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We present optoelectronic properties of liquid phase crystallised silicon (LPC Si) thin-film solar cells on abrade-textured glass. On the textured glass-Si interface, LPC Si film exhibits a large broadband absorption enhancement, compared to a planar reference. However, LPC Si solar cells on the textured glass demonstrate a significant electrical degradation. External quantum efficiency (EQE) for the cell on the textured glass is lower throughout the 300–1100 nm wavelength region, compared to the planar reference. Open-circuit voltage (Voc) and short-circuit current density (Jsc) for the cells on the textured glass also show lower performance. This is believed to be due to higher effective area of poorly-passivated glass-Si interface, lower bulk carrier diffusion length in the absorber material and shunting through cracks and pinholes in the LPC films on the textured glass.

This work reports a laser firing technique applied to completed silicon heterojunction interdigitated back contact solar cells in order to lower contact resistance. Previously, the implementation of a-Si:H(i) at the electron contact of polycrystalline silicon solar cells on glass substrates led to an increase in series resistance. The cell architecture with the current record efficiency of 14.2% (with illumination through glass) utilizes only an a-Si:H(n+) layer and 2–2.9 mA cm−2 of short circuit current density is lost due to electrical shading under the electron contact [1,2]. The goal of implementing an a-Si:H(i) layer and laser firing at this contact is to achieve low contact resistance at fired spots while preserving a-Si:H(i) passivation in unfired regions. After the laser firing, VOC was retained, while up to 14% absolute increase in FF was obtained with a mere 0.2 mA cm−2 loss in JSC. In the best performing cell, a 72.1% FF was achieved with a 0.7 mA cm−2 loss in JSC. Two laser sources were used to first ablate a part of the silver contact metal, and then to laser fire through the Si(n)/a-Si:H(i/n+)/ITO/Ag contact. The optimal laser fluence was found to be 1.1–0.5 J cm−2 (355 nm, picosecond pulse duration) and 4.4–5.2 J cm−2 (532 nm, nanosecond pulse duration), respectively. The upper limit on specific contact resistance in the laser fired spots was calculated to be 38 ± 20 mΩ cm 2 as a conservative estimate.

We present a detailed analysis of the photo-current potentials and losses in thin film crystalline silicon solar cells on glass. The effects of texturing the silicon backside, applying a diffuse back reflector and a textured anti-reflection foil were analysed. Light beam induced current measurements were used to determine the losses due to local effects like the absorber contact, cracks in the absorber and grain boundaries. Detailed loss analysis in combination with ray-tracing simulations showed that the maximum light trapping potential imposed by geometrical optics has nearly been achieved. The photocurrent losses due to incomplete carrier collection and parasitic absorption were accounted for using a theoretical model. For the investigated, textured, n-doped cell with reflector and anti-reflection foil, the short circuit current density ( J SC ) was 28.9 mA/cm 2 and the main loss factors were direct reflection (3.4 mA/cm 2 ), electrical shading effects due to the absorber contact (3.1 mA/cm 2 ) and incomplete carrier collection due to surface/bulk recombination (1.6 mA/cm 2 ). Using the presented light trapping scheme we obtained the following efficiencies: 11.8% for a p-doped and 12.1% for an n-doped crystalline silicon absorber. Finally, the potentials for efficiencies beyond 14% are discussed.

Liquid-phase crystallization (LPC) has proven to be a suitable method to grow large-grained silicon films on commercially well-available glass substrates. Zone-melting crystallization with high-energy-density line sources such as lasers or electron beams enabled polycrystalline grain growth with wafer equivalent morphology. However, the electronic quality is strongly affected by the material used as the interlayer between the glass and the silicon absorber. Open-circuit voltages above 630 mV, and efficiencies up to 11.8% were demonstrated using n-type absorbers on a sputtered interlayer comprising a triple stack of SiO2/SiN $_{x}$ /SiO2. In this study, we present our results to further improve the device performance by investigating the influence of the interlayer on the open-circuit voltage of the devices and characterize the properties of the absorber and interface using bias light-dependent quantum efficiency data and transmission electron microscopy (TEM) images. Finally, we investigate the applicability of aluminum oxide (Al2 O3) for passivation of p-type LPC absorbers.

