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In this work, we propose and realize three different design strategies to implement an optical cavity in GaAs thin film solar cells in order to confine its internal luminescence and hence to exploit photon recycling. The strategies are based on the definition of a highly reflective and very conductive back side, whereas front side light extraction is limited by total internal reflection. We show characterization results on the internal reflectivity of the back reflector and on the contact resistance at the rear side, important quantities for a good functioning of the final solar cell. First, a back side using only metal was optimized with a pure Ag layer leading to an internal reflectivity of 95.2% and a contact resistance of 1.0 × 10−4 Ω for a 1 cm2 device. With a metal‐dielectric stack at the back side and electrical contacts made by metals via point‐contacts, a second approach led to averaged internal reflectivity of 98.0% and contact resistance of 1.8 × 10−4 Ω for a 1 cm2 device. A third strategy in which a transparent conductive oxide in combination with a metal layer was used did not show the expected results in optical and electrical properties. We fabricated and characterized solar cells with the most promising back sides. When comparing with an ordinary reference GaAs solar cell, external radiative efficiency increased by factors of 150% and 90% for the thin film solar cells with pure Ag and with the metal‐dielectric stack at the back side, allowing enhancements of 19 and 13 mV in VOC, respectively.

Articles you may be interested inInGaAs/GaAsP superlattice solar cells with reduced carbon impurity grown by low-temperature metal-organic vapor phase epitaxy using triethylgallium J. Appl. Phys. 116, 203101 (2014)

In this work, we revisit the theoretical study on the conversion efficiency of series-connected multijunction solar cells. The theoretical method, based on the detailed balance model, is then applied to devices with 2 to 6 junctions under different illumination conditions. As results, (i) we show that the peaks in the efficiency distribution occur for recurrent values of bottom junction bandgap energy corresponding to atmospheric absorption in the solar spectrum, and (ii) we demonstrate that variations in the number of junctions, in the incident solar spectrum, and in the concentration factor lead to changes in the optimum bandgap energy set but that the bottom junction bandgap energy only changes among the recurrent values presented before. Additionally, we highlight that high conversion efficiencies take place for a broad distribution of bandgap energy combination, which make the choice of materials for the device more flexible. Therefore, based on the overall results, we propose more than a hundred III-V, II-VI and IV semiconductor material candidates to compose the bottom junction of highly efficient devices.

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Resumo A Lua traz muita curiosidade para os habitantes da Terra. Diversos mitos e crendices associados ao movimento do astro figuram no imaginário popular, conferindo-lhe um papel que beira o místico e o sobrenatural. Contudo, muitos desses mitos, ou concepções alternativas, são errôneos e persistentes, mas poderiam ser questionados com a simples observação sistemática do nosso único satélite natural. Neste trabalho, o resultado de um projeto que visa auxiliar a elucidação de um dos mitos envolvendo a Lua é apresentado. Mais especificamente, busca-se responder à pergunta de como se comparam suas fases quando observadas de diferentes pontos do globo terrestre. Já que uma imagem vale mais que mil palavras, a questão é abordada através de registros fotográficos de observações da Lua feitas de diferentes latitudes e longitudes do planeta através do projeto Fotos da Lua pelo Mundo. O resultado é conforme o esperado: a fase da Lua é a mesma para qualquer observador, mas o formato percebido muda dependendo da latitude. Ciente de que a abordagem da astrofotografia é muito difícil de ser aplicada na prática em uma sala de aula, propõe-se o uso do programa de computador Stellarium a fim de gerar as imagens que embasam as discussões deste trabalho.