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Abstract Kesterite Cu2ZnSnS4 (CZTS) solar cells are regarded as a promising photovoltaic technology owing to the non-toxic and earth-abundant constitutes. With the application of scalable and low-cost solution methods, the possibility of its commercialization can be further increased. This work explores preparing prominent CZTS films by an economically feasible successive ionic adsorption and reaction (SILAR) synthesis method. The obtained precursor with the Mo/ZnS/Cu2SnS3 structure requires appropriate substantial annealing under a chalcogen atmosphere to form kesterite CZTS films. The annealing process is therefore optimized to improve the film quality and the performance of solar cells. Specifically, the optimal annealing condition is determined by adjusting the annealing temperature and holding time, respectively. The CZTS film annealed at 580 °C for 60 min demonstrates better film quality in terms of surface morphology, crystallinity, and phase purity. Consequently, CZTS solar cells fabricated with the optimal absorber exhibit a preferable efficiency of up to 4.26%.

Abstract The power conversion efficiency of the photoelectrochemical cell AuRhodamine BAu was found to be (2.4 ± 0.2) × 10 −6 per cent under typical operating conditions. A ten-fold improvement could be expected from constructional modifications, but further increases in efficiency would require changes in the cell chemistry. The low power conversion efficiency can be related to a low (4.7 × 10 −2 per cent) efficiency for the production of the open circuit photovoltage; a low (2.2 × 10 −2 per cent) quantum efficiency for the production of the short circuit current; and to markedly non-rectangular voltage-current characteristics. The deviations from a rectangular relationship and the low efficiency of current production arise from mass-transport limitations rather than from ohmic losses or activation polarisation. The low voltage efficiency probably arises from inefficiencies in the photochemical and electron transfer steps which lead to photovoltage production. The limitations of this type of cell as a solar energy conversion device are discussed.

Abstract Organic photovoltaic (OPV) solar cells recently achieved a reported efficiency as high as 17.3%. In this study we explore new avenues of shifting the light absorber through rational design of the π-spacers in the Donor–π-spacer–Acceptor dyes. That is, to construct high performing new dyes with fixed donor (DCPA) and acceptor (PMID) from appropriate π-building units of fluorene, EDOT and thiophene. These three π-units form various combinations of the π-conjugate spacers for new dyes. We focus on the development of the relationship between the three building units of π-spacers to construct new DCPA–π-spacer–PMID dyes and their UV–vis spectra in tetrahydrofuran (THF) solution. The latter (i.e., UV–vis spectra) are calculated using quantum mechanical time dependent density functional theory (TD-DFT) methods. This set of nine new organic dyes has been employed to develop augmented intelligence (AI). We discovered that repeating the fluorene (πO) unit alone in the π-spacer, such as OP100, OP200 and OP300 dyes, will lead to hyperchromic enhancement of the donor spectral band in the UV region of ca. 300 nm, with limited impact on the major spectral band at 500 nm which is stemmed from the acceptor (PMID). To maximize the UV–vis absorption, more efficient π-spacers for this class of dyes are constructed from mixtures of the fluorene (πO) and EDOT (πP) units, such as πO-πP-πO (OP210) or as πO-πP-πO-πP (OP220). The information obtained is useful to elucidate new dyes with desired properties with appropriate UV–vis spectra for future machine learning (ML).

Abstract Whole sky spectral radiance distribution measurements are difficult and expensive to obtain, yet important for real-time applications of radiative transfer, building performance, physically based rendering, and photovoltaic panel alignment. This work presents a validated machine learning approach to predicting spectral radiance distributions (350–1780 nm) across the entire hemispherical sky, using regression models trained on high dynamic range (HDR) imagery and spectroradiometer measurements. First, we present and evaluate measured, engineered, and computed machine learning features used to train regression models. Next, we perform experiments comparing regular and HDR imagery, sky sample color models, and spectral resolution. Finally, we present a tool that reconstructs a spectral radiance distribution for every single point of a hemispherical clear sky image given only a photograph of the sky and its capture timestamp. We recommend this tool for building performance and spectral rendering pipelines. The spectral radiance of 81 sample points per test sky is estimated to within 7.5% RMSD overall at 1 nm resolution. Spectral radiance distributions are validated against libRadtran and spectroradiometer measurements. Our entire sky dataset and processing software is open source and freely available on our project website.

