Photovoltaic (PV) devices have been used in space applications since 1958 and need to be constantly optimized in terms of specific power (W/kg). For the next decade, Mars is one important pursued destination by NASA and, as such, optimized PV designs will be needed. This work presents optimal designs in terms of bandgap energy configuration for multijunction solar cells operating at the Mars’ orbit conditions. For this, a physical model using blackbody radiation was implemented to calculate the solar spectrum at different orbital points and the PV solar cell temperature. By means of a computer simulation based on the Schockley-Queisser detailed balance model, power conversion efficiencies are mapped and the optimal bandgap energy combination is obtained for each configuration. As results, we obtained for the optimized double junction solar cell an efficiency of 45.3% with bandgaps of 0.90/1.60 eV and 51.7% for the best triple junction solar cell with bandgaps of 0.75/1.22/1.84 eV.

In this work we employ the transfer matrix method for the analysis of optical materials properties to simulate and optimize monolithic tandem solar cell devices based on CuIn 1− x Ga x Se 2 , CI(G)S, and perovskite (PVK) absorbers. By finding models that fit well the experimental data of the CI(G)S solar cell, the semitransparent perovskite solar cell (PSC) and the PVK/CI(G)S monolithic tandem solar cell, we were able to perform a detailed optical loss analysis that allowed us to determine sources of parasitic absorption. We found better substitute materials for the transport layers to increase the power conversion efficiency and, in case of semitransparent PSCs, sub-bandgap transmittance. Our results set guidelines for the monolithic PVK/CI(G)S tandem solar cells development, predicting an achievable efficiency of 30%.

In this work, we investigate the influence of structure parameters of strain compensated InGaAs/ InGaP multiple quantum wells on the optical and mechanical properties of the system. With theoretical simulations, we show that this system is suitable to operate within the entire 1.05-1.50 eV range without surpassing the critical layer thicknesses. Therefore, we propose its use as the active region of intermediate junctions in multijunction solar cells for specific applications. Furthermore, we present experimental results demonstrating the tunability of the transition energy of this system from 1.28 to 1.40 eV. In order to reach the bottommost part of this range (1.35-1.28 eV) though, GaAs interlayers between the barriers and the quantum wells are required. We show that the introduction of interlayers serves both to tailor the strain between the layers and block the interdiffusion of As/P at the heterointerface.

In this review article solar cells based on III-V materials are addressed, starting by a brief description of their operation principle, including key materials’ issues. Subsequently, the different types of III-V solar cells are presented, together with their state-of-the-art performance. Various approaches to reduce their costs are then discussed, and an outlook of the research in this field concludes the paper.

We present a study on the role and optimization of diffraction gratings used as back reflector/scatterer in multiresonant GaAs ultrathin solar cells. We show the influence of parameters variation for the grating and for the pattern on the diffraction efficiencies. With an optimized square pattern, we show a record-high absorption of 92.5% in a 100 nm-thick GaAs absorber. Accounting for parasitic absorption, the estimated short-circuit current is 26.4 mA/cm2. We also discuss routes towards even higher currents by breaking the degeneracy of the modes with non-symmetric structures.

Electrically active defects present in three InAs/GaAs quantum dots (QDs) intermediate band solar cells grown by metalorganic vapor phase epitaxy have been investigated. The devices’ structures are almost identical, differing only in the growth temperature and thickness of the GaAs layers that cover each InAs QD layer. These differences induce significant changes in the solar energy conversion efficiency of the photovoltaic cells, as previously reported. In this work, a systematic investigation was carried out using deep level transient spectroscopy (DLTS) and Laplace DLTS measurements on control samples and solar cell devices, which have clearly shown that electrically active traps play an important role in the device figures of merit, such as open circuit voltage, short circuit current, and shunt resistance. In particular, it was found that the well-known EL2 defect negatively affects both the open circuit voltage and shunt resistance, more in structures containing QDs, as a consequence of the temperature cycle required to deposit them. Other unidentified defects, that are absent in samples in which the QDs were annealed at 700 °C, contribute to a reduction of the short circuit current, as they increase the Shockley-Read-Hall recombination. Photoluminescence results further support the DLTS-based assignments.

