Abstract. We use the very deep and homogeneous I-band selected dataset of the FORS Deep Field (FDF) to trace the evolution of the luminosity function over the redshift range 0.5 < z < 5.0. We show that the FDF I-band selection down to I AB = 26.8 misses of the order of 10% of the galaxies that would be detected in a K-band selected survey with magnitude limit K AB = 26.3 (like FIRES). Photometric redshifts for 5558 galaxies are estimated based on the photometry in 9 filters (U, B, Gunn g, R, I, SDSS z, J, K and a special filter centered at 834 nm). A comparison with 362 spectroscopic redshifts shows that the achieved accuracy of the photometric redshifts is ∆z/(z spec + 1) ≤ 0.03 with only ∼1% outliers. This allows us to derive luminosity functions with a reliability similar to spectroscopic surveys. In addition, the luminosity functions can be traced to objects of lower luminosity which generally are not accessible to spectroscopy. We investigate the evolution of the luminosity functions evaluated in the restframe UV (1500 Å and 2800 Å), u , B, and g bands. Comparison with results from the literature shows the reliability of the derived luminosity functions. Out to redshifts of z ∼ 2.5 the data are consistent with a slope of the luminosity function approximately constant with redshift, at a value of −1.07 ± 0.04 in the UV (1500 Å, 2800 Å) as well as u , and −1.25 ± 0.03 in the blue (g , B). We do not see evidence for a very steep slope (α ≤ −1.6) in the UV at z ∼ 3.0 and z ∼ 4.0 favoured by other authors. There may be a tendency for the faint-end slope to become shallower with increasing redshift but the effect is marginal. We find a brightening of M * and a decrease of φ * with redshift for all analyzed wavelengths. The effect is systematic and much stronger than what can be expected to be caused by cosmic variance seen in the FDF. The evolution of M * and φ * from z = 0 to z = 5 is well described by the simple approximations Mfor M * and φ * . The evolution is very pronounced at shorter wavelengths (a = −2.19, and b = −1.76 for 1500 Å rest wavelength) and decreases systematically with increasing wavelength, but is also clearly visible at the longest wavelength investigated here (a = −1.08, and b = −1.29 for g ). Finally we show a comparison with semi-analytical galaxy formation models.Key words. galaxies: luminosity function, mass function -galaxy: fundamental parameters -galaxies: high-redshiftgalaxies: distances and redshifts -galaxies: evolution

25.5% efficiency is demonstrated for monolithic perovskite/silicon tandem solar cell using textured foil and the impact of texture position on performance and energy yield is simulated.

Abstract. We present a catalogue and atlas of low-resolution spectra of a well defined sample of 341 objects in the FORS Deep Field. All spectra were obtained with the FORS instruments at the ESO VLT with essentially the same spectroscopic set-up. The observed extragalactic objects cover the redshift range 0.1 to 5.0. 98 objects are starburst galaxies and QSOs at z > 2. Using this data set we investigated the evolution of the characteristic spectral properties of bright starburst galaxies and their mutual relations as a function of redshift. Significant evolutionary effects were found for redshifts 2 < z < 4. Most conspicuous are the increase of the average C IV absorption strength, of the dust reddening, and of the intrinsic UV luminosity, and the decrease of the average Lyα emission strength with decreasing redshift. In part the observed evolutionary effects can be attributed to an increase of the metallicity of the galaxies with cosmic age. Moreover, the increase of the total star-formation rates and the stronger obscuration of the starburst cores by dusty gas clouds suggest the occurrence of more massive starbursts at later cosmic epochs.

Singlet exciton fission is an exciton multiplication process that occurs in certain organic materials, converting the energy of single highly-energetic photons into pairs of triplet excitons. This could be used to boost the conversion efficiency of crystalline silicon solar cells by creating photocurrent from energy that is usually lost to thermalisation. An appealing method of implementing singlet fission with crystalline silicon is to incorporate singlet fission media directly into a crystalline silicon device. To this end, we developed a solar cell that pairs the electron-selective contact of a high-efficiency silicon heterojunction cell with an organic singlet fission material, tetracene, and a PEDOT:PSS hole extraction layer. Tetracene and n-type crystalline silicon meet in a direct organic-inorganic heterojunction. In this concept the tetracene layer selectively absorbs blue-green light, generating triplet pairs that can dissociate or resonantly transfer at the organo-silicon interface, while lower-energy light is transmitted to the silicon absorber. UV photoemission measurements of the organicinorganic interface showed an energy level alignment conducive to selective hole extraction from silicon by the organic layer. This was borne out by current-voltage measurements of devices subsequently produced. In these devices, the silicon substrate remained well-passivated beneath the tetracene thin film. Light absorption in the tetracene layer created a net reduction in current for the solar cell, but optical modelling of the external quantum efficiency spectrum suggested a small photocurrent contribution from the layer. This is a promising first result for the direct heterojunction approach to singlet fission on crystalline silicon.

