Absorption threshold extended to 1.15 eV using InGaAs/GaAsP quantum wells for over‐50%‐efficient lattice‐matched quad‐junction solar cells

Abstract

Bandgap engineering of strain-balanced InGaAs/GaAsP multiple quantum wells (MQWs) allows high-quality materials with an absorption edge beyond GaAs to be epitaxially grown in Ge/GaAs-based multijunction solar cells. We demonstrate MQW solar cells with effective bandgaps ranging from 1.31 eV to as low as 1.15 eV. The bandgap-voltage-offset of MQWs is found to be independent of effective bandgaps and superior to a bulk reference by approximately 0.1 V. This implies the merit of high photovoltage as compared with bulk cells with the same bandgap in addition to their widely bandgap-tunable property. Towards the realization of fully lattice-matched quad-junction devices, we demonstrate a 70-period, 1.15-eV bandgap MQW cell as a promising material in 0.66/1.15/1.51/1.99-eV quad-junction cells, whose practical efficiency has a potential to achieve over 50%. With such a large period number of MQWs, the reverse-biased external quantum efficiency reaches an average of over 60% in the spectral region corresponding to a 1.15-eV subcell; this is achieved with only a-few-percent drop at short-circuit condition. The device presented here reaches the target open-circuit voltage and over 75% of the current density required for realizing a 1.15-eV subcell in a 50%-efficient quad-junction solar cell. We believe that future devices which exploit light-trapping structures and enhanced carrier extraction will be able to reach the desired target.

Impact of in-situ annealing on dilute-bismide materials and its application to photovoltaics

“…For the current device structures, the base region was measured to be p-type with the background concentration as high as − × − 1 2 10 cm 19 3 from the electrochemical capacitance voltage measurement. The second factor can be addressed by strain compensation, employing tensile-strained GaAs 1À y P y barriers [8], which allow for the increased thickness of the base region, as reported in the context of InGaAs/GaAsP MQW solar cells [19][20][21]. For the best extraction of the electron and hole pairs generated in the based region, the GaAsP thickness has to be thin enough with high P fraction so that there is weak electron-hole confinement in the QW, allowing the formation of minibands Intensity (a.u.…”

Recent results for concentrator photovoltaics in Japan

“…5(a). 7) It has been predicted that, when incorporated in a four-junction solar cell, a QW with this bandgap can lead to solar cells with efficiencies above 50%, as shown Fig. 5(b).…”

Development of back side technology for light trapping and photon recycling in GaAs solar cells

“…Multi‐junction solar cells can also benefit from photon management through luminescence coupling amongst its junctions and photon recycling effects which would ultimately improve energy conversion efficiency by better current matching conditions and V OC increase . Photon management also brings advantages to nanostructured devices in which several repetitions of active layers of quantum wells or quantum dots are commonly necessary to boost optical properties . Furthermore, as a general benefit of photon management, cost of materials can also be reduced.…”