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The efficiency record of industrial type PERC solar cells exceeded 22% at the turn of the year 2015 to 2016. Our best screen-printed PERC solar cell reached 22.04% efficiency while the best cell batch showed a very narrow efficiency distribution. A detailed electrical and optical loss analysis of those industrial type high efficiency PERC solar cells is carried out which enables further optimization and strategic improvements. A variety of characterization data allows for a recombination current density, resistance and optical loss analysis based on numerical device simulation, analytical calculations and raytracing, respectively. The main recombination losses at maximum power point (MPP) occur in the homogenous and selective diffused regions of the emitter. A series resistance loss analysis is analytically performed. The emitter contribution to the lumped series resistance dominates the series resistance losses. The optical loss analysis performed with raytracing shows main reflection and absorption losses in the rear metal layer which is partly due to the light trapping capability of the PERC cells.

openaire: EC/FP7/307315/EU//SOLARX Light and elevated-temperature induced degradation (LeTID) is currently a severe issue in passivated emitter and rear cells (PERC). In this work, we study the impact of surface texture, especially a black silicon (b-Si) nanostructure, on LeTID in industrial p-type mc-Si PERC. Our results show that during standard LeTID conditions the b-Si cells with atomic-layer-deposited aluminum oxide (AlOx) front surface passivation show no degradation despite the presence of a hydrogen-rich AlOx/SiNx passivation stack on the rear. Furthermore, b-Si solar cells passivated with silicon nitride (SiNx) on the front lose only 1.5 %rel of their initial power conversion efficiency, while the acidic-textured equivalents degrade by nearly 4 %rel under the same conditions. Correspondingly, clear degradation is visible in the IQE of the acidic-textured cells, especially in the ~850–1100 nm wavelength range confirming that the degradation occurs in the bulk, while the IQE remains nearly unaffected in the b-Si cells. The observations are supported by spatially-resolved photoluminescence (PL) maps, which show a clear contrast in the degradation behavior of b-Si and acidic-textured cells, especially in the case of SiNx front surface passivation. The PL maps also suggest that the magnitude of LeTID scales with surface area of the texture, rather than wafer thickness that was recently reported, although the b-Si cells are slightly thinner (140 vs. 165 µm). The results indicate that b-Si has a positive impact on LeTID, and hence, benefits provided by b-Si are not limited only to the excellent optical properties, as commonly understood.

In this work we compare experimental results of an industrial passivated emitter and rear cell (PERC) high volume pilot line production in the SolarWorld Innovations technology center with a simulation model based on 2D Sentaurus Device Simulations The PERC solar cell design shows in a well-controlled experiment a 1.1% absolute higher median efficiency compared to the aluminium back surface field (Al-BSF) solar cell reference group. We derive a calibrated simulation model by the characterization of cells and test structures. We show that the simulation model reproduces well the measured I-V data. In consequence this enables us to estimate the solar cell performance when an applied process or silicon wafer parameters will be changed for further optimization. In the second part of this study we investigate the impact of front and rear side recombination on the solar cell parameters by simulation and sensitivity analysis. We show that the quality of the local BSF underneath the local rear contacts has an important impact on the electrical solar cell performance.

