Pd-mediated mechanical stack of III–V solar cells fabricated via hydride vapor phase epitaxy

•Demonstration of mechanical stack of the cells grown by hydride vapor phase epitaxy.•III-V solar cells were bonded using Pd nanoparticles as the bonding mediator.•Conversion efficiency of 22.6% was achieved for the GaAs//InGaAs tandem cells. In this study, we present the first demonstration of mechanical stacking of solar cells grown via hydride vapor phase epitaxy (HVPE) to fabricate tandem cells. Smart stack technology, in which Pd nanoparticles were used as the bonding mediator, was used for bonding the cells. To prepare the smart stack, the top cells of the tandem structure were peeled from the substrate using the epitaxial lift-off technique. For this purpose, the cell structure was grown on an AlAs sacrificial layer. GaAs solar cells with good performance were fabricated using HVPE, in which the surface roughened by AlAs was restored to flatness by growing a thick GaAs film. The GaAs//InGaAs tandem cells achieved by bonding the GaAs solar cells grown via HVPE with the InGaAs solar cells grown by metal–organic vapor phase epitaxy exhibited a conversion efficiency of 22.6%.