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Herein, a process for the large‐area passivating and contacting of nanowire‐based solar cells is demonstrated. The nanowire‐based solar cells are prepared on layered laser crystallization (LLC) polycrystalline silicon (pc‐Si) thin films with thickness less than 2 μm. It is demonstrated that the space between the nanowires can be filled with a passivating dielectrics Al2O3 layer, and the nanowire tips can be exposed by a self‐regulating selective etching of the Al2O3 deposited on the tips and that on the sidewalls. The exposed tips of the nanowires can be connected by a transparent conducting aluminum‐doped zinc oxide (Al:ZnO or AZO) layer deposited by atomic layer deposition (ALD). The laser beam‐induced current mapping (LBIC) demonstrates that the current density can increase up to 63% at 633 nm due to light trapping and the superior passivation of the nanowires with an thin pc‐Si film of only 1.73 μm. [ABSTRACT FROM AUTHOR]

Double layers of deuterated and hydrogenated amorphous silicon (a‐Si:H) on glass are heated in the ambient by scanning with a green (532 nm) continuous wave laser. The hydrogen diffusion length in the laser spot is obtained from the deuterium (D)–hydrogen (H) interdiffusion measured by secondary ion mass spectrometry (SIMS), the temperature in the laser spot is obtained by calculation. Under certain conditions, detachment of the deuterated layer from the hydrogenated layer is observed in the SIMS depth profiles, visible by rising oxygen and carbon signals at the D/H interface attributed to in‐diffusion of atmospheric gas species like water vapor, oxygen, and carbon oxide. Stacks involving both undoped and boron‐doped a‐Si:H films show disintegration. The results suggest that the parameters leading to the disintegration effects are the presence of a plane of reduced material cohesion at the D/H interface, a sizeable H diffusion length and a rather high heating rate. Herein, it is likely considered that the observed layer disintegration process is involved in the peeling of a‐Si:H films upon fast heating. Furthermore, the results show that rapid laser heating can be used to detect planes of reduced material cohesion which may compromise the electronic properties of a‐Si:H‐based stacks. [ABSTRACT FROM AUTHOR]

Recently, polycrystalline silicon thin film solar cells on glass are fabricated by a laser induced liquid phase crystallization (LPC) process. This study compares a new economic diode laser, emitting a line focus at 980 nm, with the 808 nm laser normally used concerning its absorption during LPC. We measured the optical constants of amorphous silicon by spectral ellipsometry and UV/VIS spectroscopy. Together with the literature data for crystalline and liquid silicon combined with numerical temperature simulations, we calculated the absorption during LPC and the overall power needed for successful crystallization. Solar cells prepared with both laser types show comparable crystallographic and optoelectronic characteristics. Concerning the economic advantages, the use of such a 980 nm diode laser system would be the choice for the potential industrial production. Polycrystalline silicon thin film solar cells on glass are fabricated by laser-induced liquid phase crystallization. A new economic diode laser emitting a line focus at 980 nm is compared to the 808 nm laser normally used. Solar cells show comparable crystallographic and optoelectronic characteristics. [ABSTRACT FROM AUTHOR]

Liquid-phase crystallized silicon on glass (LPCSG) presents a promising material to fabricate high quality silicon thin films, e.g., for solar cells and modules. Using continuous wave line focus laser irradiation at 808 nm, about 10 μm thick microcrystalline silicon layers are fabricated by liquid-phase crystallization of amorphous or nanocrystalline silicon layers deposited by electron beam evaporation on Borofloat 33 glass. To achieve high solar cell efficiencies with such thin silicon layers, effective light trapping structures at the silicon surface are needed to enhance the light absorption and thereby the current in the solar cell. At the same time, these surface structures must provide low surface recombination velocity to maintain high open circuit voltage ( Voc). Light trapping structures in LPCSG absorber prepared by conventional KOH texturing and by nanowire structuring of the solar cell backside are investigated. The impact of structures on short circuit current density ( Isc) is determined from optical measurements. As a new approach, effective carrier lifetime is measured in LPCSG absorbers using the quasi steady-state photoconductance method to determine the impact of structuring on surface recombination and implied Voc of solar cell precursors. Carrier lifetimes in the range of 300-400 ns are measured indicating a carrier diffusion length of more than 20 μm, which is 2-3 times larger than the layer thickness. It is found that a slight pyramidal surface texture by KOH solution provides a high level of light trapping increasing Isc by 17-18% and maintaining high Voc (>600 mV). The potential for current enhancement of nanowire structuring is higher (≈20%), but further optimization of nanowire dimensions and of surface cleaning of nanowire structures is needed to overcome higher surface recombination and the resulting Voc losses. [ABSTRACT FROM AUTHOR]

