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The main advantages of the organic-inorganic halide perovskite solar cell technology are high efficiencies achieved after short development time in combination with rather simple solution-based processing. In this paper, we address remaining challenges by presenting a low-temperature two-step hybrid evaporation-spincoating method that combines high reproducibility with easy fabrication and high stabilized efficiencies, which is compatible with the processing of pervoskite silicon tandem solar cells and avoids using hazardous solvents such as dimethylformamide and dimethylsulfoxide. Lead iodide (PbI 2 ) is thermally evaporated and subsequently converted into a compact crystalline perovskite layer by methylammonium iodide spincoating. Moreover, the role of the interface passivation between perovskite absorber and electron transport layer on crystallization and optoelectronic properties of the perovskite absorber is investigated within a systematic thickness and concentration variation of [6, 6]-phenyl-C 61 -butyric acid methyl ester passivation layer and by analyzing charge extraction with spatial and time resolved photoluminescence measurements. With an optimized charge extraction, 18.2% stabilized efficiency under one sun illumination is achieved. This is the highest value reported so far for the single junction perovskite solar cells made by a two-step hybrid evaporation-spincoating method.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 1268-1271, We present an in-depth theoretical analysis of nanostructured antireflection coatings (ARCs) for broadband and omnidirectional operation in III-V multijunction solar cells. We analyse the performance of nanostructured ARCs within three different models, namely an effective medium with a gradual variation of the average refractive index, a periodic nanostructure, and a fully random nanostructure. We show that the effective medium structure generally outperforms the periodic and random ones, while the three models agree well with each other when the length scale of the nanostructures is much smaller than the wavelength of visible light. We discuss the expected improvement over the performance of the present “standard” ARC structure based on SiO2/Ta2O5 bilayers.

31st European Photovoltaic Solar Energy Conference and Exhibition; 117-120, It is currently possible to fabricate crystalline silicon solar cells with the absorber thickness ranging from a few hundreds of micrometres (conventional wafer-based cells) to devices as thin as 1 μm. In this work, we use a model single-junction solar cell to calculate the limits of energy conversion efficiency and estimate the optimal absorber thickness. We analyse the roles of bulk and surface recombination mechanisms. Considering the main parameters that impact the solar cell performance, we quantify the requirements for achieving a given efficiency, which helps us to establish a proper design strategy for high efficiency silicon solar cells. Finally, we review an analytic electro-optical model of silicon solar cells, which is a reliable alternative to more complex device simulators.

29th European Photovoltaic Solar Energy Conference and Exhibition; 210-213, In this work, we use a rigorous electro-optical model to study silicon solar cells with random textures. First, we calculate the efficiency limits of silicon solar cells by considering a p-n junction and solving the driftdiffusion equations as a function of the cell thickness, assuming the Lambertian light trapping. Second, we aim to design realistic solar cells to get as close as possible to the efficiency limits. We use an efficient numerical model, which allows us to study a wide range of the absorber thickness and material parameters. We theoretically demonstrate how to simultaneously increase short-circuit current and improve open-circuit voltage by, respectively, texturing the front surface and decreasing the absorber thickness.

29th European Photovoltaic Solar Energy Conference and Exhibition; 123-126, The key advantage of a thin absorbing layer in solar cells is related to reduced electrical transport losses. Yet, decreasing the absorber thickness significantly reduces absorption of sunlight. In this regard, engineering the geometry of substrate allows one to trap the light within a physically thin layer and maximize the absorption. In this work, we experimentally investigate the scattering properties of one-dimensional rough substrates that provide strong and broad-band absorption enhancement. We demonstrate that these substrates have superior scattering properties with respect to the commonly used Asahi-U textures. In particular, we focus on Angular Resolved Scattering (ARS) of transmitted light and haze (i.e., the ratio of the intensity of scattered light to the total intensity of light transmitted through the texture). Finally, we compare the experimental results with the numerical simulations, obtaining a good agreement.

28th European Photovoltaic Solar Energy Conference and Exhibition; 233-236, In this work we focus on randomly rough textures for light-trapping in thin-film silicon solar cells. We use a simple but accurate model of Gaussian roughness, and with rigorous calculations we demonstrate that optimized rough textures allow to approach the Lambertian Limit of absorption. These results are explained by a detailed analysis of the roughness optical properties, which can be easily correlated with the absorption enhancement in the solar cell absorber. Finally, we compare structures based on crystalline and microcrystalline silicon, to investigate the role of light-trapping as a function of size and nature (direct or indirect) of the energy band gap.

