100-period, 1.23-eV bandgap InGaAs/GaAsP quantum wells for high-efficiency GaAs solar cells: toward current-matched Ge-based tandem cells

Abstract

Major challenges for InGaAs/GaAsP multiple quantum well (MQW) solar cells include both the difficulty in designing suitable structures and, because of the strain-balancing requirement, growing high-quality crystals. The present paper proposes a comprehensive design principle for MQWs that overcomes the trade-off between light absorption and carrier transport that is based, in particular, on a systematical investigation of GaAsP barrier effects on carrier dynamics that occur for various barrier widths and heights. The fundamental strategies related to structure optimization are as follows: (i) acknowledging that InGaAs wells should be thinner and deeper for a given bandgap to achieve both a higher absorption coefficient for 1e-1hh transitions and a lower compressive strain accumulation; (ii) understanding that GaAs interlayers with thicknesses of just a few nanometers effectively extend the absorption edge without additional compressive strain and suppress lattice relaxation during growth; and (iii) understanding that GaAsP barriers should be thinner than 3 nm to facilitate tunneling transport and that their phosphorus content should be minimized while avoiding detrimental lattice relaxation. After structural optimization of 1.23-eV bandgap quantum wells, a cell with 100-period In 0.30 GaAs(3.5 nm)/GaAs(2.7 nm)/GaAsP 0.40 (3.0 nm) MQWs exhibited significantly improved performance, showing 16.2% AM 1.5 efficiency without an anti-reflection coating, and a 70% internal quantum efficiency beyond the GaAs band edge. When compared with the GaAs control cell, the optimized cell showed an absolute enhancement in AM 1.5 efficiency, and 1.22 times higher efficiency with 38% current enhancement with an AM 1.5 cut-off using a 665-nm long-pass filter, thus indicating the strong potential of MQW cells in Ge-based 3-J tandem devices.

Quantum wells for high-efficiency photovoltaics

“…Finally, it has been suggested above that a large number of QWs should provide a higher absorption and therefore higher photocurrent 27,28 However, it is also found that the open circuit voltage decreases with the number of wells due to higher non-radiative dark current, balancing the benefits of including more QWs 29 . This effect would be more severe for deep or lower quality QWs, when dark current is higher and mobilities, lower.…”

“…Fujii et al reported in 2013 a MQW structure with 100 periods, a QE of near 75% and with an absorption edge at 1.23 eV 27 . Their performance as a solar cell when illuminated with filtered light (E<1.86 eV) showed an I sc = 12.1 mA/cm 2 , V oc =0.823 and FF=74.6%.…”

Low-temperature MOVPE using TEGa for suppressed layer undulation in InxGa1−xAs/GaAs1−yPy superlattice on vicinal substrates

“…These devices have been demonstrated mostly on GaAs substrates, but high-quality InGaAs/GaAsP SLs are required to be grown on Ge substrates for Ge-based devices as multi-junction solar cells [12,13]. Substituting GaAs substrates with Ge substrates can also simply contribute to cost reduction.…”

Оптические Свойства Гибридных Наноструктур "Квантовая Яма-Точки", Полученных Методом Мос-Гидридной Эпитаксии

“…[2][3][4] и демонстрируют качественно улучшенные характеристики по сравнению с приборами на объемных слоях. При этом ввиду малой толщины слоев КЯ их можно выполнять из материалов не согласованных по параметру решетки с подложкой без релаксации упругих напряжений.…”