During the preparation of silicon thin film solar cells on glass substrates by diode laser induced liquid phase crystallization (LPC), cracking is an issue. This is due to thermal stresses caused by high temperature gradients within the sample. In this paper, the relation between thermal stress and the temperature distribution within the sample during LPC is discussed. Experiments for two sets of laser irradiation parameters were done leading to crack free or cracked crystallization of the film. Additionally, the evolution of temperature during LPC was modeled numerically. Based on the simulation, the thermal stresses introduced were calculated. The complex viscoelastic problem was simplified to an elastic multilayer model, which can be solved analytically. The theoretical results can explain the experimental behavior. [ABSTRACT FROM AUTHOR]

This study demonstrates an innovative approach to clean a polycrystalline seed layer surface for solid phase epitaxy of amorphous silicon (a-Si). The excimer laser cleaning (ELC) makes use of in situ excimer laser irradiation during the first stages of a-Si deposition leading to melting of the as deposited a-Si and parts of the seed layer. The increased diffusion in liquid silicon allows for 'smearing out' of surface contamination species. After liquid phase epitaxy is finished, further a-Si is deposited and crystallized by solid phase epitaxy. Thanks to the 'smearing out,' the interface between the crystalline and amorphous silicon exhibits less contamination locally. SIMS measurements demonstrate a reduced carbon concentration at the seed layer surface after ELC. Numerical simulations, taking into account heat transfer and temperature dependent diffusion, support the reduction of carbon concentration. The simulations agree very well with experimental results. To get optimal solid phase growth conditions, the a-Si deposition temperature has to be below 200 °C. Above 200 °C deposition temperature, defective growth occurs resulting in poor crystallinity or even in nonepitaxial growth. [ABSTRACT FROM AUTHOR]

Silicon nanowire (SiNW) based solar cells are a promising candidate for third generation solar cells with high efficiency, which will further reduce the cost of the PV modules, making it competitive with conventional energy sources. In this paper the wet chemical etching process for generating silicon nanowires is investigated on different low-cost substrate materials. These nanowires are useful for a radial pn-junction solar cell with core-shell configuration, which allows for using absorber materials with low-carrier lifetime. In this work, wet chemical nanowire etching is applied to edge-defined film-fed growth (EFG) mc-Si wafers, mc-Si wafers made from metallurgical grade Si, multicrystalline (mc-Si) thin films deposited on glass, and thin crystallized films deposited on mc-Si wafers produced from metallurgical grade Si. A proof of concept for using low-cost materials in PV is demonstrated for SiNWs prepared on mc-Si wafer produced from highly doped MG-Si. [ABSTRACT FROM AUTHOR]

Liquid phase crystallized (LPC) silicon thin films on glass substrates are a feasible alternative to conventional crystalline silicon (c‐Si) wafers for solar cells. Due to substrate limitation, a low‐temperature technology is needed for solar cell fabrication. While silicon heterojunction is typically used, herein, the combination of vanadium oxide/c‐Si heterojunction as emitter and base contacts defined by IR laser processing of phosphorus‐doped amorphous silicon carbide stacks is explored. LPC solar cells are fabricated using such technologies to identify their issues and advantages with a promising performance of an active‐area efficiency of 5.6%. Apart from the absence of light‐trapping techniques, the relatively low efficiency obtained is attributed to a low lifetime in the LPC silicon bulk. These poor material properties imply a short diffusion length that makes it that only photogenerated carriers in the emitter regions can be collected. Consequently, future devices should show narrower base contact regions, suggesting a shorter‐wavelength laser, combined with longer LPC substrate lifetimes. [ABSTRACT FROM AUTHOR]