Search

Passivation capping that enhances the photoluminescence (PL) of molecular beam epitaxy (MBE)-grown InAs surface quantum dots (SQDs) is realized by ex situ low-temperature atomic layer deposition (ALD)-grown Al2O3. As the Al2O3 cap thickness increased from 2 to 30 nm, the PL intensity was enhanced by 2.7-fold and the blue shift was suppressed. This is in strong contrast to wet chemistry passivation and in situ GaAs capping by MBE, both of which resulted in significant PL blueshift, due to etching in the former, and In/Ga intermixing and strain in the latter. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) reveal that the Al2O3 cap layer mimics the shape of the underlying SQDs. The cross-sectional transmission electron microscopy (TEM) further reveals that the SQD size and shape remained unchanged after Al2O3 capping, which is in strong contrast to MBE-capping. The passivation mechanisms and native oxide reduction by trimethylaluminum (TMA), including self-clean-up reaction through ligand exchange, are discussed based on the results by x-ray photoelectron spectroscopy (XPS). A detailed comparison between Al2O3 and ZnO cap layers reveals the significance of the cap properties on the SQD size/shape and PL blueshift. While the size/shape of SQDs is preserved by Al2O3 capping, the apex is slightly removed by ZnO capping, resulting in a stronger PL blueshift compared to Al2O3. [ABSTRACT FROM AUTHOR]

The development of the vehicles powered by photovoltaic (PV) is desirable and very important for reducing CO2 emissions from the transport sector to realize a decarbonized society. Although long‐distance driving of vehicle‐integrated PV (VIPV)‐powered vehicles without electricity charging is expected in sunny regions, driving distance of VIPV‐powered vehicles is affected by climate conditions such as solar irradiation and outside temperature, and the power consumption of the air conditioners. In this article, analytical results for system efficiency of VIPV‐powered vehicles and the effects of usage of air conditioner are presented by using power losses estimated from the electric mileage by using the driving distance data for Toyota Prius and Nissan Van demonstration cars installed with high‐efficiency InGaP/GaAs/InGaAs three‐junction solar cell modules with a module efficiency of more than 30%. The potential of VIPV‐powered vehicles to be deployed in major cities in Japan and the world is also analyzed. Mild weather cities such as Miyazaki in Japan and Sydney in Australia are thought to have longer driving range even under usage of air conditioners. The other power losses for the VIPV such as temperature rise of VIPV modules and partial shading estimate the previous data and some reference as well as effects of usage of air‐conditioners are also discussed in this article. [ABSTRACT FROM AUTHOR]

The development of high-performance solar cells offers a promising pathway toward achieving high power per unit cost for many applications. Because state-of-the-art efficiencies of single-junction solar cells are approaching the Shockley-Queisser limit, the multi-junction (MJ) solar cells are very attractive for high-efficiency solar cells. This paper reviews progress in III–V compound single-junction and MJ solar cells. In addition, analytical results for efficiency potential and non-radiative recombination and resistance losses in III–V compound single-junction and MJ solar cells are presented for further understanding and decreasing major losses in III–V compound materials and MJ solar cells. GaAs single-junction, III–V 2-junction and III–V 3-junction solar cells are shown to have potential efficiencies of 30%, 37% and 47%, respectively. Although in initial stage of developments, GaAs single-junction and III–V MJ solar cells have shown low ERE values, ERE values have been improved as a result of several technology development such as device structure and material quality developments. In the case of III–V MJ solar cells, improvements in ERE of sub-cells are shown to be necessary for further improvements in efficiencies of MJ solar cells.

The spread of the photovoltaic‐powered electric vehicle (PV‐EV) is desirable and is essential for reduction in CO2 emissions, increasing electric range, and creating a new clean energy infrastructure based on PVs. Development of highly efficient PV modules with reasonable cost is necessary to realize a longer PV‐driving range of passenger cars. Herein, the potential of various solar cell modules for vehicle‐integrated photovoltaic (VIPV) applications is analyzed. This article shows that the use of highly efficient solar cell modules with an efficiency of higher than 35% enables longer than 30 km day−1 PV driving under average irradiance of 4 kWh m−2 day−1 without external charging. Cost reduction of VIPV modules is also very important for spreading the PV‐powered vehicles. By considering electricity charging cost saving and reduction in CO2 emission of electric vehicles, the cost target of VIPV is discussed. The cost targets of the solar cell modules for the PV‐EV by considering only electricity charging cost saving, $2.6/Wp for a module with conversion efficiency of 20% and $3.7/Wp for a module with that of 40%, are estimated in the case of electric mileage of 10 km kWh−1. [ABSTRACT FROM AUTHOR]