Abstract

The use of controlled inert ambient to produce hybrid perovskite solar cells (PSCs) makes them less competitive towards the commercialization. Herein, progress is made with the preparation of hybrid perovskite (CH3NH3PbI3) in a high relative humidity (RH ~ 60%) ambient condition by using a mixture of ethyl acetate (EA) and 4-Tertbutyl-Pyridine (tBP) as anti-solvent. A small amount of tBP helps to form a more homogeneous perovskite surface with a higher hydrophobicity. The mixture of EA and tBP is found to be an efficient anti-solvent to extract the primary solvent and moisture in the precursor solution and form mirror-like perovskite thin films.

More than 200 perovskite solar cells, with active area of 0.1 cm2, were prepared with the perovskite thin films prepared under ambient conditions. It is showed that a small amount of tBP in EA improves consistently all the photovoltaic parameters of our PSCS, from an average efficiency of 8.64% over 113 cells with only EA as anti-solvent to 13.64% over 131 cells with EA + tBP as the anti-solvent. More than 55% of the last ones show efficiencies higher than 16%. The champion cell, recording an efficiency of 17.41% in the beginning and reaching the maximum efficiency of 18.04%, remains more than 80% of the initial efficiency after more than 180 days of storage in ambient conditions without encapsulation. The proposed method opens the possibility to fabricate highly efficient and stable perovskite solar cells under ambient condition without glove box.

Abstract

In this work, an experimental and theoretical study on CH3NH3PbI3 perovskite solar cells was performed. A theoretical validation of experimental results in perovskite solar cells with efficiencies of 13.32% is presented. An optimization study which involves the spiro-OMeTAD and perovskite thickness’ influence on electrical output parameters (Voc, Jsc, FF and PCE) showed a promotion of solar cell efficiency to 15.50% under 100 nm and 400 nm for hole transport material and absorber, respectively. The importance of the diffusion length of the absorber is discussed. In order to enhance the efficiency, a study of defect density (NT) was applied at the range of 1016 cm−3 (experimental) to 1010 cm−3 (theoretical) where we achieved an efficiency of 20.26%. The present work illustrates the importance of thickness optimization and the reduction of defect density (by the improvement of the quality of processed film) to obtain a better performance of this type of solar cell. Furthermore, the relevance of the implementation of a back contact with higher work function was studied.

Abstract

Interfacial charge transfer is a determining factor for the development of highly efficient solar cells. In antimony-based solar cells, interfacial engineering at the absorber/electron transport material interface relies on the use of a toxic CdS interlayer. In this work, an environmental-friendly interfacial engineering approach for planar Sb2S3 solar cells was implemented by using graphene-based nanoribbons. Graphene nanoribbons (GNR) and sulfur-doped graphene nanoribbons (S-GNR) sheets were incorporated as interlayer between TiO2 and Sb2S3 films in planar Sb2S3 solar cells, resulting in an enhanced photovoltaic performance up to 4.1%. Kelvin probe and C-V measurements revealed that the improvement was related to the superior built-in voltage due to the lower work function of the graphene-based interlayers along with a suitable cascade interfacial charge transfer. More importantly, surface photovoltage transient and intensity-modulated photocurrent and photovoltage spectroscopies also demonstrated that the presence of these interlayers decreased the electron transport time and suppressed the formation of interfacial states, which in turns reduced the interfacial recombination pathways boosting the performance of the devices fabricated. Although S-doped GNR provides the best results, more work is in progress to determine the cause of increased efficiency and the lack of significant Voc increase.

Abstract

Concentrating solar power (CSP) systems use solar absorbers to convert sunlight into thermal electric power. In CSP systems, a high reflective surface focuses sunlight onto a receiver that captures the solar energy and converts it into heat. The operation of high efficiency CSP systems involves improvements in the performance of the coatings of the solar absorption materials. To accomplish this, novel, more efficient selective coatings are being developed with high solar absorptance and low thermal losses at their operation temperature. Heat losses in a CSP system occur by three mechanisms: conduction, convection and radiation. It has been widely documented that energy losses increase with increasing operating temperature of CSP systems, and the precise knowledge of the thermophysical properties of the materials involved in CSP systems may allow us to increase the efficiency of systems.

