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

作者：Toprasertpong Kasidit^*; Fujii Hiromasa; Thomas Tomos; Fuehrer Markus; Alonso Alvarez Diego; Farrell Daniel J; Watanabe Kentaroh; Okada Yoshitaka; Ekins Daukes Nicholas J; Sugiyama Masakazu; Nakano Yoshiaki

来源：Progress in Photovoltaics: Research and Applications , 2016, 24(4): 533-542.

DOI：10.1002/pip.2585

• quantum well
• strain compensation
• lattice match
• multijunction subcell
• bandgap engineering
• III-V semiconductors

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 1.31eV to as low as 1.15eV. The bandgap-voltage-offset of MQWs is found to be independent of effective bandgaps and superior to a bulk reference by approximately 0.1V. 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.

• 出版日期2016-4