In this work, we propose a self-consistent interactive model based on the detailed balance approach to investigate the impact of luminescence coupling (LC) in multijunction solar cells (MJSCs). The proposed model is innovative in not using any empiric parameter input in considering the interactive nature of LC within the detailed balance framework to correlate the emissive and electrical properties of the junctions under interaction. We apply the model to radiative-limited series-connected MJSCs under different illumination conditions to demonstrate the influence of LC on the current matching condition and the impact on the power conversion efficiency (PCE) limits of such devices. As a result, we show that LC does not change the optimum bandgap energy combination leading to the highest PCE for a given operation condition but widens the span of configurations reaching high PCE, information that aids in the design of high PCE MJSC. Additionally, we analyzed some selected MJSC configurations with two to six junctions, well known from the literature to reach high PCE under different illumination conditions showing that even better performance can be achieved without either the need for changing the existent active materials or using optical thinning but using more efficient photon management concepts. Finally, we indicate MJSC configurations that can achieve high PCE for terrestrial applications under high coupling conditions, including some promises for low-cost high-efficiency photovoltaics, especially the ones involving stacks with silicon, perovskites, chalcogenides, and/or III–V materials.

Astrophotography has been responsible for the discovery of planets, solar systems, stars, and several other celestial objects, which directly helps with expanding our knowledge about the universe and creating scientific models for nature. Practical techniques have been extensively described, including Covington, who has published an extensive guide to amateur astrophotography. Furthermore, aiming to introduce such important scientific activity among students, several authors have described possibilities of using the technique in physics and astronomy teaching. However, the proposed activities and methods normally need expensive equipment, such as telescopes, professional cameras, mounts, tripods, optical components, and other items not commonly owned by teachers, students, or the general public.The ubiquity of the smartphone, especially among students, makes it interesting for educational purposes. The device can be used as a mobile laboratory due to the several integrated sensors. Furthermore, the possible uses in classroom are extensive, including the ones involving astronomical subjects, especially with the use of its camera for sky imaging. In this work, we propose a simple and low-cost technique for the practice of astrophotography using the smartphone. Moreover, we suggest teaching activities involving the STEAM disciplines (science, technology, engineering, the arts, and math), including the analysis of the Earth’s rotation and the artistic treatment of the astrophotographs.

In the past few decades, the use of low dimensional structures has evolved from a basic science laboratory to a solution for both the improvement of existing electronic and optoelectronic devices and the development of new ones. In the particular case of devices based on nanostructured III–V semiconductor materials such as lasers, LEDs, and photodetectors, their improved performance has been extensively demonstrated and they are already on the market. This is not fully the case for solar cells yet. It is true that research on solar cells has started many decades ago, but in this century, mostly due to the predicted consequences of global warming and the energetic challenge the world is facing, the field received an extra push and the investigation of potential improvement in solar energy conversion efficiency using nanostructures was only natural to be pursued. In this chapter, we discuss the use of III–V semiconductor quantum wells, quantum wires, and quantum dots as alternatives to boost the performance of solar cells.

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.

The multijunction solar cell concept has proven to be a very efficient way of converting solar into electrical energy. Theoretical calculations using the detailed balance model aim in the optimization process of finding the best materials (in terms of bandgap energies) to compose the device junctions. However, along with other simplifications, such model applied to multijunction solar cells fails in considering one important physical effect: the luminescence coupling amongst the junctions. In this work, we present a method based on a self-consistent numerical approach for implementing the luminescence coupling in the detailed balance model applied to multijunction solar cells. We show results on the influence of the effect on the performance of different dual junction solar cells in which a coupling factor and the junction bandgap energies are varied. Therefore, we show that the main impact of the luminescence coupling is in the raise of the solar cell short circuit current, and consequently, their conversion efficiencies. Moreover, we highlight that the influence of the effect is more important for the bandgap energy combinations that would lead to low efficiencies. This is an important result towards the choice of materials by allowing more combinations to achieve high efficiencies.

Electrical current mismatching is a well-known limitation of triple junction solar cells that lowers the final conversion efficiency. Several solutions have been proposed to face this issue, including the insertion of a multiple quantum well structure as the intermediate junction’s active material. With a better matching in the current among the junctions, the total current increases, thus modifying the working conditions of the overall device. In this way, the InGaP top junction needs to be optimized to such new condition. In this work, numerical simulations were carried out aiming the enlargement of the electrical current density of an InGaP pn junction to achieve the proper current matching in triple junction solar cell for spatial applications. The optimized structure has been grown in a GaAs substrate and characterized as a single junction solar cell. Although the measured short circuit current density and conversion efficiency are still well below the theoretically predicted values, processing improvement should lead to adequate cell performance.

Theoretical simulations of solar cell current-voltage characteristics provide important information for a better design of the device structure, such as layers thicknesses and doping levels, in order to obtain high photovoltaic conversion efficiency. The inclusion of precise material parameters is critical to obtain reliable results and detailed understanding of the simulated device operation. In this study, GaAs solar cell structures were simulated by drift-diffusion model with SCAPS-1D in order to optimize the performance under 1 sun illumination. Moreover, we used the published results of some devices as references to infer their structures, as the details are normally not completely disclosed by the authors. To do so, an optimization study was required to probe different materials, thicknesses and doping levels for the layers. With the inferred structure, it was possible to evaluate the possibility of improvements through variation of the structure parameters to achieve even higher efficiencies.

