Crystalline silicon thin-film solar cells have the potential to drastically reduce the cost for silicon solar cells. The aim of the work described in this book was to improve the quality of thin silicon layers on foreign substrates and to apply the experience gained hereby to various low-cost substrates. Two aspects of the crystalline silicon thin-film solar cell were examined intensively to reach this goal: diffusion barrier properties of common intermediate layers, and zone-melting recrystallisation of silicon layers. For investigation of diffusion barrier layers, the focus was set to diffusion of the transition metals iron, chromium and vanadium in the intermediate layer materials SiO2 and SiNx deposited by plasma-enhanced chemical vapour deposition. Temperatures ranging from 900C to 1350C were applied to the samples. Zone-melting recrystallisation of silicon is an important technique to prepare large crystal grains of several millimetres width and several centimetres length on amorphous substrates. Parameter studies on SiO2-capped multicrystalline silicon wafers were done to investigate the effect of the so-called supercooled zone on crystal quality. One-side contacted solar cells were prepared on optimised layers on such model substrates. For the first time, also low-cost ribbon silicon and ceramics (SiSiC, Si3N4, SiAlON, mullite) were tested as substrate material. Cell efficiencies up to 10.5% could be obtained when using these materials. The author: Dr. Stefan Reber studied Physics at the Technical University of Darmstadt, Germany. He joined the solar cell department of the Fraunhofer Institute for Solar Energy Systems for his Ph.D. thesis, where he was in charge of improving crystalline silicon thin-film solar cells on foreign substrates.

Reported are the development and demonstration of a 17% efficient 25mm x 25mm crystalline silicon solar cell and a 16% efficient 125mm x 125mm crystalline silicon solar cell, both produced by ink-jet printing Silicon Ink on a thin crystalline silicon wafer. To achieve these objectives, processing approaches were developed to print the Silicon Ink in a predetermined pattern to form a high efficiency selective emitter, remove the solvents in the Silicon Ink and fuse the deposited particle silicon films. Additionally, standard solar cell manufacturing equipment with slightly modified processes were used to complete the fabrication of the Silicon Ink high efficiency solar cells. Also reported are the development and demonstration of an 18.5% efficient 125mm x 125mm monocrystalline silicon cell, and a 17% efficient 125mm x 125mm multicrystalline silicon cell, by utilizing high throughput ink-jet and screen printing technologies. To achieve these objectives, Innovalight developed new high throughput processing tools to print and fuse both p and n type particle Silicon Inks in a predetermined pattern applied either on the front or the back of the cell. Additionally, customized ink-jet and screen printing systems, coupled with customized substrate handling solution, customized printing algorithms, and a customized ink drying process, in combination with a purchased turn-key line, were used to complete the high efficiency solar cells.

Today’s solar cell multi-GW market is dominated by crystalline silicon (c-Si) wafer technology, however new cell concepts are entering the market. One very promising solar cell design to answer these needs is the silicon hetero-junction solar cell, of which the emitter and back surface field are basically produced by a low temperature growth of ultra-thin layers of amorphous silicon. In this design, amorphous silicon (a-Si:H) constitutes both „emitter“ and „base-contact/back surface field“ on both sides of a thin crystalline silicon wafer-base (c-Si) where the electrons and holes are photogenerated; at the same time, a-Si:H passivates the c-Si surface. Recently, cell efficiencies above 23% have been demonstrated for such solar cells. In this book, the editors present an overview of the state-of-the-art in physics and technology of amorphous-crystalline heterostructure silicon solar cells. The heterojunction concept is introduced, processes and resulting properties of the materials used in the cell and their heterointerfaces are discussed and characterization techniques and simulation tools are presented.

Thin film amorphous silicon (a-Si) is a low cost alternative to crystalline silicon wafers used in solar cells. a-Si is advantageous in that it can be deposited onto low cost substrates such as glass or flexible polymers, is scalable to large areas, and uses low processing temperatures (

The profitability of silicon solar cells is a critical point for the PV market and it requires improved electrical performance, lower wafer production costs and enhancing reliability and durability of the cells. Innovative processes are emerging that provide thinner wafers with less raw material loss. But the induced crystallinity and distribution of defects compared to the classical wafers are unclear. It is therefore necessary to develop methods of microstructural and mechanical characterization to assess the rigidity and mechanical strength of these materials. In this work, 4-point bending tests were performed under quasi-static loading. This allowed to conduct both the stiffness estimation and the rupture study. A high speed camera was set up in order to track the fracture process thanks to a 45° tilted mirror. Fractographic analysis were performed using confocal optical microscope, scanning electron microscope and atomic force microscope. Electron Back-Scatter Diffraction and Laue X-Ray diffraction were used to explore the relationship between the microstructural grains orientations/textures of our material and the observed mechanical behavior. Jointly, finite element modeling and simulations were carried out to provide auxiliary characterization tools and help to understand the involved fracture mechanism. Thanks to the experiment-simulation coupled method, we have assessed accurately the rigidity of silicon wafers stemming from different manufacturing processes. A fracture origin identification strategy has been proposed combining high speed imaging and post-mortem fractography. Fracture investigations on silicon single crystals have highlighted the deflection free (110) cleavage path, the high initial crack velocity, the velocity dependent crack front shape and the onset of front waves in high velocity crack propagation. The investigations on the fracture of multi-crystalline wafers demonstrate a systematic transgranular cracking. Furthermore, thanks to twin multi-crystalline silicon plates, we have addressed the crack path reproducibility. A special attention has been paid to the nature of the cleavage planes and the grain boundaries barrier effect. Finally, based on these observations, an extended finite element model (XFEM) has been carried out which fairly reproduces the experimental crack path.