Tin sulfide (SnS) semiconductor has recently attracted a great deal of attention from the scientific community regarding its application in solar cells. However, SnS solar cell efficiencies are still limited to less than 5%. The incorporation of nanostructures into solar cells has been demonstrated to be a potential route to improve device performance. So far, there have been no reports on the incorporation of nanostructures into SnS solar cells. In this work, a theoretical study on the incorporation of tin sulfide selenide (SnSSe) nanostructures in the form of quantum wells (QWs) into SnS solar cells under the radiative limit is presented, for the first time. In particular, the impact of well number, well thickness, and Se/(S + Se) compositional ratio at the wells, on solar cell characteristics, is evaluated. An efficiency enhancement of 11.1% is found for a SnS/SnSSe QW solar cell, compared to the optimized device without nanostructures, for 50 wells of 54 nm width with a Se/(S + Se) well composition of 0.4 and considering barrier thicknesses of 5 nm, which is a result of the increase in short-circuit current density of 14.5%. The influence of defects at wells and barriers, as well as defects at interfaces, on solar cell behavior is also presented, demonstrating that the introduction of QWs can result in higher efficiencies than that of the device without nanostructures. In this sense, the addition of SnSSe nanostructures to SnS solar cells is introduced as a potential route to promote the absorption of photons with energy lower than the SnS band-gap, while keeping open-circuit voltage values similar to those of a SnS solar cell without nanostructures, thereby increasing solar cell efficiency.

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Following the chronological stages of calculations imposed by the WIEN2K code, we have performed a series of density functional theory calculations, from which we were able to study the effect of strain on the kesterite structures for two quaternary semiconductor compounds Cu2ZnGeS4 and Cu2ZnGeSe4. Remarkable changes were found in the electronic and optical properties of these two materials during the application of biaxial strain. Indeed, the band gap energy of both materials decreases from the equilibrium state, and the applied strain is more pronounced. The main optical features are also related to the applied strain. Notably, we found that the energies of the peaks present in the dielectric function spectra are slightly shifted towards low energies with strain, leading to significant refraction and extinction index responses. The obtained results can be used to reinforce the candidature of Cu2ZnGeX4(X = S, Se) in the field of photovoltaic devices.

In this work, an analysis of the luminescent properties of zirconium oxide (ZrO2) doped with Er 3+ in three different concentrations was performed to investigate which sample could be useful for optoelectronic applications. To achieve it, a set of four samples of ZrO2:Er 3+ with the variation in Er 3+ concentration about 0%, 0.1%, 0.2% y 0.3% were synthesized by the sol-gel method. The luminescence measurements for all samples were performed using an excitation wavelength of 380 nm, by this way the upconversion spectrum for the sample containing the 0.2% of Er 3+ was measured at 980 nm. The luminescence spectra showed three emission bands attributed to the electronic transitions 4 F7/2→ 4 I15/2, 2 H11/2→ 4 I15/2, and 2 S3/2→ 4 I15/2, all this band belonged to Er 3+ radiative transitions, we found that the sample with 0.2% presented a higher emission intensity at 550 nm compared with the others samples, also the average lifetime was calculated, we found that this value decrease with the increment of Er 3+ concentration, finally, the upconversion spectrum were measured for the sample with higher luminescent intensity at 380 nm, the result revealed that the most probable emission after the photon absorption is that around 550 nm.

Gold plasmonic nanoparticles are receiving attention for a variety of types of NIR optical biomedical imaging including photoacoustic imaging. Herein we present a novel method to assemble equilibrium gold nanoclusters from 5 nm primary gold nanospheres, which exhibit high near-infrared (NIR) absorbance and subsequently fully dissociate back to primary particles, which has the potential to enable renal clearance. The nanoparticle assembly is manipulated via controlling colloidal interactions, specifically electrostatic repulsion and depletion attraction. The charge on the primary ~5 nm gold nanospheres is tailored via place exchange reactions with a variety of biocompatible ligands such as citrate, lysine and cysteine. The primary particles form clusters upon addition of a biodegradable polymer, PLA(1k)-b-PEG(10k)-b-PLA(1k), followed by controlled solvent evaporation. The cluster size may be tuned from 20-40 nm in diameter by manipulating the gold and polymer concentrations along with the solvent evaporation extent. Salt is also added to increase the NIR absorbance and reduce the nanocluster size by reducing polymer adsorption. The adsorption of the polymer onto the Au surfaces effectively quenches the nanoclusters. High NIR absorption facilitates photoacoustic imaging, even for the small cluster sizes. In response to acidic cellular pH environments, the polymer degrades and the clusters dissociate back to primary particle on the order of 5 nm, which are small enough for renal clearance.