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.

Altas resistências elétricas em série e baixas resistências em paralelo são fontes de perdas em dispositivos fotovoltaicos. Em dispositivos que operam sob concentração, esses costumam ser os principais fatores limitantes para o aumento da eficiência de conversão. Excluindo fatores externos associados a falhas no processo de produção, a resistência elétrica em série depende de fatores intrínsecos aos materiais e à estrutura de camadas do dispositivo fotovoltaico. Dessa forma, para minimizar o seu valor é extremamente importante planejar adequadamente esses parâmetros construtivos antes da produção dos dispositivos. Um dos fatores mais impactantes na resistência em série é o desenho da malha de dedos coletores do contato elétrico frontal. Por outro lado, minimizar a resistência em série do contato elétrico requer o aumento da área metálica da superfície frontal, que serve de janela para a radiação solar. Portanto, deve haver um compromisso na redução das perdas elétricas e ópticas. Nesse trabalho, apresentamos os resultados da otimização do desenho da malha de dedos coletores para o contato elétrico frontal para três diferentes geometrias obtidas por algoritmos genéticos. As geometrias escolhidas foram a retangular, tradicional para a produção desse tipo de dispositivo, a hexagonal e a diamante. Além disso, comparamos os resultados obtidos com os de um dispositivo produzido com uma malha otimizada por um método de cálculo analítico. Ao final, discutimos as melhorias introduzidas pelas novas geometrias e apresentamos a configuração otimizada, que foi obtida com a geometria hexagonal que reduziu as perdas em 47,71%.

A Resolução 02/2015 do Conselho Pleno do Conselho Nacional de Educação estabeleceu novas Diretrizes Curriculares Nacionais (DCN) para os cursos de formação inicial e continuada de professores, onde se incluem os cursos de licenciatura. Nesse trabalho, apresentamos uma proposta curricular para um curso de licenciatura em física na modalidade presencial (noturna) em adequação com as novas DCN. Apesar da imposição da reestruturação de todos os cursos a nível nacional em até dois anos, não foi esse o principal motivador de nossa revisão curricular, haja visto que o processo já havia sido iniciado com a instauração de uma Comissão de Reformulação no ano anterior à publicação da resolução. Dessa forma, apresentamos, nesse trabalho, as mudanças realizadas para cumprimento das exigências legais, bem como a discussão do processo reflexivo e autocrítico vivido na elaboração desse currículo, o qual se baseia na experiência acumulada pelos autores desse trabalho, professores, alunos e funcionários, ao longo dos oito anos de oferta do Curso de Licenciatura em Física do CEFET/RJ campus Petrópolis. Além das análises reflexivas, descrevemos também às análises quantitativas de evasão e retenção ao longo da oferta do curso que justificaram as mudanças propostas.

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.

Células solares de múltiplas junções são uma alternativa às tradicionais células simples para aumento da eficiência de conversão de energia por dispositivos fotovoltaicos. Em função de seu elevado custo, elas são utilizadas em aplicações onde o custo não é um limitante primordial. Neste trabalho, apresentamos a situação atual do desenvolvimento de células solares de junção tripla para aplicações espaciais no Laboratório de Semicondutores da PUC-Rio. Nos estudos relacionados a esse projeto, trabalhamos na otimização das três junções individualmente. O material ativo escolhido para a junção inferior é o germânio, que possui um gap de energia de cerca de 0,7 eV. A junção é produzida por difusão de dopantes tipo n em substrato tipo p. Assim, forma-se a primeira junção. Em seguida, realizamos os estudos da heteroepitaxia de semicondutores do tipo III-V sobre o Ge que é o substrato da estrutura, pois tanto a junção intermediária como a do topo são baseadas em semicondutores III-V. Para a junção intermediária propomos utilizar um conjunto de poços quânticos de InGaAs com barreira de InGaP. Essa estratégia permite o controle do gap de energia efetivo que aparece nessa região por conta do confinamento dos portadores de carga elétrica. A vantagem de utilizar essa abordagem é que não há um material bulk com parâmetro de rede compatível e que apresente o valor ótimo de gap de energia, conforme o calculado teoricamente (1,18 eV). Além disso, é esperado que os materiais utilizados no sistema de poços quânticos apresentem maior resistência à radiação cósmica que os materiais comumente utilizados. Finalmente, o material ativo da junção superior é o InGaP, com um gap de energia de 1,8 eV. A otimização dessa junção passa pelo aumento de sua corrente de curto-circuito, que pode ser um fator limitante para o dispositivo como um todo.