination were used. Several of these systems were outfitted during Limited Objective Experiments (LOE) in February 2012 and August 2012. In the third and most current phase of this project, the panels will be made from IMM triple-junction cells with an efficiency of 28-30% under AM1.5G illumination. The results of laboratory tests of the new prototypes, as well as a test plan and expected outcome for a field experiment are presented here.

Niel analysis of radiation degradation parameters derived from quantum efficiency of triple-junction space solar cell

Degradation modeling of InGaP/GaAs/Ge triple-junction (3J) solar cells due to proton/electron irradiation is performed with the use of a one-dimensional optical device simulator; PC1D. By fitting external quantum efficiencies of the 3J solar cells degraded by proton/electron irradiation, the short-circuit currents (ISC) and open-circuit voltages (VOC) are simulated. The validity of this model is confirmed by comparing the results of both ISC and VOC to the experimental data. Then, the degradation level in each sub-cell is evaluated. The carrier removal rate of base layer (RC) and the damage coefficient of minority carrier diffusion length (KL) in each sub-cell are also estimated. In addition, NIEL (Non-Ionizing Energy Loss) analysis for both radiation degradation parameters RC and KL is discussed.

Current Injection Effects on the Electrical Performance of 3J Solar Cells Irradiated with Low and High Energy Protons

To compare high and low energy proton irradiation effects on the recovery behavior of triple-junction (3J) solar cells, 3J solar cells designed for space applications were irradiated with protons at 50 keV and 10 MeV, and their electrical performance was measured in situ under AM0 illumination. The electrical performance of the solar cells decreases with increasing proton fluence. For 50 keV-proton irradiation, the remaining factors of short circuit current (Jsc), open circuit voltage and maximum power become 81, 81 and 56 % respectively at a fluence of 1.2times1012/cm2. For 10 MeV-proton irradiation, these values are 83, 69 and 47 % at a fluence of 3times10 13/cm2. After proton irradiation, current injection into solar cells was performed at current densities between 0.03 and 0.25 A/cm2. The values of Jsc increase with increasing injected charge, and no significant difference in the increase behavior of Jsc is observed between 3J solar cells irradiated with 50 keV- and those irradiated with 10 MeV-protons. The obtained result suggests that the origin of defects annealed by current injection in 3J solar cells irradiated with protons at 50 keV is the same as that in 3J solar cells irradiated with protons at 10 MeV

Recovery of Short Circuit Current of 3J Solar Cells by Current Injection at Low Temperature

InGaP/GaAs/Ge triple-junction (3J) solar cells designed for space applications were irradiated with 10 MeV protons at 3times1013 /cm2 at 210 K. Current at 0.25 A/cm2 was injected into the irradiated 3J solar cells after irradiation at 210 K to avoid the thermal annealing effects. The short circuit current (Isc) recovered with increasing current injection time, and the recovery saturated at current injection times above 1000 sec. The saturated Isc was 98% of the initial value. The defect annealing rate (A) was estimated to be between 0.003 and 0.01/s from the fitting of the current injection time dependence of the recovery of I sc