This paper shows a new semiconductor bonding technology for mechanically stacked multi-junction solar cells. Our strategy is the combination of conductive nanoparticle alignments and the van der Waals bonding technique. With this method, reasonably low bonding resistances and minimal optical absorption losses were simultaneously attained for the use of mechanically stacked solar cells. We examined a GaInP(Eg-1.89 eV)/GaAs (Eg-1.42 eV)/InGaAsP (Eg-1.15 eV) three-junction solar cell fabricated with this bonding method. As a result, the total efficiency of 22.5% was achieved, which was in good agreement with the theoretically predicted value. These results suggested that our bonding method is highly useful to fabricate high-efficiency mechanically stacked multi-junction solar cells.

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Hydride vapor phase epitaxy (HVPE) is a III–V device fabrication technology that has received attention owing to its low production costs. The properties of passivation layers used to reduce surface and interface recombination losses in III–V materials considerably contribute to the performance of various devices. Herein, solar cells based on AlInGaP back‐surface field (BSF) layers grown via HVPE using aluminum trichloride as the group‐III precursor for Al deposition are presented. Although high‐concentration Si contamination occurs in Al‐containing layers grown using HVPE, AlInGaP with p‐type conductivity can be grown by doping with high‐concentration Zn. For InGaP single‐junction solar cells, the short‐circuit current density and open‐circuit voltage are improved by introducing the AlInGaP BSF layer. Consequently, the InGaP single‐junction solar cells measured under air mass 1.5 global solar spectrum illumination achieve a conversion efficiency of 17.1%. Furthermore, the progress in the development of tandem solar cells grown using HVPE is reported. By improving the performance of the InGaP top cells, InGaP/GaAs tandem cells are fabricated with a new record efficiency of 28.3% using the triple‐chamber HVPE system.

Hydride vapor phase epitaxy (HVPE) is a promising technique for fabricating low-cost III–V solar cells. This letter highlights the fast growth of InGaP single-junction solar cells via HVPE. High-quality InGaP layers without decomposition are obtained at a growth temperature of 660 °C. InGaP growth rate increases with increasing gaseous hydrogen chloride (HCl) flow rate to group III metals. Herein, the highest rate of 54 μm h−1 is achieved on InGaP growth. Furthermore, InGaP single-junction solar cells grown with high growth rate exhibit good performance under an air mass 1.5 global solar spectrum.