Desirée Gentilini

Role of Ferroelectric Nanodomains in the Transport Properties of Perovskite Solar Cells

Metropolis Monte Carlo simulations are used to construct minimal energy configurations by electrostatic coupling of rotating dipoles associated with each unit cell of a perovskite CH3NH3PbI3 crystal. Short-range antiferroelectric order is found, whereas at scales of 8-10 nm, we observe the formation of nanodomains, strongly influencing the electrostatics of the device. The models are coupled to drift-diffusion simulations to study the actual role of nanodomains in the I-V characteristics, especially focusing on charge separation and recombination losses. We demonstrate that holes and electrons separate into different nanodomains following different current pathways. From our analysis we can conclude that even antiferroelectric ordering can ultimately lead to an increase of photoconversion efficiencies thanks to a decrease of trap-assisted recombination losses and the formation of good current percolation patterns along domain edges.

Modeling and simulation of energetically disordered organic solar cells

The aim of this work is to present a consistent model for simulation of organic solar cells (OPV) with a correct description of mobility, density of state, organic-metal contacts, and exciton. We simulate the photoconversion by means of an integration of the optical and electrical part: light absorption is calculated with a Transfer Matrix Model and the charge transport is computed using Drift Diffusion approach including the effect of energetically disorder materials. Most model parameters are directly taken from experiment. The model is used to study the effect of energetic disordered materials and cell thickness on the performance of the cell in terms of short circuit current, open circuit voltage, and fill factor. Based on the results of this model, it will be possible to design and predict the optimal thickness of OPV toward higher efficiencies.

Multiscale Modeling of Dye Solar Cells and Comparison With Experimental Data

In this paper, we investigate the electrical properties of dye solar cells (DSCs) under illumination and in dark conditions when an external bias is applied. The measurements performed on the cells will be compared with theoretical calculations. The modeling is made using two approaches: a finite-element code based on Tiber computer-aided design (CAD) software to describe in detail the electrical properties of the cell and a circuital model implemented on PSpice. The latter has been developed in the perspective of simulating larger systems, such as modules and panels. It should be a phenomenological model to fit I-V characteristics of real cells. The CAD instead allows to calculate steady-state properties and I-V characteristics of the cell, solving a set of differential equations on meshes in one, two, and three dimensions. The two models are compared to experimental values, and the microscopic model is used to shine light over the fitting parameters of the circuital model.

Systematic Study of the PCE and Device Operation of Organic Tandem Solar Cells

By combining optical and drift-diffusion models, a comprehensive simulation of power conversion efficiency of tandem solar cells is presented. To obtain consistent current-voltage characteristics of polymer tandem solar cells, the model takes into account correct description of organic-metal interfaces and organic semiconductor physics, in order to include the effect of interfaces and energetic disorder. A generalized methodology is developed to obtain the current-voltage characteristics of polymer tandem solar cells, which fully accounts for the interplay between the two subcells. The model is applied to the tandem cell with different commercially available polymers and for different subcell thicknesses and interconnection architectures. Based on the results of this model, it will be possible to design and optimize tandem structures toward higher efficiencies. Finally, it is concluded that the parallel configuration shows the highest performance over all studied cell structures.

Mesoscopic perovskite solar cells and modules

In this work we exploit the use of a new promising class of light harvesting materials, namely the hybrid organic halide perovskites (CH3NH3PbI3-xClx), for the fabrication of mesoscopic perovskite solar cells and series-connected monolithic perovskite module. To achieve this goal, important innovative procedures were implemented in order to define a reproducible fabrication path applicable also to large area devices. Small area solar cells were fabricated with both Spiro-OMeTAD and the P3HT polymer as Hole Transporting Material (HTM) both showing a Power Conversion Efficiency (PCE) up to 10.5%. First attempts to scale up the size of the cell to a module size shown a PCE of 5.1% on an active area of 13.44cm2. In order to improve the efficiency of the module, we developed a new Laser assisted patterning of the perovskite/compact layers together with an optimized perovskite deposition in controlled atmosphere. This allowed us to improve the module PCE up to 7.3% which represent the state of art efficiency for a perovskite module. A promising long-term stability was obtained for the module with Spiro-OMeTAD as HTM. Supporting simulations of Mesoscopic Perovskite Solar Cells were obtained by using the multiscale device simulator TiberCAD.

Effect of ferroelectric nanodomains in perovskite solar cells

In this work we consider the effect of ferroelectric nanodomains on hybrid CH3NH3PbI3 perovskite solar cells. Two-dimensional models of ferroelectric domains are obtained with Metropolis Monte Carlo, considering one effective rotating dipole in each crystal cell. Transport properties of perovskite samples are obtained using drift-diffusion calculations, including local polarization field. We show that the presence of nanodomains have a strong impact on transport and charge carrier separation.

Simulation of solid-state dye solar cells based on organic and Perovskite sensitizers

In this work we present a multiscale numerical simulation of solid-state Dye and Perovskite Solar Cells where the real morphology of the mesoporous active layer is taken into account. Band alignment and current densities are computed using the drift-diffusion model. In the case of Dye cells, a portion of the real interface is merged between two regions described using the effective medium approximation, casting light on the role of trapped states at the interface between TiO2 / Dye / hole transporting materials. A second case of study is the simulation of Perovskite Solar Cell where the performances of cells based on Alumina and Titania mesoporous layer are compared.

Analysis of changes in efficiency by simulating dye-sensitized solar cells varying the characteristics of TiO2

Dye Sensitized solar cells (DSC) are an interesting alternative to conventional silicon based solar cells. Although DSCs are very close to be commercialized, still many issues need to be addressed. Part of the problem is related to the lack of a reliable and consistent simulator able to catch the physics and the chemistry underlining the functioning of the cell. The need of a reliable simulator and modelling is particularly important for the engineering of the cell and to define trends not only in the component characteristics, but also in the building of the device. Among the different parts which compone a DSC the relevance of semiconductor titanium oxide substrate can hardly be underestimated. TiO2 is where the dye molecule is chemisorbed and where the recombination occurs. Moreover, changes in the topology of the semiconductor paste can lead to other smaller effects in the total efficiency. In this paper we investigate the effects of changing working parameters for the titanium oxide and varying its topology. The simulations are performed using a finite element code based on TiberCAD software1 to describe in details the electrical properties of the cell. The CAD allows to calculate steady-state properties and ideal I-V characteristics of the cell solving a set of differential equations on meshes in 1, 2 and 3 dimensions.