@article{10902/29276,
year = {2018},
month = {2},
url = {https://hdl.handle.net/10902/29276},
abstract = {Germanium solar cells are used as bottom subcells in many multijunction solar cell designs. The question remains whether the thermal load originated by the growth of the upper layers of the multijunction solar cell structure affects the Ge subcell performance. Here, we report and analyze the performance degradation of the Ge subcell due to such thermal load in lattice-matched GaInP/Ga(In)As/Ge triple-junction solar cells. Specifically, we have detected a quantum efficiency loss in the wavelength region corresponding to the emitter layer (which accounts for up to 20% loss in equivalent JSC) and up to 55 mV loss in VOC of the Ge subcell as compared with analogous devices grown as single-junction Ge solar cells on the same type of substrates. We prove experimentally that there is no direct correlation between the loss in VOC and the doping level of the base. Our simulations show that both the JSC and VOC losses are consistent with a degradation of the minority carrier properties at the emitter, in particular at the initial nanometers of the emitter next to the emitter/window heterointerface. In addition, we also rule out the gradual emitter profile shape as the origin of the degradation observed. Our findings underscore the potential to obtain higher efficiencies in Ge-based multijunction solar cells if strategies to mitigate the impact of the thermal load are taken into consideration.},
organization = {This work has been supported by the European Commission through the LONGESST project (FP7 grant agreement no 607153), by the European Union's Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement no 656208, by the Spanish Ministerio de Economía y Competitividad through the projects TEC2014-54260-C3-1-P and TEC2015-66722-R, and from the Madrid local government under contract S2013/MAE-2780 (MADRID-PV). I García is funded by the Spanish “Programa Estatal de Promoción del Talento y su Empleabilidad” through a Ramón y Cajal grant. The authors would also like to thank Jesus Bautista for his continuous support and NREL for the processing and facilities for the measurement of the solar cells. This paper reflects only the author's view, and the funding agency is not responsible for any use that may be made of the information it contains.},
publisher = {Wiley-Blackwell},
publisher = {Progress in Photovoltaics: Research and Applications, 2018, 26(2), 102-111},
title = {Degradation of Ge subcells by thermal load during the growth of multijunction solar cells},
author = {Barrigón Montañés, Enrique and Ochoa Gómez, Mario and García Vara, Iván and Barrutia Poncela, Laura and Algora del Valle, Carlos and Rey-Stolle Prado, Ignacio},
}