The engineering of semiconductor materials for the development of solar cells is of great importance today. Two topics are considered to be of critical importance for the efficiency of Grätzel-type solar cells, the efficiency of charge separation and the efficiency of charge carrier transfer. Thus, one research focus is the combination of semiconductor materials with the aim of reducing charge recombination, which occurs by spatial charge separation. From an experimental point of view, the combining of materials can be achieved by decorating a core with a shell of another material resulting in a core-shell system, which allows control of the desired photoelectronic properties. In this context, a computational simulation is mandatory for the atomistic understanding of possible semiconductor combinations and for the prediction of their properties. Considering the construction of ZnO/ZnX (X = S, Se or Te) interfaces, we seek to investigate the electronic influence of the shell (ZnX) on the core (ZnO) and, consequently, find out which of the interfaces would present the appropriate properties for (Grätzel-type) solar cell applications. To perform this study, we have employed density functional theory (DFT) calculations, considering the Perdew-Burke-Ernzerhof (PBE) functional. However, it is well-known that plain DFT fails to describe strong electronic correlated materials where, in general, an underestimation of the band gap is obtained. Thus, to obtain the correct description of the electronic properties, a Hubbard correction was employed, i.e. PBE+U calculations. The PBE+U methodology provided the correct electronic structure properties for bulk ZnO in good agreement with experimental values (99.4%). The ZnO/ZnX interfaces were built and were composed of six ZnO layers and two ZnX layers, which represents the decoration process. The core-shell band gap was 2.2 eV for ZnO/ZnS, ∼1.71 eV for ZnO/ZnSe and ∼0.95 eV for ZnO/ZnTe, which also exhibited a type-II band alignment. Bader charge analysis showed an accumulation of charges in the 6th layer of ZnO for the three ZnO/ZnX interfaces. On the basis of these results, we have proposed that ZnO/ZnS and ZnO/ZnSe core-shell structures can be applied as good candidates (with better efficiency) for photovoltaic devices.

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Light scattering at rough interfaces is a standard approach to enhance absorption of light in the absorber layers of solar cells due to light trapping. In this work, an automata optimization algorithm, based on the Constructal Theory, is proposed for the heuristic geometric design to enhance light trapping of silicon solar cell surface textures. Surface textures were investigated computationally for light absorption of a normally incident simulated solar spectrum, under constraints of transverse area of the texture. The photogenerated current density was calculated for textures to estimate light trapping. In the automata optimization, Elemental Constructals, consisting of dielectric material blocks, were assembled on top of the solar cell forming a texture. Three variations of the proposed automata algorithm were tested and their capabilities were determined. The best result for this optimization was a photocurrent J=17.48mA/cm2 for grid periodicity above the wavelength and J=18.31mA/cm2 for grid periodicity in the sub-wavelength range. The evolutionary algorithm was also applied to assemble a periodic-disordered texture from fixed shape gratings to better harness incident light. Different textures with fixed shapes of gratings had been investigated to determine optimal geometric parameters. Optimized triangular, trapezoidal, and rounded-tip textures achieved the best results in this phase and were implemented to assemble the periodic-disordered texture which reached J=19.75mA/cm2 for triangular gratings. Results found with this pristine evolutionary algorithm corroborate its efficiency in finding, practically, geometries that lead to greater light absorption with a minimum amount of dielectric materials.

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