Department of Electrical Engineering, Yale University , New Haven, Connecticut 06520, United States.
Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
ACS Nano. 2017 Jan 24;11(1):992-999. doi: 10.1021/acsnano.6b07605. Epub 2017 Jan 11.
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.
在地面光伏中大规模部署砷化镓太阳能电池需要大幅降低制备器件质量外延材料的成本。尽管结合印刷基材料组件的多层外延生长已被提出作为实现这一目标的有前途的途径，但由于材料性能的退化和不同生长顺序的太阳能电池之间不均匀的器件性能，其实际实施仍然具有挑战性。在这里，我们报告了一种替代方法来规避这些限制，并实现具有均匀光伏性能的多层生长砷化镓太阳能电池。使用分子束外延技术，通过在三重可释放多层组件中外延生长超薄的 300nm 厚的单结砷化镓太阳能电池（即发射极和基极），并使用铍作为 p 型杂质。由于 p 型掺杂剂的扩散得到抑制以及与超薄器件结构相关的外延生长时间大大减少，因此由各自的器件层制造的微尺度（约 500×500μm）砷化镓太阳能电池表现出优异的光伏性能和接触性能均匀性（<3%相对）。采用六边形周期性 TiO 纳米柱和垂直 p 型金属接触作为金属背面反射器的双面光子管理以及专门的外延设计，最大限度地减少寄生光学损耗，以实现高效光捕获的协同作用，从而显著提高了这种超薄吸收体的光伏性能，其中在模拟 AM1.5G 照明下，从生长在三重堆栈外延组件中的 420nm 厚单结砷化镓太阳能电池中获得了约 17.2%的太阳能到电能的转换效率。
