Thin-film Si solar cell technology is a promising photovoltaic (PV) technology for delivering low-cost solar electricity. A drawback of this technology is a relatively low stabilized efficiency of modules that varies between 5 to 10%. Light management plays a crucial role in increasing the performance of thin-film Si solar cells. Light trapping is an important part of the light management. Application of light trapping techniques in thin-film Si solar cells increases the average optical thickness of the absorber layers resulting in an enhanced absorption especially in the long wavelength region. Several recently introduced approaches for light trapping in thin-film Si solar cells will be discussed, such as: i) periodic surface textures and modulated surface textures for efficient light scattering, ii) 1-D photonic crystals as intermediate and back reflectors for selectively enhanced reflection and suppression of parasitic optical losses at the back metal contact and iii) plasmon scattering using metal nanoparticles. Application of these novel approaches in amorphous Si solar cells will be presented. Modeling of new light trapping approaches can strongly contribute to their optimization, such as surface textures and/or size and shape of metal nanoparticles. We shall show results from optical 3-D simulations of full solar cell structures that lead to the optimization of periodic interface textures.@en

Diffusive dielectric materials such as white paint have been demonstrated as effective back reflectors in the photovoltaic technology. In this work, a one-dimensional (1D) optical modeling approach for simulation of white paint films is developed and implemented in a 1D optical simulator for thin-film solar cells. The parameters of white paint, such as the paint film thickness, the pigment volume concentration (PVC), and the pigment/binder refractive index ratio (RIR), are examined and optimized to achieve the required optical properties for back reflector application. The simulation trends indicate that white paint back reflectors with sufficient film thickness and higher PVC and RIR values exhibit improved reflectivity characteristics which results in an increased long-wavelength quantum efficiency of thin-film silicon solar cells. The simulation results based on the 1D model agree very well with the experimental data obtained from reflectance measurements of various white paint compositions and quantum efficiency measurements of amorphous silicon solar cells with white paint back reflectors.@en

In thin-film silicon photovoltaic technology light management is important for achieving high efficiency of solar cells. Advanced light trapping techniques have to be employed to boost the solar cell efficiencies further. In this contribution we investigate the following advanced light trapping techniques implemented amorphous silicon solar cell: (i) periodic-like surface textures to achieve an angle-selective scattering, (ii) modulated surface textures for enhanced scattering in broad wavelength range, and (iii) one-dimensional photonic crystals used as dielectric back reflectors.@en

Optical analysis of hydrogenated amorphous silicon (a-Si:H) solar cells with a periodic texture applied to the interfaces was carried out by two-dimensional optical simulator. The optical simulator solves the electromagnetic wave equations by means of finite element method using triangular elements for the discretization of space. The periodic texture with rectangular-like shape acts as a diffraction grating which scatters light into selective angles and thus gives a potential for significant prolongation of optical paths in thin absorber layers of the cells. Optimization of the geometrical parameters (period, height and duty-cycle) of the periodic texture was carried out in order to obtain the highest photocurrent from a-Si:H solar cells. The a-Si:H solar cell with the optimal periodic texture parameters (period of 300¿nm, height of 300¿nm and duty cycle of 50%) and the absorber layer thickness of 300¿nm generates up to 35% more photocurrent in comparison to the cell with flat interfaces. The optical analysis demonstrates that the optimal periodic texture in the a-Si:H solar cell results in the best trade-off between the antireflection effect at front interfaces, light scattering efficiency and the absorption losses at realistic metal back contact.@en

In this work, we investigate the concept of transparent conductive oxide (TCO)/white paint (WP) back reflectors as an alternative to the conventional textured metal-based reflectors in thin-film silicon solar cells. The optical characterisation results show that WP back reflectors exhibit good reflectivity and excellent light scattering properties which can lead to enhanced light confinement within the thin absorber layers of the cell. To confirm this, ZnO:Al/WP reflectors with WP films of different pigment volume concentration and thickness are tested in thin-film amorphous silicon solar cells. The external quantum efficiency measurements indicate that by employing ZnO:Al/WP reflectors, good solar cell performance can be achieved, which is comparable to the performance of the cell with the conventional TCO/Ag reflector. Finally, optical simulations are employed to study the potential for further improvements in cell performance as a result of the optimisation of TCO/WP reflectors.@en

A concept of a modulated one-dimensional photonic-crystal (PC) structure is introduced as a back reflector for thin-film solar cells. The structure comprises two PC parts, each consisting of layers of different thicknesses. Using layers of amorphous silicon and amorphous silicon nitride a reflectance close to 100% is achieved over a broad wavelength region (700¿1300 nm). Based on this concept, a back reflector was designed for thin-film microcrystalline silicon solar cells, using n-doped amorphous silicon and ZnO:Al. Simulations show that the short-circuit current of the cell with a modulated PC back reflector closely resembles that of a cell with an ideal reflector. ©2009 American Institute of Physics@en