27th European Photovoltaic Solar Energy Conference and Exhibition; 491-496, We theoretically investigate light trapping in thin film crystalline silicon solar cells with ordered and disordered photonic structures using the Rigorous Coupled Wave Analysis formalism. The general aspects of these two complementary optical designs are presented, focusing on the absorption in the active material and on the resulting photo generated current, which are assumed as the figures of merit. A comparison with the Lambertian limit to light trapping for the 1D and 2D cases is performed. We show that the diffraction of light and the improved impedance matching are responsible for the increased efficiency of the photonic devices. These effects are first investigated in ordered 1D and 2D photonic patterns and in 1D rough scattering surfaces, which are assumed as prototypes for pure ordered and disordered systems. We then propose a final design consisting of a 1D lattice with engineered size and position disorder to take advantage of both the approaches. The resulting structures show a broad band absorption enhancement, which results in higher photocurrent and it is very close to the 1D Lambertian limit. These results point out that an engineered combination of order and disorder is the optimal solution in terms of optical design.

27th European Photovoltaic Solar Energy Conference and Exhibition; 2334-2337, In view of large-scale exploitation of CuIn1-xGaxSe2 (CIGS) solar cells for photovoltaic energy conversion, it would be quite important not only to increase the conversion efficiency, but also to reduce the thickness of CIGS layer in order to decrease the use of rare and expensive elements, especially Indium. In this work we perform a full study of optical properties of CIGS solar cells grown by a hybrid sputtering/evaporation process, and use the resulting optical functions for electro-optical simulations. We then introduce a texturization of the interfaces and investigate the effects of light trapping on the conversion efficiency. Starting from a CIGS thickness around 2 μm, we show that the same or even higher efficiency can be achieved with much reduced film thickness, with a sizeable effect due to the photonic structure.

26th European Photovoltaic Solar Energy Conference and Exhibition; 259-263, We present an experimental study of multilayer luminescent solar concentrators (LSCs) based on spectroscopic characterization and external quantum efficiency measurement, which is assumed as figure of merit for this work. We focus on two types of LSCs: polymeric and liquid-based. Our aim is to study the photovoltaic conversion of solar energy by means of solar spectrum splitting by the LSC, to evaluate the effects of dyes’ concentrations on absorption of sunlight and on self-absorption of emitted fluorescence, and finally to evaluate the effects of LSCs’ sizes on their performance. Single-layer and bi-layer LSCs are considered, based on one or more types of fluorescent dyes.

25th European Photovoltaic Solar Energy Conference and Exhibition / 5th World Conference on Photovoltaic Energy Conversion, 6-10 September 2010, Valencia, Spain; 517-519, We present a theoretical study of amorphous and crystalline thin-film solar cells with a periodic pattern on a sub-micron scale realized in the silicon layer and filled with silicon dioxide right below a properly designed antireflection coating. The study and optimization of the PV structure as a function of all the photonic crystals parameters allows to identify the different roles of the periodic pattern and of the etching depth in determining an increase of the absorption. From one side, the photonic crystal acts as an impendence matching layer, thus minimizing reflection of incident light over a particularly wide range of frequencies. Moreover a strong absorption enhancement is observed when the incident light is coupled into the quasi guided modes of the photonic slab. We compare the efficiency of this structure to that of PV cells characterized by the sole antireflection coating. We found a substantial increase of the short-circuit current when the parameters are properly optimized, demonstrating the advantage of a wavelength-scale, photonic-crystal based approach.

During the past decade, there has been a tradition of comparing the current state-of-the-art optical mode solvers from time to time [1]. In the framework of the European COST P11 action [2], we performed such a comparison, but this time with an additional complication, namely the modeling of an extremely small loss in the propagation constant due to substrate leakage. We present results from a wide variety of models, ranging from different finite-elements solvers, effective index and perturbation methods, fourier modal methods and film mode matching methods.

International audience

International audience

International audience; The static dielectric properties of (001)(GaAs)p/(AlAs)p superlattices have been calculated as a function of their period p for 1≤p≤12, starting from density-functional theory. The interplay between quantum confinement and local field effects is shown to be crucial. For light polarized in the growth direction it leads to the otherwise surprising justification of the use of a classical effective medium theory, even for the smallest periods. Only the inclusion of both contributions allows in ab initio and in semiempirical calculations to reproduce the experimentally observed birefringence.