In this work, we applied the pulsed photoradiometry technique (PPTR) to evaluate the changes in the thermophysical properties of selective coatings on a variety of substrates as a function of temperature. Three types of coatings deposited with two different techniques on three types of substrate were examined: commercial coatings based on titanium oxynitride deposited by sputtering on substrates of copper and aluminum, coatings based on black nickel deposited by electrochemical methods on substrates of steel, and coatings based on black cobalt deposited by electrochemical methods on substrates of steel and copper. Values of the thermal diffusivity and thermal conductivity were obtained in the temperature range of 25 to 550 °C. Optical reflectance measurements have been performed in order to provide an estimate of the dependence of the thermal emittance on temperature using the black body radiation theory. REFERENCES

Abstract

The numerical evaluation of the radiative heat transfer in a multichanneled solar reactor coated with ZnFe2O4 thin-film is performed by using a channel-level simulation. A ray-tracing simulation of a 25 kW solar furnace allows obtaining the radiation distribution at each channel aperture. Then a Monte Carlo ray tracing is performed to analyze the radiative heat transfer on the monolith to optimize the channel-level geometry and film thickness for maximum absorptance and more homogeneous temperature distributions. The model considers the optical properties of ZnFe2O4 films deposited on zirconia substrate, obtained through the characteristic matrix method. This approach allows accounting for important reactor design parameters and operational conditions, such as ZnFe2O4 layer thickness, incoming radiation profile, diameter and length of pores and position of the monolith in the focal zone of the solar furnace.

Abstract

The use of concentrated solar energy in processing ceramic materials is an attractive route to obtain these materials with low CO2 emissions. In this work, nanostructures of monoclinic zirconia (m-ZrO2) were obtained using concentrated solar energy provided by the IER-UNAM solar furnace as a heat source. In the first stage of the process, a Zr/O/C complex was obtained by sol-gel method at a temperature of 120 °C using zirconium n-propoxide and sorbitol as precursors reagents. This complex was used in a second stage to obtain m-ZrO2 by heating it at a temperature of 1200 °C for one hour in air atmosphere. This last stage was performed in a solar furnace. Samples were analyzed by characterization techniques: FT-IR, TGA/DSC, XRD, TEM, and SEM confirming the formation of nanostructures of zirconia in monoclinic phase.

Abstract

20 A methodology for the evaluation of the specularity error of a polymeric film optical coating is presented. The methodology is based on the comparison of images from the sun produced by two high quality spherical mirrors, one covered with a highly specular evaporated aluminum film, and the second one with the polymeric film under study. This film is a commercial product known as Reflectech®. To determine the specularity error, both images are reproduced by means of ray tracing optical simulations. Those simulations use the angular brightness distribution from the sun as input, which were recorded by means of a specially developed solar scope. Significant differences are obtained between images of the sun generated by both mirrors. However, the specularity error of the coating under consideration is found to be just 0.71 mrad. This error is quite small making the polymeric coating highly appropriate for point focus concentration systems. This is illustrated by calculations for a parabolic dish concentrator.

Abstract

The optical quality of concentrators has a direct impact on the thermal efficiency of concentrating solar power plants. There is a need to evaluate the quality of the mirrors before installation and during operation. A review of the optical characterization techniques that have been developed for solar concentrators is presented. A brief description of the operation and methodology of each technique is done. The strengths and possible vulnerabilities of the techniques are also discussed. A classification of the different techniques in families according to their underlying principles of operation is proposed. Finally an analysis of the available information about the accuracy and precision of the different methods is carried out.

Abstract

In the literature for photocatalytic reaction modeling engineering, several simplified schemes applicable to ambient temperature radiative transfer for scattering media are available. A popular strategy is the Six-Flux method because it is simple and is not computer time demanding but its accuracy is not always explicit. In the present work we assess the accuracy of low order methods, including six flux case, by solving the radiative transfer equation in dimensionless form within a cubic enclosure, for i) a collimated beam and ii) a diffuse beam. Radiation enters the cube through a square window centered on one face and with an area one quarter the area of the face. The simulation considers fully absorbing walls, and isotropic scattering. The deviations of simplified models based on Discrete Ordinate or Finite Volume schemes, are compared to the mesh independent solution. The results indicate that for a collimated beam boundary condition the Six-Flux model and more refined models are moderate. The error of the total rate of energy absorbed (TREA) and that of the local volumetric rate of energy absorption (LVREA) with respect to a mesh independent solution are below 5% and 22% respectively. In contrast, it is found that for diffuse boundary conditions the Six-Flux model is very inaccurate since the corresponding errors are larger than 120%.

Abstract

A multiscale model is presented to describe the radiation absorption field in photocatalytic reactors with supported catalyst. The characteristic matrix method is applied at the photocatalyst layer scale, and is embedded within a Monte Carlo ray tracing method, applied at the photoreactor scale. This approach allows to account for important design parameters, such as photocatalyst layer thickness, location of supporting surfaces, and incoming radiation profiles, among others. To resolve the validity of the characteristic matrix method for the description of the optical properties of the catalyst, modeled transmittance and reflectance of the supported films is compared to experimental data. This comparison is carried out for different wavelengths and film thicknesses. Afterwards, the model is applied to a solar reactor with anatase catalyst films supported on multiple surfaces.

The reactor consists of a compound parabolic concentrator with a tubular borosilicate glass receiver. Smaller glass tubes coated with the catalyst are located inside this receiver. With the developed model, a study is conducted to analyze the reactor optical performance as a function of two important design variables: film thickness and radius of the absorber tubes. The results of the model indicate directions for the improvement of the current design.