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Investigation of single phase Cu2ZnSnxSb1-xS4 compounds processed by mechanochemical synthesis

Publication . Neves, Filipe; Stark, A.; Schell, N.; Mendes, Manuel Joao; Aguas, H.; Fortunato, Elvira; Martins, Rodrigo; Correia, J.B.; Joyce, A

ABSTRACT: The copper zinc tin sulfide (CZTS) compound is a promising candidate as an alternative absorber material for thin-film solar cells. In this study, we investigate the direct formation of Cu1.92ZnSnx(Sb1-x)S-4 compounds [CZT(A)S], with x = 1, 0.85, 0.70, and 0.50, via a mechanochemical synthesis (MCS) approach, starting from powders of the corresponding metals, zinc sulfide, and sulfur. The thermal stability of the CZT(A)S compounds was evaluated in detail by in situ synchrotron high-energy x-ray diffraction measurements up to 700 degrees C. The CZT(A)S compounds prepared via MCS revealed a sphalerite-type crystal structure with strong structural stability over the studied temperature range. The contribution of the MCS to the formation of such a structure at room temperature is analyzed in detail. Additionally, this study provides insights into the MCS of CZTS-based compounds: the possibility of a large-scale substitution of Sn by Sb and the production of single phase CZT(A)S with a Cupoor/Zn-poor composition. A slight increase in the band gap from 1.45 to 1.49-1.51 eV was observed with the incorporation of Sb, indicating that these novel compounds can be further explored for thin-film solar cells.

2018Journal article

Open access

Ultrafast low-temperature crystallization of solar cell graded formamidinium-cesium mixed-cation lead mixed-halide perovskites using a reproducible microwave-based process

Publication . Brites, Maria João; Barreiros, M. Alexandra; Corregidor, V.; Alves, L. C.; Pinto, Joana V.; Mendes, Manuel Joao; Fortunato, Elvira; Martins, Rodrigo; Mascarenhas, João

ABSTRACT: The control of morphology and crystallinity of solution-processed perovskite thin-films for solar cells is the key for further enhancement of the devices’ power conversion efficiency and stability. Improving crystallinity and increasing grain size of perovskite films is a proven way to boost the devices’ performance and operational robustness, nevertheless this has only been achieved with high-temperature processes. Here, we present an unprecedented low-temperature (<80 °C) and ultrafast microwave (MW) annealing process to yield uniform, compact, and crystalline FA0.83Cs0.17Pb(I(1–x)Brx)3 perovskite films with full coverage and micrometer-scale grains. We demonstrate that the nominal composition FA0.83Cs0.17PbI1.8Br1.2 perovskite films annealed at 100 W MW power present the same band gap, similar morphology, and crystallinity of conventionally annealed films, with the advantage of being produced at a lower temperature (below 80 °C vs 185 °C) and during a very short period of time (∼2.5 min versus 60 min). These results open new avenues to fabricate band gap tunable perovskite films at low temperatures, which is of utmost importance for Mechanically flexible perovskite cells and monolithic perovskite based tandem cells applications.

2019Journal article

Open access

Prediction of sunlight-driven CO2 conversion: producing methane from photovoltaics, and full system design for single-house application

Publication . Vieira, F.; Sarmento, B.; Machado, Ana; Facão, Jorge; Carvalho, Maria João; Mendes, Manuel Joao; Fortunato, Elvira; Martins, Rodrigo

ABSTRACT: CO2 capture and utilization (CCU) technologies are being immensely researched as means to close the anthropogenic carbon cycle. One approach known as artificial photosynthesis uses solar energy from photovoltaics (PV), carbon dioxide and water to generate hydrocarbon fuels, being methane (CH4) a preferential target due to the already in place infrastructures for its storage, distribution and consumption. Here, a model is developed to simulate a direct (1-step) solar methane production approach, which is studied in two scenarios: first, we compare it against a more conventional 2-step methane production route, and second, we apply it to address the energetic needs of concept buildings with usual space and domestic hot water heating requirements. The analysed 2-step process consists in the PV-powered synthesis of an intermediate fuel - syngas - followed by its conversion to CH4 via a Fischer -Tropsch (methanation) process. It was found that the 1-step route could be adequate to a domestic, small scale use, potentially providing energy for a single-family house, whilst the 2-step can be used in both small and large scale applications, from domestic to industrial uses. In terms of overall solar-to-CH4 energy efficiency, the 2-step method reaches 13.26% against the 9.18% reached by the 1-step method. Next, the application of the direct solar methane technology is analysed for domestic buildings, in different European locations, equipped with a combination of solar thermal collectors (STCs) and PV panels, in which the heating needs that cannot be fulfilled by the STCs are satisfied by the combustion of methane synthesized by the PV-powered electrolyzers. Various combinations of situations for a whole year were studied and it was found that this auxiliary system can produce, per m(2) of PV area, in the worst case scenario 23.6 g/day (0.328 kWh/day) of methane in Stockholm, and in the best case scenario 47.4 g/day (0.658 kWh/day) in Lisbon.

2019Journal article

Open access

Ultrafast low-temperature crystallization of solar cell graded formamidinium-cesium mixed-cation lead mixed-halide perovskites using a reproducible microwave-based process [Poster]

Publication . Brites, Maria João; Barreiros, M. Alexandra; Corregidor, V.; Alves, L. C.; Pinto, Joana V.; Mendes, Manuel Joao; Fortunato, Elvira; Martins, Rodrigo; Mascarenhas, João

2019Conference object

Open access