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The impact of 1 MeV proton irradiation on 1.12 eV bandgap InGaAsN solar cells was studied through device and material characterizations. After a 10 13 p + cm −2 proton fluence, the photocurrent decreases by 28%, due to the formation of defects in both the GaAs emitter and the InGaAsN absorber. Furthermore, photoluminescence measurements suggest that the proton radiation hardness of InGaAsN increases with the nitrogen.

In certain configurations, solar cells are operating under thermal stress, i.e. at temperatures far beyond those of the Standard Test Conditions (STC, 25 °C) [1]. In space for near-the-sun missions [2] or in terrestrial photovoltaic -thermal [3] or -thermoelectric [4] or CSP [5] hybrid systems, cells can reach temperatures from 150 °C up to more than 400 °C. New methodologies aiming at designing, fabricating and characterizing such components are required. The main unknowns are the physical properties of the materials involved and the physical phenomena affecting the photovoltaic conversion performances of cells at such large temperatures. To contribute to addressing these unknowns, our research work consists in analyzing the performances of conventional GaAs solar cells - optimized in the STC -, but operating under thermal stress (at up to 200 ᵒC). Such cells are fabricated using solid source Molecular Beam Epitaxy and conventional clean room processes, and their performances are characterized by measuring the I-V curves in the dark and under illumination, the spectral response, and the reflectance of the cells as a function of temperature, from 25 to 200 °C. Factors responsible for the expected degradation of performances with temperature are analyzed using TCAD 1D-simulations and pseudo-3D modeling [6]. The temperature sensitivity of carrier mobilities and contact resistances are examined by Hall effect and CTLM measurements (Figure 1). In particular, we show that the reliability of the methodology for characterizing the contacts is strongly dependent on the number and quality of the samples. Therefore, we propose a novel approach which eliminates some usual simplifying assumptions and considers the propagation of measurement errors by using a Monte Carlo technique (Figure 1-2).

In this article, we investigate the molecular beam epitaxy growth of unannealed 1.12 eV InGaAsN solar cells. The impact of the growth temperature, the As/III ratio and the bismuth used as a surfactant are reported. An in-situ curvature measurement setup enables to monitor and ensures a constant N incorporation during the InGaAsN growth. Ex-situ characterization results suggest that a high As/III ratio ensures good optoelectronic properties and that the growth temperature has a strong influence on the residual doping of the dilute nitride layer. Under AM0 > 870 nm and without antireflection coatings, our best InGaAsN solar cells exhibit J(sc) and V-oc values of 7.94 mA/cm(2) and 0.375 V, respectively. Considering no internal reflection and no grid shading, generation up to 12 mA/cm(2) in a multijunction solar cell can be expected, which is the highest value ever reported for As-grown InGaAsN cells to our knowledge.

Probing in real time thin film processes is an efficient way to unravel the impact of key parameters as this approach offers a direct insight on the involved mechanisms. MBE has benefited from a large number of in-situ techniques like RHEED, reflectivity, or optical thermometry. Despite the direct measurement of stress in the growing layers that they allow, curvature measurement tools based on laser deflectometry have not been widely adopted by the MBE community, due to intrinsic technological limitations. We have developed a novel curvature measurement technique, named Magnification Inferred Curvature (MIC), that overcomes these limitations. We will explain the principle of the measurement and illustrate its unique capabilities with a few selected examples, focusing on the GaAs1-xBix alloy. Keywords: in-situ, curvature, stress, dilute bismide

The degradation of InGaAsN p-i-n subcell under 1-MeV electron irradiation was studied by characterizing solar cells and dilute nitride bulk layers before and after irradiation. Cells are measured to retain more than 94% of their original photocurrent after 10 15 cm -2 , 1-MeV electron irradiation. Moreover, no significant degradation of the optoelectronic properties is observed after irradiation.

This paper reports on the optimization of 1 eV dilute nitride solar cells growth conditions. InGaAsN cells were grown by MBE under different conditions (V/III ratio, substrate temperature, surfactant) and were processed without post-growth annealing. Characterization results suggest that the V/III ratio should be kept above 10 and that using Bi as a surfactant does not improve the cell performances. Our best InGaAsN cells exhibit J sc and V oc values of 7.9 mA/cm 2 and 0.375 V respectively, under nm and without ARC.