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Abstract

Future smart green buildings can utilize sun irradiance not only at the roof or at the building walls but also through using photovoltaic windows. In this thesis, the fabrication of semi-transparent as well as efficient solar cells is a target. We utilize mesostructured solar cells (MSSCs), where mesoporous TiO₂ plays an important role. Porous TiO₂ films are a crucial part of dye-sensitized solar cells (DSSCs) and most perovskite Solar Cells (PSCs). However, the literature does not provide a clear description of the optical properties especially of the refractive index for those films relevant to MSSCs. The first part of this thesis investigates TiO₂ films really used in fabricated MSSCs. We introduce a technique allowing the determination of the effective refractive index and the film porosity for two different film kinds fabricated using sol-gel methods. The scattering effects are investigated and turn out to be describable by either a wavelength-independent effective scattering parameter or by effective scattering particles with a defined effective scattering particle radius.
In the second part we utilize the DSSC technology in fabricating semi-transparent cells. In DSSCs, the thickness of the active layer can tune the transparency of the cell. Accordingly, a trade-off between the transparency and the cell’s efficiency is established. Taking into consideration that most of the incident light is diffused light; a new figure of merit is introduced to evaluate the performance of the DSSCs, named “TED efficiency.” The proposed TED parameter (i.e. the Transparency, conversion Efficiency and Diffused light efficiency) is not only used for evaluating the cell conversion efficiency, but also considers the visible transparency as well as the cell performance under diffused light. A 36%-transparent DSSC has been fabricated by reducing the thickness of the porous TiO₂ layer. For boosting the TED efficiency of the semi-transparent DSSC, an opaline SiO₂ layer is used. The proposed layer showed better forward scattering, acts as an UV protecting layer and colorizes the semi-transparent cell in a decorative manner. A 25% enhancement in TED efficiency was recorded for the scattering enhanced DSSC with respect to the standard DSSC as well as to the semi-transparent cell.
Finally, two-dimension colloidal crystals utilized in enhancing DSSC performance have been investigated. Despite the relative simplicity in fabricating self-assembled two-dimensional colloidal crystals, disorder is commonly observed in all reported samples regardless the nanosphere concentration in the suspension or the used solvents. Such observed disorders influence the optical behavior of the structures as well as add more challenges in the optical modeling process. Here, we are investigating the possibility for a precise disorder model through developing an algorithm capable of simulating a monolayer of SiO₂ using a kind of stochastic true-to-shape parameterization. The proposed model is seeded with structural parameters extracted from SEM measurements using real samples utilized in enhancing the efficiency of mesostructured based solar cells. Optical modeling was then conducted using finite difference time domain simulation platform. A nearly perfect matching was observed between simulated data and UV-Vis-NIR spectrometer measurements.
This thesis would be of interest for a broad readership including theoreticians and experimentalist dealing with semi-transparent as well as MSSCs solar cells. It combines a useful experimental procedure with the discussion of a new figure of merit to evaluate the performance of semi-transparent cells used in photovoltaic windows.