Porous TiO2 films are a crucial part of mesostructured solar cells (MSCs), both dye-sensitized solar cells (DSSCs) and perovskite solar cells (PSCs). However, the literature does not provide a clear description of the optical properties especially of the refractive index and scattering for those films relevant to MSCs. In DSSCs, two different porous TiO2 layers are included, the mesoporous active layer and the blocking layer. While the first is essential for the charge separation, electron collection and ion conduction, the second is intended for suppressing the loss of generated electrons to the electrolyte. Both layers consist of the same chemical compound, TiO2, but they have different porosities. For PSCs, the perovskite is deposited on a mesoporous TiO2 structure for enhancing the I–V characteristics
This paper investigates TiO2 films really used in fabricated MSCs. We utilize a technique allowing the determination of the effective refractive index and the film porosity for two different film kinds fabricated using sol-gel methods, discussed in our previous work, to determine the thickness of TiO2 films typically used in fabricating MSCs.
Thin film solar cells (TFSCs) where first introduced as a low cost alternative to conventional thick ones. TFSCs show low conversion efficiencies due to the used poor quality materials having weak absorption capabilities and to thin absorption layers. In order to increase light absorption within the active layer, specially near its absorption edge, photon management techniques were proposed. These techniques could be implemented on the top of the active layer to enhance the absorption capabilities and/or to act as anti-reflecting coating structures. When used at the back side, their purpose is to prevent the unabsorbed photons from escaping through the back of the cell.
In this paper, we coupled the finite difference time-domain (FDTD) algorithm for simulating light interaction within the cell with the commercial simulator Comsol Multiphysics 4.3b for describing carrier transports. In order to model the dispersive and absorption properties of various used materials, their complex refractive indices were estimated using the Lorentzian-Drude (LD) coefficients. We have calculated the absorption profile in the different layers of the cell, the external quantum efficiency and the power conversion efficiency achieved by adding dielectric nanospheres on the top of the active layer. Besides that, the enhancement observed after the addition of dielectric nanospheres at the back side of the active layer was computed. The obtained results are finally compared with the effects of using textured surface and nanowires on the top in plus of cascaded 1D and 2D photonic crystals on the back.
A comparison between Silicon (Si) which is an indirect band-gap semiconductor and Gallium Arsenide (GaAs) as a
direct band-gap semiconductor for vertical-aligned nanowire radial pn junction-based photovoltaic (PV) devices is
presented. The study takes place through determining the fill factor, the power conversion efficiency, the optimum
device length and the spectrum of the quantum efficiency. The sensitivity of both Si and GaAs nanowire to temperature
variations is also investigated. Finally, the array effect for nanowires of each material alone then of arrays of mixed
elements' types is simulated. The results are found to be in accordance with the available experimental measurements.