Abstract The construction of conventinal solar air collectors and the fact that they will operate with a significant pressure difference between the heated air stream and ambient, suggests that significant quantities of air may leak into or out of them. A search of the literature reveals no consideration of the effects these air leaks may have on the validity of collector efficiency measurements, on the efficiency itself, or indeed what the meaning of efficiency is under such operating conditions. This paper discusses the meaning of collector efficiency when leaks into the collector occur, analyses the effects on efficiency measurements, and solves the collector efficiency for the simple case of a constant leakage rate along the collector. Assuming that air leaking in from ambient can replace deliberate fresh air supply to the load as in building heating, then significant measurement errors are made if air leaks in to the collector are not accounted for. Further, the collector efficiency is increased over the no leak case, so that complex construction methods to make the collector air tight are probably not warranted.

Few-layer graphene films were grown by chemical vapor deposition and transferred onto n-type crystalline silicon wafers to fabricate graphene/n-silicon Schottky barrier solar cells. In order to increase the power conversion efficiency of such cells the graphene films were doped with nitric acid vapor and an antireflection treatment was implemented to reduce the sunlight reflection on the top of the device. The doping process increased the work function of the graphene film and had a beneficial effect on its conductivity. The deposition of a double antireflection coating led to an external quantum efficiency up to 90% across the visible and near infrared region, the highest ever reported for this type of devices. The combined effect of graphene doping and antireflection treatment allowed to reach a power conversion efficiency of 8.5% exceeding the pristine (undoped and uncoated) device performance by a factor of 4. The optical properties of the antireflection coating were found to be not affected by the exposure to nitric acid vapor and to remain stable over time.

A facile low-temperature synthetic method of growing semiconductor mesoporous single-crystal of anatase TiO2 directly on FTO substrate was developed. The templated hydrothermal synthesis approach was employed to make mesoporous single-crystal TiO2 that contains pores tens to hundreds of nanometres in size under low temperature, which opens a potential way to produce useful functional thin film photoanodes by one-pot approach for fabricating cheap and highly efficient optoelectronic devices. This method is based on seeded nucleation and growth inside a pre-formed mesoporous silica film template immersed in diluted precursor solution. The electrochemical characterizations showed that the directly grown mesoporous single-crystal thin film on FTO substrate has substantially higher conductivity and electron mobility than conventionally deposited TiO2 thin films by printing techniques. Hence, using the as-synthesized mesoporous single-crystal thin film baking at 150 degrees C as photoanodes, an encouraging 5.83% solar to electricity conversion efficiency was achieved. It is expected that the developed mesoporous single-crystals on FTO substrate may find broader applications in many different technologies. This generic synthetic strategy extends the possibility of mesoporous single-crystal films directly growing to a range of substrates. Moreover, this approach could work at lower temperatures below 150 degrees C, which could considerably minimize the environmental impact and production costs of high performance mesoporous materials. (C) 2015 Elsevier Ltd. All rights reserved.

Abstract The carrier lifetime is the most important electronic property of semiconductor materials for solar cells. In this paper we discuss traditional and novel methods for its experimental determination. Among the latter, the Quasi-steady-state photoconductance is particularly powerful since it permits measuring the injection level dependence of the lifetime. The analysis and interpretation of this dependence yields a wealth of information on the physical mechanisms that limit the performance of silicon solar cells. The effect of the surfaces of the silicon wafers, the emitter saturation current density and the Shockley–Read–Hall and Auger recombination mechanisms are explained and their possible determination from lifetime measurements discussed.