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We report on integration of wavelength selective photonic structures (WSPS) such as distributed bragg reflectors (DBR) and multi quantum well structures to InGaP-GaAs dual junction (DJ) and GaAs single junction (SJ) solar cells. Epitaxial lift Off (ELO) process compatible InAlP-InGaP DBR structures and strain balanced GaAsP-InGaAs MQW developed. Subcell voltages for DJ cells were extracted from EL measurements. EQE data for GaAs sub cells was modeled and compared with experimental data. 1MeV Electron radiation studies performed to evaluate the radiation hardness of these ELO DJ cells with integrated DBR exhibited 12% improvement in remaining factor P/P 0 values (EoL performance for 1E15 electron irradiation) when compared with baseline DJ cell with no DBR.

Reducing the thickness of the GaAs absorber in a multijunction solar cell can increase radiation tolerance, while incorporation of a distributed Bragg reflector (DBR) can maintain current density by maintaining optical path length. In a closely current matched multijunction design, low energy sidelobe reflections of the DBR parasitically affect the subcell below the GaAs junction. A variation of the DBR design is proposed to mitigate this loss mechanism by maximizing transmission below the main Bragg peak. Through simulated multijunction and experimental verification of test structures, this paper will show how this “longpass” DBR can be optimized to improve current matching while maintaining radiation hardening afforded by thinning the GaAs junction.

In this work, textured back surface reflectors (BSR) produced by inverse progression metal-assisted chemical etching (I-MacEtch) is used to render wavelength-specific (WS) light trapping structures for thin GaAs solar cells. The HAZE reflectance measured on the MacEtch BSR shows 80% HAZE in the GaAs absorbing region indicative of high diffused photon scattering. The MacEtch BSR was implemented in a 500 nm thick GaAs solar cell, and the external quantum efficiency shows a 17% enhancement in the photogenerated carrier collection from the base of the solar cell when compared to the flat BSR device. The Fabry-Perot EQE fringes show a photon lifetime enhancement factor of 5.7 in the MacEtch BSR device, especially evident near the GaAs band edge. The recovered photoabsorption provides evidence that the WS BSR can be implemented into a dual-junction InGaP/GaAs solar cell to provide high current output in a radiation-tolerant thinned GaAs subcell.