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

Due to the increasing complexity of thin-film silicon solar cells, the role of computer modeling for analyzing and designing these devices becomes increasingly important. The ASA program was used to study two of these advanced devices. The simulations of an amorphous silicon solar cell with silver nanoparticles embedded in a zinc oxide back reflector demonstrated the negative effect of the parasitic absorption in the particles. When using optical properties of perfectly spherical particles a modest enhancement in the external quantum efficiency was found. The simulations of a tandem micromorph solar cell, in which a zinc oxide based photonic crystal-like multilayer was incorporated as an intermediate reflector (IR), demonstrated that the IR resulted in an enhanced photocurrent in the top cell and could be used to optimize the current matching of the top and bottom cell.@en

The scattering properties of transparent conductive oxide (TCO) layers are fundamentally related to the performance of thin film silicon solar cells. In this study we introduce an experimental technique to access light scattering properties at textured TCO-silicon interfaces. Therefore we prepared a sample with a polished microcrystalline silicon layer, which is deposited onto a rough TCO layer. We used the measured results to validate calculations obtained with rigorous diffraction theory, i.e. a numerical solution of Maxwell's equations. Furthermore we evaluated four approximate models based on the scalar scattering theory and ray tracing and compared them to the rigorous diffraction theory.@en

We present a full scattering model for nano-textured interfaces as they are present in thin film silicon solar cells. The model is based on the scalar scattering theory and predicts measured scattering parameters well.@en

An accurate characterization method is developed to determine the refractive index of smooth and surface-textured transparent conductive oxide (TCOs) films. The properties are obtained from simultaneous fitting of simulated specular reflectance/transmittance spectra to spectroscopic measurements for different polarizations and angles of light incidence. The simulations are based on a combination of physical models describing dielectric function of TCO films. Besides the refractive index also other material properties of TCO films are obtained, such as the band gap and free carrier absorption. A light scattering model is implemented into the simulations to take into account the diffused part of the light scattered at randomly-textured surfaces of TCO films.@en

Textured interfaces in thin-film silicon solar cells improve the efficiency by light scattering. A technique to get experimental access to the angular intensity distribution (AID) at textured interfaces of the transparent conductive oxide (TCO) and silicon is introduced. Measurements are performed on a sample with polished microcrystalline silicon layer deposited onto a rough TCO layer. The AID determined from the experiment is used to validate the AID obtained by a rigorous solution of Maxwell¿s equations. Furthermore, the applicability of other theoretical approaches based on scalar scattering theory and ray tracing is discussed with respect to the solution of Maxwell¿s equations.@en

The angular intensity distribution (AID) is a major parameter for evaluating scattering of light by surface-textured thin films. We discuss how the AID can be determined in the near ultraviolet, the visible and the near infrared and evaluate the used method by comparing the obtained measurement results to the results obtained with other methods. Measuring the AID in a broad wavelength range is of great use for the solar cell community, because textured thin films are widely used to enhance the photocurrent in thin-film solar cells.@en

Recent developments on scattering models based on the scalar scattering theory allow to estimate the angular intensity distribution and the haze in both transmission and reflection for nano-textured interfaces created by arbitrary materials. In this contribution, such a scattering model is combined with the opto-electric ASA simulation software and tested by simulating and measuring the external parameters and the external quantum efficiency of solar cells with different interface morphologies. This test shows that the scattering model is able to predict the influence of the nano-textured interfaces on the solar cell performance. The achievements presented in this manuscript can be used to search for nano-textured interfaces with optimized morphologies.@en

Photon management is one of the key issues for improving the performance of thin-film silicon solar cells. An important part of the photon management is light trapping that helps to confine photons inside the thin absorber layers. At present light trapping is accomplished by the employment of the refractive-index matching layers at the front side and the high-reflective layers at the back contact of the solar cells and scattering of light at randomly surface-textured interfaces. In this article key issues and potential of light management in thin-film silicon solar cells are addressed. Novel approaches for light trapping are presented such as i) surface textures based on periodic diffraction gratings and modulated surface morphologies for enhanced scattering and anti-reflection, ii) metal nano-particles introducing plasmonic scattering, and iii) one-dimensional photonic-crystal-like structures for back reflectors.@en

Light trapping in state-of-the-art thin-film silicon solar cells is accomplished by scattering of light at rough interfaces. Further enhancement of light absorption in the absorber layers can be achieved by optimizing the scattering via designing the morphology of these interfaces. The haze parameter and the angular intensity distribution of the scattered light were measured. The angular intensity measurements were carried out with variable angle spectrometry, allowing wavelengths in the visible and near infrared range. The measurements revealed new insights regarding the strong effects of the substrate surface roughness and morphology on the wavelength dependent variations of the angular intensity distribution.@en