Liquid phase crystallization of silicon is a promising technology to grow crystalline silicon thin films on glass. It has already been demonstrated that open circuit voltages of up to 656 mV and efficiencies of up to 11.8% can be achieved by this technique. Nevertheless further improvements are required to become competitive with wafer based silicon solar cells. A possibility to improve the quality is to enlarge the grain size and to control the crystallographic orientation of the resulting layers. While a preferential {100} surface orientation can be triggered utilizing suitable crystallization parameters, the in-plane orientation still remains random. Also the grain size stays within the same range. By introducing a local monocrystalline seed at the beginning of the crystallization process, we are able to control both the surface and the in-plane orientation of the silicon films. In addition the grain size is significantly increased in scanning direction and only limited by the substrate size of 5 cm. This high morphological quality is accompanied by an improved electrical quality confirmed by photoluminescence imaging and Hall measurements. This is a big step towards the final goal to directly grow monocrystalline silicon thin films on glass substrates.

We investigate the influence of the barrier type and the absorber doping on the open-circuit voltage of liquid phase-crystallized silicon solar cells on glass. It was found that the use of n-type instead of p-type substrates is the major reason for the recently reported boost of the open-circuit voltage ( $V_{\rm OC}$ ) up to values of 656 mV, which is by far exceeding the previously reported $V_{\rm OC}$ values of crystalline silicon solar cells on glass. Despite the high doping, locally, an internal quantum efficiency of $\text{90\%}$ can be achieved. Therewith, efficiencies of $\text{16\%}$ and up should be possible.

Liquid phase crystallization of 10 μm thin silicon layers on glass substrates was performed with a line-shaped continuous wave laser beam. The process window was investigated in terms of the scanning velocity of the laser, the pre-heating of the specimens and the applied laser intensity. We have identified the entire process window, in which large-scale crystallization without deformation or destruction of the substrate and cracking of the silicon layer can be obtained. The grain orientations of the resulting Si layers were analyzed using both electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). The influence of the critical crystallization parameters on the grain orientation of the silicon film was examined. EBSD and XRD measurements show that a preferential {100} surface texture and {100} and {101} orientations in scanning direction of the laser can be achieved if appropriate crystallization parameters are used. This texture formation is accompanied with a substantial decrease of high angle grain boundaries.

Liquid-phase crystallization (LPC) using line-shaped energy sources such as laser or electron beam has proven to be a suitable method to grow large grained high-quality silicon films onto commercially well-available glass substrates. In this study, we compare cw-diode laser-crystallized absorbers with electron beam-crystallized material using backcontacted backjunction so- lar cells. Furthermore, the influence of the absorber doping con- centration thickness on the solar cell performance is studied. Using experimental data obtained on test structures, as well as solar cells and 1-D device simulations, an ideal dopant concentration is deter- mined to be 2 − 6 × 10 16 cm −3 , in combination with an absorber thickness of 10-20 μm. Finally, we present a slightly modified cell process to reduce the optical losses, which resulted in conversion efficiencies of up to 11.8%.

Liquid phase crystallization of silicon is a promising technology platform to grow multi crystalline silicon thin films on foreign substrates. For solar cell application it has already been demonstrated that open circuit voltages of up to 661 mV [1] and efficiencies of up to 15.9% [2] can be achieved on a silicon layer of a few microns only. However, while the quality of the material has been continuously improved, the cost factor of the utilized substrate has been given little attention. The present work focuses on the technology transfer from technical glass substrates to low cost soda-lime glass substrates to become more attractive for commercial applications. We demonstrate that despite a large difference in the expansion coefficient between soda lime glass and silicon absorber layer, adhesive silicon thin films can be produced under certain conditions. On these first layers, we were able to fabricate solar cells, which in their cell and material properties were only ~30% below the values of their technical glass counterparts.