Multilayer-Grown Ultrathin Nanostructured GaAs Solar Cells as a Cost-Competitive Materials Platform for III–V Photovoltaics

Abstract

Large-scale deployment of GaAs solar cells in terrestrial photovoltaics demands significant cost reduction for preparing device-quality epitaxial materials. Although multilayer epitaxial growth in conjunction with printing-based materials assemblies has been proposed as a promising route to achieve this goal, their practical implementation remains challenging owing to the degradation of materials properties and resulting nonuniform device performance between solar cells grown in different sequences. Here we report an alternative approach to circumvent these limitations and enable multilayer-grown GaAs solar cells with uniform photovoltaic performance. Ultrathin single-junction GaAs solar cells having a 300-nm-thick absorber (i.e., emitter and base) are epitaxially grown in triple-stack releasable multilayer assemblies by molecular beam epitaxy using beryllium as a p-type impurity. Microscale (∼500 × 500 μm) GaAs solar cells fabricated from respective device layers exhibit excellent uniformity (<3% relative) of photovoltaic performance and contact properties owing to the suppressed diffusion of p-type dopant as well as substantially reduced time of epitaxial growth associated with ultrathin device configuration. Bifacial photon management employing hexagonally periodic TiO nanoposts and a vertical p-type metal contact serving as a metallic back-surface reflector together with specialized epitaxial design to minimize parasitic optical losses for efficient light trapping synergistically enable significantly enhanced photovoltaic performance of such ultrathin absorbers, where ∼17.2% solar-to-electric power conversion efficiency under simulated AM1.5G illumination is demonstrated from 420-nm-thick single-junction GaAs solar cells grown in triple-stack epitaxial assemblies.

Interplay of Photons and Charge Carriers in Thin-Film Devices

“…As such, they have not previously been reported due to the difficulty to simultaneously account for all underlying physical processes. We expect such spectrally and directionally resolved understanding of photon-recycling processes to be especially beneficial for understanding the internal electrical and optical properties of various thin-film devices, such as the emerging ultrathin GaAs photovoltaic devices [21][22][23][24], and to complement existing advanced modeling and characterization frameworks of multijunction solar cells [25,26].…”

Materials characterization by synchrotron x-ray microprobes and nanoprobes

“…Schematic representation of the different scattering, excitation, and decay phenomena that occur when an ion beam interacts with matter and the consequent IBA techniques: photon emissions [ionoluminescence, PIXE, and proton-induced or particle-induced γ-ray emission (PIGE), depending on the photon energy]; backscattered ions and nuclear reaction products in Rutherford backscattering spectroscopy (RBS) and nuclear reaction analysis (NRA), respectively; sputtered ions in secondary ions mass spectrometry (SIMS); and nuclei recoils in elastic recoil detection analysis (ERDA). results in the nuclear reaction analysis (NRA) technique which provides isotope specific elemental profiling especially sensitive to light elements such as hydrogen (Fukutani, 2002;Wilde and Fukutani, 2014). The depth sensitivity of NRA is obtained by changing the beam energy and thus its stopping power.…”

“…For more than four decades, the field of optoelectronic devices has been dominated by III-V heterostructures (Esaki, 1986;Cingolani and Ploog, 1991;Chang and Esaki, 1992;Alferov, 2001;Vurgaftman, Meyer, and Ram-Mohan, 2001;Mokkapati and Jagadish, 2009) because of their direct band gap. More recently, applications in high-efficiency solar cells have been realized (Cotal et al, 2009;Gai et al, 2017), while the possibility to realize CMOS devices with FIG. 16.…”

High‐efficiency photovoltaic modules on a chip for millimeter‐scale energy harvesting

“…We applied a monolithic PV module to demonstrate the perpetual operation of a millimeter‐scale wirelessly interconnected temperature logger system. Further improvements in millimeter‐scale PV module efficiency may be gained by continued improvement in reducing perimeter leakage current in small‐area cells and reduction in shunt leakage through techniques such as epitaxial layer transfer to fully insulating substrates or vertical multijunction designs …”