The reaction of metallic silver with tungsten tetrachlorideoxide WOCl4 or the reaction of AgCl with WOCl3, both at 690 K, lead to Ag1–x[W2O2Cl6] as black lustrous crystal needles. The compound shows a substantial phase field width in the silver content depending on reaction temperature and reaction time and crystals with x = 0, 0.38 and 0.82 were isolated. The crystal structure determinations (monoclinic, C2/m) show the structure to be isotypic to those of Tl[W2O2Cl6] and K0.84[W2O2Cl6] with the presence of 1D polymeric [W2O2Cl6]n strands and Ag+ ions with a variety in the occupation of the respective crystallographic site. Ag1–x[W2O2Cl6] represents a mixed valence compound with a variable ratio of W(IV) and W(V) in the W2 dumbbells with a short W–W separation of 2.85 A. In Fourier maps the electron density of the Ag ion appears smeared over a large area. By structure determinations of stoichiometric Ag1.0[W2O2Cl6] at temperatures of 123, 193, and 293 K a double minimum potential was found with the silver ion dynamically disordered over two flat basins with a thermal activation barrier of 13 meV. No long range ion mobility is present since the Ag+ ions are trapped within a coordinating cage consisting of ten chlorine atoms of the surrounding [W2O2Cl6] strands forming a distorted bicapped cube. By MAS-NMR spectroscopic measurements on the 109Ag nuclei at different temperatures, the spin lattice relaxation times were determined giving a thermally activated barrier of 15 meV. The electronic conductivity of pressed powder samples of Ag[W2O2Cl6] by a four-probe measurement applying direct current is 1 Ω–1·cm–1 at room temperature and 10–3 Ω–1·cm–1 at 25 K. For the conduction mechanism at low temperatures a variable range hopping mechanism is suggested, whereas at higher temperatures a standard semi-conductivity with a bandgap of 60 meV is present.

The reaction of CuCl with WOCl3 at 400 °C leads to a mixture of Cu1−x[W2O2Cl6] (1) and Cu1−x[W4O4Cl10] (2) in form of black lustrous needles. Both compounds crystallize in space group C2/m with a = 12.7832(5) A, b = 3.7656(2) A, c = 10.7362(3) A, β = 119.169(2)° for 1 and a = 12.8367(19) A, b = 3.7715(7) A, c = 15.955(3) A, β = 102.736(5)° for 2. The structures are made up of WO2Cl4 octahedra. In the case of 1 two octahedra are edge-sharing via chlorine atoms to form pairs which are linked via the trans-positioned oxygen atoms to form infinite double strands . In the structure of 2 two of these double strands are condensed via terminal chlorine atoms to form quadruple strands . Like for all members of the Mx[W2O2X6] structure family (X = Cl, Br) nonstochiometry with respect to the cations M was observed. The copper content of 1 and 2 was derived from the site occupation factors of the respective structure refinements. For several crystals examined the copper content varied between x = 0.27 and 0.17 for 1 and x = 0.04 for 2. In both structures the oxochlorotungstate strands are negatively charged and connected to layers by the monovalent copper ions, which are tetrahedrally coordinated by the non-bridging chlorine atoms of the strands. The structure models imply disorder of the Cu+ ions over closely neighboured sites.

The reaction of alkali chlorides MCl with NbOCl3 yields melts which on cooling solidify under crystallization. In the case of KCl / NbOCl3, the pink coloured regulus was investigated by powder-XRD and shown to be biphasic, consisting of K[NbOCl4] (primitive orthorhombic lattice, a = 13.467(2); b = 7.9362(8); c = 14.041(2) A) and K2[NbOCl5] (F centred cubic lattice, a = 9.8291(2) A). To a small amount vapour phase transport occurs and colourless crystals of M2[Nb3O5Cl7] (M = K, Rb, Cs) are deposited in the colder parts of evacuated glass tubes containing molten mixtures of MCl and NbOCl3 or MCl, Nb2O5 and NbCl5 in a temperature gradient of 500 °C to 450 °C for some days. Green crystals of (NH4)2[Nb3O5Br7] are obtained as a by-product in the reaction of NH4Br with NbOBr3 in sealed ampoules at temperatures of 300 °C. All compounds are isotypic and belong to the M2[Nb3O5X7] structure type of which (NH4)2[Nb3O5Cl7] was already known (Schweda, 1997) (monoclinic, C2/c, Z = 4, (NH4)2[Nb3O5Br7] a = 17.8488(6), b = 8.8581(3), c = 11.3376(4) A, β = 110.572(2)°; K2[Nb3O5Cl7] a = 16.7346(3), b = 8.8558(2), c = 11.0623(3) A, β = 112.661(1)°; Rb2[Nb3O5Cl7] a = 16.794(14), b = 8.873(5), c = 11.032(8) A, β = 111.33(6)°; Cs2[Nb3O5Cl7] a = 17.233(6), b = 8.928(3), c = 11.092(3), β = 109.36(2)°). The structures consist of niobium-centred NbO3Cl3 and NbO4Cl2 octahedra, which share common edges to form a two-dimensional network of the composition (X = Cl, Br). These anionic layers are stacked with the cations located between them. The monovalent cations are coordinated exclusively by halogen atoms and have the coordination number ten in form of “edshammar polyhedra”.

