In this paper previously developed combined model of non-conformal layer growth is used to calculate positions in thin-film silicon solar cells where defective regions are expected to be formed within semiconductor layers, depending on the substrate texture. This enables omission of the textures leading to cells of poor electrical quality in the early process of optical optimisation of the cells and substrate texture design. Coupled with three-dimensional rigorous optical simulations, substrate textures are optimised with respect to high short-circuit current and defectless layer growth in micromorph silicon solar cells. Firstly, the approach of determination of defective regions is validated on realistic structures. Secondly, analysis of the effects of texture shape and of the material and the thickness of the grown layer is carried out. Thirdly, optimisation of substrate texture for micromorph type of solar cell is performed for sinusoidal, widened and semi-circular textures. Results on widened textures show, that smoothing/widening of the valleys does not always suppress the formation of defective regions in μc-Si:H and a-Si:H layers. A semi-circular type of the texture is determined to be the most appropriate for defectless absorbers in the analysed micromorph solar cells in substrate configuration, resulting also in up to 85% increase in short-circuit current density of the bottom cell.
COBISS.SI-ID: 10867540
A ceramic target with Ga:In:Sn=4:64:32 metal ratio has been sintered and used for RF sputtering process to develop high quality Ga doped ITO (GITO) transparent conductive oxide layers, particularly for photovoltaic applications. The sputtering parameters (sputtering power, oxygen flow, and substrate temperature) have been varied first and optimized with respect to the resistivity measurements. The layers deposited under optimized conditions were then post-annealed at different temperatures (200−500 ⁰C) either in the air or in nitrogen atmosphere in order to further improve the conductivity. The deposited 200 nm thick GITO layer has high electron mobility (50 cm2/Vs) at relatively low resistivity (0.90 mΩcm) although the free electron concentration is kept low (1,4e20 cm-3) to prevent excessive free-carrier absorption. Thus, high transmission of the layer (~80% at 400−1500 nm) is obtained.
COBISS.SI-ID: 29163815
In the first part a review of methods and simulators in the field of optical modeling and simulations of thin-film solar cells is given. We introdiuce an idea of a coupled modeling approach. We show simulation results of rigorous optical simulations of Si solar cells including nanotextures, employing a model of realistic layer growth. Furthermore, simulations of organic solar cells including macrotextures were carried out with simulator CROWM.
COBISS.SI-ID: 10835540
In optoelectronic and photovoltaic devices, transparent conductive oxides are important in establishing a good electrical contactwhile minimizing optical losses over a broad range of wavelengths (400–1200nm). To date, research has focused on In2O3-SnO2 (ITO) films. In this paper, we report on a study of Ga-doped ITO (GITO) films, which in contrast to standard ITO 90/10 (i.e. In:Sn=90:10) films contain less In. Initially, we describe the development of a multi-component Ga-In-Sn oxide target with a Ga:In:Sn ratio of 4:64:32, which was used in a radio-frequency sputtering system to deposit GITO thin films on glass substrates. Furthermore, we describe the micro-structural/structural (scanning electron microscopy and X-ray diffraction spectroscopy), optical (wavelength dependent complex refractive indices) and electrical (resistivity, mobility, free carrier density) measurements used to optimize sputtering conditions and post-annealing processing. As well as achieving an optimized/improved GITO thin film deposited at high substrate and annealing temperatures, we obtained promising thin GITO films with excellent optical properties and with relatively low resistivity (1.7mΩcm) deposited and annealed at temperatures around 200 °C.
COBISS.SI-ID: 11620180
Surface textures in thin-film silicon multi-junction solar cells play an important role in gaining the photocurrent of the devices. In this paper, a design of the textures is carried out for the case of amorphous silicon/micro-crystalline silicon (a-Si:H/μc-Si:H) solar cells, employing advanced modelling to determine the textures for defect-free silicon layer growth and to increase the photocurrent. A model of non-conformal layer growth and a hybrid optical modelling approach are used to perform realistic 3D simulations of the structures. The hybrid optical modelling includes rigorous modelling based on the finite element method and geometrical optics models. This enables us to examine the surface texture scaling from nanoto macro-sized (several tens or hundreds of micrometers) texturisation features. First, selected random and periodic nanotextures are examined with respect to critical positions of defect-region formation in Si layers. We show that despite careful selection of a well-suited semi-ellipsoidal periodic texture for defect-free layer growth, defective regions in Si layers of a-Si: H/μc-Si:H cell cannot be avoided if the lateral and vertical dimensions of the nano features are optimised only for high gain in photocurrent. Macro features are favourable for defect-free layer growth, but do not render the photocurrent gains as achieved with light-scattering properties of the optimised nanotextures. Simulation results show that from the optical point of view the semi-ellipsoidal periodic nanotextures with lateral features smaller than 0.4 μm and vertical peak-to-peak heights around or above 0.3 μm are required to achieve a gain in short-circuit current of the top cell with respect to the state-of-the-art random texture ()16% increase), whereas lateral dimensions around 0.8 μm and heights around 0.6 μm lead to a )6% gain in short-circuit current of the bottom cell.
COBISS.SI-ID: 11347796