III-V Nanomembranes for High Performance, Cost-Competitive Photovoltaics
- PDF / 641,207 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 18 Downloads / 161 Views
III-V Nanomembranes for High Performance, Cost-Competitive Photovoltaics Jongseung Yoon1 1 Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, CA 90089 USA ABSTRACT Due to their highly favorable materials properties such as direct bandgap, appropriate bandgap energy against solar spectrum, and ability to form multiple junctions, epitaxially grown III-V compound semiconductors such as gallium arsenide have provided unmatched performance over silicon in solar energy harvesting. However, their large-scale deployment in terrestrial photovoltaics remains as a daunting challenge mainly due to the high cost of growing devicequality epitaxial materials. In this regard, releasable multilayer epitaxial growth in conjunction with printing-based deterministic materials assemblies represents a promising approach that can overcome this challenge but also create novel engineering designs and device functionalities, each with significant practical values in photovoltaic technologies. This article will provide an overview of recent advances in materials design, fabrication concept, and nanophotonic light management of multilayer-grown nanomembrane-based GaAs solar cells aiming for high performance, cost-efficient platforms of III-V photovoltaics. INTRODUCTION III-V compound semiconductors such as GaAs represent materials of choice for ultrahigh efficiency solar cells due to excellent photophysical properties including direct and widely accessible bandgap energy, high electron mobility, and ability to form multiple junctions 1,2. Nevertheless, their practical usage in terrestrial photovoltaics have been limited by the excessive cost to prepare device-quality epitaxial materials 3. In this regard, epitaxial liftoff (ELO) has been invented as a promising approach to potentially provide significant cost reduction by reusing the growth wafer substrate 4,5. However, refinishing the growth wafer to restore epi-ready conditions involve multiple processing steps that can essentially degrade overall yield and costeffectiveness. EXPERIMENT Over the past years, an alternative approach of “releasable multilayer epitaxial assemblies” has been proposed to circumvent existing difficulties of ELO 6. In the multilayer epitaxial growth, multiple (e.g. dozens of) device stacks are grown on a single growth wafer in a single deposition step with lattice matched sacrificial layers inserted between device layers. This concept was first studied by growing triple-stack n-on-p type single junction GaAs solar cells. However, the performance of solar cells exhibited systematic degradation of short-circuit current density from top to bottom device layers (figure 1(a)) 6. According to the SIMS profile, the degraded performance was attributed to the diffusion of zinc in the middle and bottom device layers, which caused severe carrier compensation and modification of junction characteristics. More recently, triple-stack p-on-n type GaAs solar cells using carbon as a substitutional p-type dopant have been also st
Data Loading...
