The latest progress and future perspectives of thin film photovoltaic kesterite technology are reviewed herein. Kesterite is currently the most promising emerging fully inorganic thin film photovoltaic technology based on critical raw‐material‐free and sustainable solutions. The positioning of kesterites in the frame of the emerging inorganic solar cells is first addressed, and the recent history of this family of materials briefly described. A review of the fast progress achieved earlier this decade is presented, toward the relative slowdown in the recent years partly explained by the large open‐circuit voltage (V_OC) deficit recurrently observed even in the best solar cell devices in the literature. Then, through a comparison with the close cousin Cu(In,Ga)Se₂ technology, doping and alloying strategies are proposed as critical for enhancing the conversion efficiency of kesterite. In the second section herein, intrinsic and extrinsic doping, as well as alloying strategies are reviewed, presenting the most relevant and recent results, and proposing possible pathways for future implementation. In the last section, a review on technological applications of kesterite is presented, going beyond conventional photovoltaic devices, and demonstrating their suitability as potential candidates in advanced tandem concepts, photocatalysis, thermoelectric, gas sensing, etc.

This work presents a complete analysis of all Raman active modes of Cu₂ZnSnS₄ measuring with six different excitation wavelengths from near infrared to ultraviolet. Simultaneous fitting of spectra allowed identification of 18 peaks from device grade layers with composition close to stoichiometry that are attributed to the 27 optical modes theoretically expected for this crystalline structure, including detection of 5 peaks not observed previously, but theoretically predicted. Resonance effects are assumed to explain the observed increase in intensity of weak modes for near infrared and ultraviolet excitations. These results are particularly relevant for experimental discrimination of Raman modes related to secondary phases.

Secondary phases like Cu₂SnS₃ are major obstacles for kesterite thin film solar cell applications. We prepare Cu₂SnS₃ using identical annealing conditions as used for the kesterite films. By x-ray diffraction, the crystal structure of Cu₂SnS₃ was identified as monoclinic. Polarization-dependent Raman investigations allowed the identification of the dominant peaks at 290 cm⁻¹ and 352 cm⁻¹ with the main A′ symmetry vibrational modes from the monoclinic Cu₂SnS₃ phase. Furthermore, micro-resolved Raman investigations revealed local variations in the spectra that are attributed to a secondary phase (possibly Cu₂Sn₃S₇). This exemplifies the abilities of micro-resolved Raman measurements in the detection of secondary phases.

The correlation between the structural (average size and density) and optoelectronic properties [band gap and photoluminescence (PL)] of Si nanocrystals embedded in ${\mathrm{SiO}}_2$ is among the essential factors in understanding their emission mechanism. This correlation has been difficult to establish in the past due to the lack of reliable methods for measuring the size distribution of nanocrystals from electron microscopy, mainly because of the insufficient contrast between Si and ${\mathrm{SiO}}_2.$ With this aim, we have recently developed a successful method for imaging Si nanocrystals in ${\mathrm{SiO}}_2$ matrices. This is done by using high-resolution electron microscopy in conjunction with conventional electron microscopy in dark field conditions. Then, by varying the time of annealing in a large time scale we have been able to track the nucleation, pure growth, and ripening stages of the nanocrystal population. The nucleation and pure growth stages are almost completed after a few minutes of annealing time at 1100 °C in ${\mathrm{N}}_2$ and afterward the ensemble undergoes an asymptotic ripening process. In contrast, the PL intensity steadily increases and reaches saturation after 3–4 h of annealing at 1100 °C. Forming gas postannealing considerably enhances the PL intensity but only for samples annealed previously in less time than that needed for PL saturation. The effects of forming gas are reversible and do not modify the spectral shape of the PL emission. The PL intensity shows at all times an inverse correlation with the amount of $P_b$ paramagnetic centers at the ${\mathrm{Si–SiO}}_2$ nanocrystal–matrix interfaces, which have been measured by electron spin resonance. Consequently, the $P_b$ centers or other centers associated with them are interfacial nonradiative channels for recombination and the emission yield largely depends on the interface passivation. We have correlated as well the average size of the nanocrystals with their optical band gap and PL emission energy. The band gap and emission energy shift to the blue as the nanocrystal size shrinks, in agreement with models based on quantum confinement. As a main result, we have found that the Stokes shift is independent of the average size of nanocrystals and has a constant value of 0.26±0.03 eV, which is almost twice the energy of the Si–O vibration. This finding suggests that among the possible channels for radiative recombination, the dominant one for Si nanocrystals embedded in ${\mathrm{SiO}}_2$ is a fundamental transition spatially located at the ${\mathrm{Si–SiO}}_2$ interface with the assistance of a local Si–O vibration.