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In the last decade, lead triiodide perovskite (APbI3) (A: organic cation) solar cells (PSCs) have been broadly studied due to their promising features related to the low cost, easy manufacturing process, and stability. Strategies to improve the device stability include the application of techniques such as compositional engineering of the cation of these halide perovskites, but it is still a complex task to find the right balance between the stability and power conversion efficiency of materials and complete devices. In this work, we performed a combined study of five samples of [5-AVA(1−x)MAx]PbI3 (5-AVA: ammonium valeric acid and MA: methylammonium) with x = 1.0, 0.75, 0.5, 0.25 and 0.0, using X-ray diffraction (XRD) and UV-VIS spectroscopy measurements in combination with periodic density functional theory (DFT) based calculations. Our samples showed an optical bandgap of 1.58 eV and the coexistence of the two phases as observed by XRD analyses. The theoretical results of the bandgaps for the no mixed phases (x = 1.0 and x = 0.0) show good agreement with the experiment, obtaining bandgap values overestimated by 0.18 eV and 0.33 eV, respectively. A direct relation between the number of 5-AVA ions in the samples and the stability of the phases was theoretically found and proved through the increment observed in the bandgap and the cohesive energy. We proposed a compositional strategy for perovskites [5-AVA(1−x)MAx]PbI3 with x values of at most 0.5, based on the small blue-shift and the low absorbance reduction of the spectrum curve, added to the small phase stabilization found. [ABSTRACT FROM AUTHOR]

Microstructural properties of Cu2ZnSn(SxSe1−x)4 kesterite solid solutions were investigated using grazing incidence X-ray diffraction for the full interval of anion compositions in order to explore the influence of S and Se atoms on the thin film morphology. Thin films were prepared by sputtering deposition of metallic precursors, which were then submitted to a high temperature sulfo-selenization process. By adjusting process parameters samples from sulfur- to selenium-pure (0 ≤x≤ 1) were made. Microstructural analysis shows a strong dependence of domain size and microstrain on composition. Both values increase with higher sulfur content, and depth profile analysis by grazing incidence X-ray diffraction shows selenium-rich films tend to have a more homogeneous depth distribution of domain size. The increasing trend in domain size of S-rich absorbers can be related to lower formation energies of the sulfur binary phases leading to formation of kesterites, while the increase in the microstrain is explained by the substitution of larger Se atoms with smaller S atoms in the host lattice and the presence of secondary phases. [ABSTRACT FROM AUTHOR]

In this work we report on the effect of alkali doping via Na and/or K introduction into flexible and light-weight Cu2ZnSnSe4 (CZTSe) solar cells obtained using a sequential process based on the sputtering of metallic stacks and further reactive annealing. Different thicknesses of Cr diffusion barriers and 50 μm thick ferritic steel substrates were used. We compare different doping methods: Na-doped Mo targets (MoNa), SLG underneath the flexible substrates, NaF and KF pre-absorber synthesis evaporation (PAS) and post-deposition evaporation (PDT). Additionally, we report on the importance of the Cr barrier and back contact modification to improve solar cell performance. A remarkable enhancement in the absorber grain size and surface morphology occurred especially when using Na via MoNa and PAS. Nevertheless, preliminary experiments led to better results for MoNa doping due to a higher Na content confirmed by TOF-SIMS. K doping via PAS also showed promising results. An increase in the efficiency of solar cells from 2.2% to 4.3% was possible when using a MoNa layer sandwiched between regular Mo layers. The improvement is mainly related to a higher VOC and FF. After performing a detailed Cr and back contact optimization, a record value of 6.1% for flexible CZTSe solar cells was recently obtained using MoNa and a new surface Ge doping. [ABSTRACT FROM AUTHOR]

Microstructural properties of Cu2ZnSn(S(x)Se(1-x))4 kesterite solid solutions were investigated using grazing incidence X-ray diffraction for the full interval of anion compositions in order to explore the influence of S and Se atoms on the thin film morphology. Thin films were prepared by sputtering deposition of metallic precursors, which were then submitted to a high temperature sulfo-selenization process. By adjusting process parameters samples from sulfur- to selenium-pure (0 ≤ x ≤ 1) were made. Microstructural analysis shows a strong dependence of domain size and microstrain on composition. Both values increase with higher sulfur content, and depth profile analysis by grazing incidence X-ray diffraction shows selenium-rich films tend to have a more homogeneous depth distribution of domain size. The increasing trend in domain size of S-rich absorbers can be related to lower formation energies of the sulfur binary phases leading to formation of kesterites, while the increase in the microstrain is explained by the substitution of larger Se atoms with smaller S atoms in the host lattice and the presence of secondary phases.