We examine rest-frame ultraviolet spectra of 70 high-redshift quasars (z ! 3:5) to study the chemical enrichment history of the gas closely related to the quasars and thereby estimate the epoch of first star formation. The fluxes of several ultraviolet emission lines were investigated within the framework of the most recent photoionization models to estimate the metallicity of the gas associated with the high-redshift quasars. Standard photoionization parameters and the assumption of secondary nitrogen enrichment indicate an average abundance of Z=Z ' 4-5 in the line-emitting gas. Assuming a timescale of evol ' 0:5 0:8 Gyr for the chemical enrichment of the gas, the first major star formation for quasars with z ' 4 should have started at a redshift of z f ' 6 8, corresponding to an age of the universe of several times 10 8 yr (H 0 ¼ 65 km s À1 Mpc À1 , M ¼ 0:3, Ã ¼ 0:7). We note that this also appears to be the era of reionization of the universe. Finally, there is some evidence for a positive luminosity-metallicity relation in this high-redshift quasar sample.

We present the B-band Tully-Fisher relation (TFR) of 60 late-type galaxies with redshifts 0.1 − 1. The galaxies were selected from the FORS Deep Field with a limiting magnitude of R = 23. Spatially resolved rotation curves were derived from spectra obtained with FORS2 at the VLT. High-mass galaxies with v max 150 km/s show little evolution, whereas the least massive systems in our sample are brighter by ∼ 1 − 2 mag compared to their local counterparts. For the entire distant sample, the TFR slope is flatter than for local field galaxies (−5.77 ± 0.45 versus −7.92 ± 0.18). Thus, we find evidence for evolution of the slope of the TFR with redshift on the 3 σ level. This is still true when we subdivide the sample into three redshift bins. We speculate that the flatter tilt of our sample is caused by the evolution of luminosities and an additional population of blue galaxies at z 0.2. The mass dependence of the TFR evolution also leads to variations for different galaxy types in magnitude-limited samples, suggesting that selection effects can account for the discrepant results of previous TFR studies on the luminosity evolution of late-type galaxies.

We numerically maximize the achievable photocurrent density of planar perovskite-silicon tandem solar cells for different device architectures. For the optimizations we combine the transfer-matrix method with a simulated annealing algorithm. The optimizations are conducted within experimentally accessible and relevant layer-thickness ranges, which allows to extract applicable device guidelines. A comparison between regular and inverted tandem-cell designs reveals that a rear-emitter silicon heterojunction in combination with an inverted perovskite top-cell can yield a photocurrent, which is 1.4 mA/cm higher than that of tandem cells with the usual polarity and a front-emitter silicon bottom cell. Switching from the regular to the inverse architecture leads to over 2% (absolute) gain in power conversion efficiency. Finally we show that an efficiency of 30.8% is achievable for such tandem cells with an optimized perovskite band-gap.

Perovskite–silicon tandem solar cells offer the possibility of overcoming the power conversion efficiency limit of conventional silicon solar cells. Various textured tandem devices have been presented aiming at improved optical performance, but optimizing film growth on surface-textured wafers remains challenging. Here we present perovskite–silicon tandem solar cells with periodic nanotextures that offer various advantages without compromising the material quality of solution-processed perovskite layers. We show a reduction in reflection losses in comparison to planar tandems, with the new devices being less sensitive to deviations from optimum layer thicknesses. The nanotextures also enable a greatly increased fabrication yield from 50% to 95%. Moreover, the open-circuit voltage is improved by 15 mV due to the enhanced optoelectronic properties of the perovskite top cell. Our optically advanced rear reflector with a dielectric buffer layer results in reduced parasitic absorption at near-infrared wavelengths. As a result, we demonstrate a certified power conversion efficiency of 29.80%.