The crystal structure of WOCl3, determined on the basis of powder diffraction data (tetragonal, P42/mnm, a = 10.6856 ( 6 ) , c = 3.8537 ( 2 ) ), is isotypic to WOI3 and contains one-dimensional strands of edge-sharing double-octahedral W2O4/2Cl6 groups connected via common corners in trans position. A W–W bond of 2.99 A is present within the planar W2Cl6 groups. A series of non-stochiometric, mixed valence W(IV,V) compounds M1−x[W2O2Cl6] can be obtained from WOCl3 by reaction with metal halides (TlCl, KCl, PbCl2) or by reaction of elemental Hg with WOCl4. All were characterized by single crystal structure determinations and EDX measurements (Tl0.981(2)[W2O2Cl6]: monoclinic, C2/m, a = 12.7050 ( 4 ) , b = 3.7797 ( 1 ) , c = 10.5651 ( 3 ) A , β = 107.656 ( 1 ) ° ; K0.84(2)[W2O2Cl6]: monoclinic, C2/m, a = 12.812 ( 3 ) , b = 3.7779 ( 6 ) , c = 10.196 ( 3 ) A , β = 107.422 ( 8 ) ° ; Pb0.549(3)[W2O2Cl6]: orthorhombic, Immm, a = 3.7659 ( 1 ) , b = 9.8975 ( 4 ) , c = 12.1332 ( 6 ) A ; Hg0.554(6)[W2O2Cl6]: monoclinic, C2/m, a = 12.8361 ( 8 ) , b = 3.7622 ( 3 ) , c = 10.2581 ( 9 ) A , β = 113.645 ( 3 ) ° ). Two representatives of this family of compounds have already been reported: Na[W2O2Br6] [Y.-Q. Zhang, K. Peters, H.G. von Schnering, Z. Anorg. Allg. Chem. 624 (1998) 1415–1418] and Ag0.74[W2O2Br6] [S. Imhaine, C. Perrin, M. Sergent, Mat. Res. Bull. 33 (1998) 927–933]. The Ag containing compound can be obtained from elemental Ag and WOBr3. The crystal structure, originally reported in the triclinic system, was redetermined and shown to be monoclinic with space group C2/m ( a = 13.7338 ( 10 ) , b = 3.7769 ( 3 ) , c = 10.7954 ( 9 ) A , β = 112.401 ( 3 ) ° ). The crystal structures of these compounds are in close relationship to the structure of WOCl3 and all contain W2O4/2X6 (X=Cl, Br) double strands with the mono and divalent cations coordinated by the terminal halogen atoms of the W2X6 groups and a short W–W bond (2.85 A for X=Cl). A cube-shaped coordination environment is present for M=Tl, K and a trigonal-prismatic coordination for M=Ag, Hg. Hg0.55[W2O2Cl6] is a semiconductor with a non-Arrhenius behaviour, high specific conductivity of 0.05 Ω–1 cm−1 and a very small activation energy of 0.03 eV. Hg0.55[W2O2Cl6] and Ag0.8[W2O2Br6] show a temperature independent paramagnetism with a magnetic moment around 300×10–6 cm3 mol–1.

Black, needle shaped crystals of NbOBr2 were formed by reduction of NbOBr3 with InBr at 500 °C. It crystallizes isotypically to NbOI2 (monoclinic, space group C2, a = 13.833(4), b = 3.9079(6), c = 7.023(2) A, β = 105.026(10)°). The structure consists of NbO2Br4 octahedra, which are connected to layers . Nb atoms of edge sharing octahedra form Nb2 pairs with Nb–Nb distances of 3.144(5) A. Within corner-sharing octahedra alternating long and short Nb–O bonds are present, causing the polarity of the structure.