Solar-grade multicrystalline silicon ingots as raw material for solar cells were obtained from upgraded metallurgical silicon by directional solidification in an axial magnetic field. The influence of preparation technology on the microstructural characteristics of silicon ingots was investigated. Governing equations were used to simulate the silicon fluid flow and thermal fields during directional solidification. The results show that appropriately increasing melt temperature and/or decreasing pulling-down rate can be conductive to the growth of a coarse columnar grain. Meanwhile, the axial magnetic field promotes the formation of low-energy ∑3 twin boundaries and reduces the dislocations and impurities, where the total concentration of major metal impurities is with a mean of 0.459 ppmw in the range of 1/9 to 8/9 of height along the growth direction. It is shown from the simulation results that suppressing silicon melt flow in both radial and azimuthal directions and reducing the growth rate in the edge regions contribute to the formation of a flat solid–liquid interface, which is more consistent with the experimental results. Moreover, the formation mechanism of the twins and removal mechanism of the impurities were discussed.

Surface sulfurization of Cu(In,Ga)Se2 (CIGSe) absorbers is a commonly applied technique to improve the conversion efficiency of the corresponding solar cells, via increasing the bandgap towards the heterojunction. However, the resulting device performance is understood to be highly dependent on the thermodynamic stability of the chalcogenide structure at the upper region of the absorber. The present investigation provides a high-resolution chemical analysis, using energy dispersive X-ray spectrometry and laser-pulsed atom probe tomography, to determine the sulfur incorporation and chemical re-distribution in the absorber material. The post-sulfurization treatment was performed by exposing the CIGSe surface to elemental sulfur vapor for 20 min at 500°C. Two distinct sulfur-rich phases were found at the surface of the absorber exhibiting a layered structure showing In-rich and Ga-rich zones, respectively. Furthermore, sulfur atoms were found to segregate at the absorber grain boundaries showing concentrations up to ~7 at% with traces of diffusion outwards into the grain interior.

In situ and operando measurement techniques combined with nanoscale resolution have proven invaluable in multiple fields of study. We argue that evaluating device performance as well as material behavior by correlative X-ray microscopy with <100 nm resolution can radically change the approach for optimizing absorbers, interfaces and full devices in solar cell research. In this article, we thoroughly discuss the measurement technique of X-ray beam induced current and point out fundamental differences between measurements of wafer-based silicon and thin-film solar cells. Based on reports of the last years, we showcase the potential that X-ray microscopy measurements have in combination with in situ and operando approaches throughout the solar cell lifecycle: from the growth of individual layers to the performance under operating conditions and degradation mechanisms. Enabled by new developments in synchrotron beamlines, the combination of high spatial resolution with high brilliance and a safe working distance allows for the insertion of measurement equipment that can pave the way for a new class of experiments. Applied to photovoltaics research, we highlight today’s opportunities and challenges in the field of nanoscale X-ray microscopy, and give an outlook on future developments.

The research and development of novel photovoltaic technologies is going through a golden era, thanks to the demonstration of remarkable efficiencies across a broad range of semiconductor classes and device architectures. In parallel with these developments, the opportunities for characterizing the structure of a semiconductor film in situ of a processing step have also increased, to the extent that in situ and in operando experiments are becoming readily accessible to researchers. These combined advances represent the subject matter of this article, wherein studies that improve our understanding of structure formation and evolution in perovskite and organic semiconductor films for innovative solar cells are reviewed. Although focus is placed on the dynamics of semiconductor film formation, the review also highlights recent research on environmental testing, a key component in the development of materials with high intrinsic stability.

The demands for highly transparent thin films for many integrated optical systems increase rapidly. The aim of the present work is to address these important needs. We show a novel approach for the nanocolloidal processing of barium titanate with enhanced optical transparency. The results showed that the stability of the prepared solution and optical transparency of the resulted thin film improved significantly. The study of the structure and properties of the prepared solutions indicated that the enhanced and homogenous transparency is due to the size-effect of the particles embedded in the solution, which are nanostructured. It seems to us that the proposed method has the capability of being a general strategy for obtaining highly transparent solutions and thin films. Moreover, the enhanced transparency of the prepared thin films can improve the energy efficiency of the solar power systems significantly.

An analysis of the nucleation mechanism of pyramids formed in (100) silicon in Na2CO3/NaHCO3 solution has been carried out. This texturization process of silicon by means of Na2CO3/NaHCO3 solutions is of special interest because it can be applied to the silicon solar cell industry to texture solar cell surfaces to decrease the front reflection and enhance light trapping in the cells. For this purpose, two microscopy techniques—scanning electron microscopy and atomic force microscopy—have been used to study the different stages of pyramidal nucleation and formation. The different aspects and factors involved in the texturization process require different analysis conditions and microscopy resolution. Tracing the transformation of determined surface areas and structures has been achieved, contributing clarification of the mechanism of pyramid nucleation in Na2CO3/NaHCO3 solutions.

The present work shows results on elemental distribution analyses in Cu(In,Ga)Se2 thin films for solar cells performed by use of wavelength-dispersive and energy-dispersive X-ray spectrometry (EDX) in a scanning electron microscope, EDX in a transmission electron microscope, X-ray photoelectron, angle-dependent soft X-ray emission, secondary ion-mass (SIMS), time-of-flight SIMS, sputtered neutral mass, glow-discharge optical emission and glow-discharge mass, Auger electron, and Rutherford backscattering spectrometry, by use of scanning Auger electron microscopy, Raman depth profiling, and Raman mapping, as well as by use of elastic recoil detection analysis, grazing-incidence X-ray and electron backscatter diffraction, and grazing-incidence X-ray fluorescence analysis. The Cu(In,Ga)Se2 thin films used for the present comparison were produced during the same identical deposition run and exhibit thicknesses of about 2 μm. The analysis techniques were compared with respect to their spatial and depth resolutions, measuring speeds, availabilities, and detection limits.

La puissance débitée par les systèmes solaires ne cesse d’augmenter, soit par l’amélioration du rendement de conversion, soit par la multiplication des techniques de fabrication des photopiles solaires. Devant l’offre de fortes sources d’énergies conventionnelles à des prix relativement bas, l’utilisation du silicium polycristallin aboutit aux cellules polycristallines à faible coût de production. Cependant, les paramètres photovoltaïques de ce type de cellules sont affectés par l’existence des joints de grains et la ségrégation des impuretés à leurs niveaux. Ceci nous a ammené à nous intéresser dans le cadre de ce travail à l’influence des traitements thermiques sur le comportement électrique des couches de silicium polycristallin destinées à des applications photovoltaïques. Les résultats obtenus ont montré que les couches dopées arsenic sont plus résistives que celles dopées bore, et que les traitements thermiques réduisent le nombre de porteurs piégés et la quantité d’atomes de dopant aux joints de grains. D’autre part, cette étude nous a permis de constater que l’élévation de la température des traitements thermiques favorise l’augmentation de la conductivité électrique. De plus, la conductivité électrique dans des couches dopées bore est plus élevée que celle dans des couches dopées arsenic.

In this paper, a clear view on the bulk microstructure of MDMO-PPV:PCBM blends as used in bulk hetero-junction organic solar cells is obtained by means of TEM (Transmission Electron Microscopy). Using TEM, 3-dimensional information is acquired on phase separated regions, formed during casting. Particle statistics illustrate quantitatively that a.o. drying conditions and choice of solvent dramatically influence the blend structure. More information about the lateral blend structure and distribution is obtained in cross-sectional view. Since blend morphology is strongly related to photovoltaic performance, TEM can be a powerful tool for understanding today's photovoltaic performances and screening new sets of materials.