At the end of 2017 roughly 1.8% of the worldwide electricity came from solar photovoltaics (PV), which is foreseen to have a key role in all major future energy scenarios with an installed capacity around 5 TW by 2050. Despite silicon solar cells currently rule the PV market, the extremely more versatile thin film-based devices (mainly Cu(In,Ga)Se 2 and CdTe ones) have almost matched them in performance and present room for improvement. The low availability of some elements in the present commercially available PV technologies and the recent strong fall of silicon module price below 1 $/W p focused the attention of the scientific community on cheap earth-abundant materials. In this framework, thin film solar cells based on Cu 2 ZnSnS 4 (CZTS) and the related sulfur selenium alloy Cu 2 ZnSn(S,Se) 4 (CZTSSe) were strongly investigated in the last 10 years. More recently, chalcogenide PV absorbers potentially able to face TW range applications better than CZTS and CZTSSe due to the higher abundance of their constituting elements are getting considerable attention. They are based on both MY 2 (where M = Fe, Cu, Sn and Y = S and/or Se) and Cu 2 XSnY 4 (where X = Fe, Mn, Ni, Ba, Co, Cd and Y = S and/or Se) chalcogenides. In this work, an extensive review of emerging earth-abundant thin film solar cells based on both MY 2 and Cu 2 XSnY 4 species is given, along with some considerations on the abundance and annual production of their constituting elements.

This paper reports the electrical characterization of commercially available crystalline silicon solar cells encapsulated with poly-vinylacetate doped with different Eu 3R organic complexes. The inclusion of these complexes in the encapsulating matrix allows down-shifting of the solar spectrum components below 420 nm toward the maximum quantum efficiency of the solar cells. This effect has been proven under Air Mass 1Á5 conditions (simulating terrestrial applications) where an increase of the total power delivered by the encapsulated cells has been observed. Moreover, this enhancement has been obtained using very low percentage by weight of organolanthanide dopants, allowing a reduction in the Watt peak price. At higher concentrations a strong quenching of the energy transfer from the organic antenna to the lanthanide ion has been observed.

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Photoluminescence (PL) and deep level transient spectroscopy (DLTS) measurements were used to study the origin of optical emissions in the 0.8–1.0 eV region of selected oxygen precipitated and dislocated silicon samples. It was shown that the D1 band, present in both types of samples, is the convolution of different sub-bands, narrowly spaced between 0.802 and 0.820 eV. The emission at 0.807 eV, assigned in the literature to dislocations, was found only in samples where dislocations were intentionally generated by plastic deformation or induced by the clustering of self-interstitials generated during the growth of oxide precipitates. A comparison of the results of PL, DLTS, and optical DLTS measurements allows the assignment of levels involved in the radiative recombination processes.

In this work we present a study of a p-type Czochralski-grown Si ingot which was grown using 10% solar grade silicon ͑SoG-Si͒. As the SoG-Si contains a relatively high concentration of impurities including phosphorus, the electrical properties of the as-grown wafers from this ingot are affected by both the compensating dopants and other impurities. Measurements of the minority charge carrier lifetime in the as-grown material reveal very low values ͑4-8 s͒. The Hall mobilities at room temperature correspond to normal values for Czochralski silicon in the upper part of the ingot ͑which solidifies first͒ and decrease significantly toward the bottom of the ingot. Segregation leads to an accumulation of impurities toward the lower parts of the ingot as well as to a stronger increase in phosphorus than of boron, the latter of which results in a high compensation level ͑i.e., an increasing resistivity͒. A priori, both effects could be responsible for the degradation of the electrical properties in the lower parts of the ingot, whereas theoretical considerations show that the level of compensation should not cause a strong decrease in Hall mobility at room temperature. Untextured solar cells have been processed from wafers originating from different positions of the ingot. As expected, the phosphorus diffusion leads to a gettering effect: the recombination active impurities are removed out of the wafer volume. This results in relatively high efficiencies ͑Ͼ16% ͒ of the solar cells but does not show a strong correlation between ingot height and cell efficiency. This observation is also confirmed by the high bulk lifetimes ͑Ͼ200 s͒ measured after the process even for samples originating from the last solidified ͑lower͒part of the ingot. The Hall mobility of samples cut from finished solar cells has been measured and shows the same trend as the as-grown samples, the values for the bottom of the ingot still being very low. With the concentrations of boron and phosphorus studied up to this point, compensation showed no detrimental effect on the cell efficiency of industrial-like solar cells.

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Low iron, pale blue natural and synthetic sapphire samples were studied by low temperature absorption and luminescence spectroscopy. For comparison, a bicolour pink and blue corundum from Vietnam was also considered. From radioluminescence and photoluminescence excitation spectra of both Cr 3+ and Ti 3+ , experimental evidence was obtained for attributing an absorption band at 17 500 cm −1 , currently interpreted as Fe 2+ → Ti 4+ intervalence charge transfer, to overlapping crystal field transitions of Cr 3+ and Ti 3+ . An important role was also proposed for Cr 2+ ; indeed, it is possible to propose that the colour of pale blue sapphires is mainly determined by chromium in its two valence states while Ti 3+ and Fe 3+ have a minor role.

Dedicated to Professor Horst P. Strunk on the occasion of his 65th birthday 71.55.Cn, 72.20.Jv, 72.40.+w, 72.80.Cw, 84.60.Jt Photovoltaics is a promising but challenging opportunity for the environmentally clean production of electric energy, as the cost of the produced energy is still too high to compete with conventional thermal and nuclear sources, in spite of the scientific and technological progress occurred in this field after the first oil crisis of 1973. Among the problems which should be solved to make photovoltaics fully competitive, a breakthrough concerning the cost reduction of the base material is compulsory. Aim of this paper is to discuss the scientific and technological problems encountered in the development of solar silicon for its use in high efficiency and low cost solar cells, and to give some firm experimental evidences about its potentialities. OriginalPaper Cadmium Telluride; 0,42% CIS; 0,18% Amorphous Si; 8,30% a-Si on Cz Slice; 4,63% Si Film; 0,26% Ribbon Si; 3,50% Single cystal Si; 35,17% Polycrystal Si; 47,54%c) of a kind of a low-grade silicon, called solar grade silicon, which could be adapted to solar cell fabrication, without loosing conversion efficiency.The processes under a) were aimed at the production of crystalline, non-single crystal ingots, wafers and sheet and were developed under the hypothesis that casting processes are intrinsically lower in cost that the Czochralski one. The potential development of die molding processes for ribbon silicon growth looked even more advantageous. The penalty to be paid in this case is associated to the presence of grain boundaries and other structural defects in the material and to unavoidable contaminations due to the casting crucible and die materials.The processes under b) were and are based on the development of low cost variants of the Siemens C route, which, as it is well known, is based on the energy intensive, high temperature reduction of purified chlorosilanes to polycrystalline silicon. Recent studies carried under the auspices of the European Commission within the fifth Framework Program showed that this route hardly could succeed in getting a polycrystalline feedstock at less than 25 €/kg, against the actual price of 90 $/kg of that produced following the original Siemens route.Very complex looked [1] and still looks the solution of problems associated to the production of a low grade silicon using variants of the metallurgical (MG) silicon process, with the aim to find alternative routes for the production of a low cost, low energy intensive polycrystalline feedstock. It was, in fact, figured that any material based on this processes would contain a quite large amount of impurities and structural defects. Therefore, intense basic research studies were spent worldwide, with the objective of investigating the role of impurities and crystal defects on the minority carrier lifetime and minority and majority carriers mobility and to discover/develop remedies in their presence.It is well known that the work carried out in the...