Flexible Thin-Film Tandem Solar Cells With >30% Efficiency

Abstract

Alta Devices, Inc. has previously reported on singlejunction thin-film GaAs photovoltaic devices on flexible substrates with efficiencies up to 28.8% under AM1.5G solar illumination at 1-sun intensity. Here, we show that the same technology platform can be extended to tandem devices that are capable of even higher efficiencies: so far up to 30.8%. Specifically, here, we report on a lattice-matched, series-connected, two-junction device with InGaP as the light-absorbing material of the top cell and GaAs as the absorber in the bottom cell. The material is grown by metallorganic chemical vapor deposition, and then, the device is lifted off by the epitaxial liftoff (ELO) process, as previously reported. This demonstrates that ELO is not only capable of record-setting single-junction performance but capable of achieving world-class efficiency with a multijunction architecture as well.

High‐efficiency indium gallium nitride/Si tandem photovoltaic solar cells modeling using indium gallium nitride semibulk material: monolithic integration versus 4‐terminal tandem cells

“…In order to further increase the efficiency, we need to use multijunction solar cells. An efficiency that exceeds 30% has been already reported for tandem cell with III‐V materials over Gallium Arsenide (GaAs) . However, GaAs is expensive for terrestrial applications compared with silicon (Si).…”

Back reflectors based on buried Al2O3 for enhancement of photon recycling in monolithic, on-substrate III-V solar cells

“…[2][3][4] To deposit the metal layer(s) that form these reflectors, the back surface of the cell must be accessible. This can be accomplished by growing inverted devices and removing the substrate during processing, or by removing the substrate prior to the deposition of the metal.…”

Heterogeneously Integrated Optoelectronic Devices Enabled by Micro‐Transfer Printing

“…The schemes of epitaxial liftoff, first pioneered by Konagai et al in 1978, enable the release of active epitaxial materials from a growth wafer by selective wet chemical etching of a sacrificial layer . In the context of photovoltaics, the approach has been widely applied in various GaAs and InP based solar cells because of potential advantages in cost, arising from the substrate reuse and reduced materials consumption . Despite progress over the past three decades, however, conventional ELO has not emerged as an economically viable strategy due to many challenges including materials degradation in wafer recycling, low throughput in undercut etching, as well as difficulties in handling the released materials.…”