A Repeatable Epitaxial Lift‐Off Process from a Single GaAs Substrate for Low‐Cost and High‐Efficiency III‐V Solar Cells

Abstract

The effects of epitaxial materials and solar cell design on the performance of solar cells grown by the multilayer approach are investigated. The novel solar cell structure with a p‐on‐n type configuration suggested exhibits improved uniformity in the photovoltaic performance because of the suppression of Zn diffusion. This approach provides routes to achieve further improvements and acts as a guideline for the commercialization of the multilayer technique.

Heterogeneously Integrated Optoelectronic Devices Enabled by Micro‐Transfer Printing

“…Advances in processing and growth strategies have the potential, however, to improve the economics of III–V semiconductors in photovoltaics, and allow their competitive use in terrestrial systems. Recent work demonstrates that the concepts of transfer printing can be combined with single or multi‐layer epitaxial liftoff (ELO) schemes to yield promising paths to unique classes of ultrahigh concentration modules, where many existing issues for the cost‐competitive realization of III–V solar cells can be addressed . The following sections summarize advances in materials, fabrication, and transfer printing strategies for III–V compound semiconductor solar cells.…”

“…Many of these issues can be addressed by new ideas, coupled with the methods of transfer printing. A first example appears in Figure where the starting point is a thick, multilayer stack of device‐grade material epitaxially grown on a GaAs wafer by metal organic chemical vapor deposition (MOCVD), with compositions, thicknesses, and dopant characteristics of each layer selected to satisfy specific application requirements . Transfer printing allows the sequential retrieval of individual device layers following release by selective wet chemical etching of embedded sacrificial layers (e.g., AlAs for the case of GaAs).…”

“…The projected one‐sun (AM1.5D, 1000 W m −2 ) efficiencies of the multilayer‐grown GaAs solar cells based on the experimentally measured external quantum efficiency (EQE) and a double layer antireflection coating (e.g., MgF 2 /ZnS) are 20.5% and 19.5%, respectively, for devices formed with material from the top and middle layers of the stacks ( Figure ). Recent, alternative epitaxial designs eliminate mobile dopants, such as Zn, in the multilayer growth . For example, using carbon instead of Zn as a p‐type dopant in a ‘p‐on‐n’ configuration minimizes such effects .…”

“…For example, using carbon instead of Zn as a p‐type dopant in a ‘p‐on‐n’ configuration minimizes such effects . Further improvements in Zn‐doped triple‐stack assemblies are possible by exploiting Ga 0.50 In 0.50 P as a window and BSF layers in a p‐on‐n device configuration …”

“…As with silicon microcells, output characteristics of modules comprising printed arrays of GaAs microcells can be configured to meet the requirements of specific applications by adjusting the layouts of parallel‐ or series‐connected microcells . Mechanically bendable or stretchable modules are also possible by heterogeneously integrating collections of microcells onto thin sheets of plastic or slabs of microstructured rubber, respectively . As in the case of silicon, NMP designs reduce the bending induced strains in the GaAs in flexible modules ( Figure a) .…”