Firat Es

Application of Si Nanowires Fabricated by Metal-Assisted Etching to Crystalline Si Solar Cells

Reflection and transmission through a solar cell can be significantly reduced using light-trapping structures. This approach can be applied to both crystalline and thin-film solar cells to improve the light absorption and conversion efficiency of the cell. In this study, vertically aligned Si nanowires were fabricated over a large area via a metal-assisted etching technique. Following a detailed parametric study, nanowires were applied to industrial-size (156 mm × 156 mm) Si solar cells. The reflectivity from the device surface was reduced to less than 5% for the entire visible spectrum (350-750 nm), including the blue-violet region. Standard solar cell fabrication procedures were employed to fabricate cells with and without Si nanowires, and the results showed that the efficiencies of solar cells with nanowires were similar to those of standard pyramid-textured cells, revealing the potential of the proposed concept. A systematic study of the dependence of the solar cell parameters on the length of the nanowires was performed. The quantum efficiency of the cells exhibited relatively poor performance in the blue-ultraviolet range of the spectrum, and enhancement in carrier generation was observed in the red-infrared region especially for shorter nanowires.

Effect of surface type on structural and optical properties of Ag nanoparticles formed by dewetting

Integration of an array of Ag nanoparticles in solar cells is expected to increase light trapping through field enhancement and plasmonic scattering. Requirement of Ag nanoparticle decoration of cell surfaces or interfaces at the macro-scale, calls for a self-organized fabrication method such as thermal dewetting. Optical properties of a 2D array of Ag nanoparticles are known to be very sensitive to their shape and size. We show that these parameters depend on the type of the substrate used. We observe that the average nanoparticle size decreases with increasing substrate thermal conductivity and nanoparticle size distribution broadens with increasing surface roughness.

An Alternative Metal-Assisted Etching Route for Texturing Silicon Wafers for Solar Cell Applications

Metal-assisted etching (MAE) can be used to form antireflective and light-trapping structures on crystalline silicon solar cells. This method has been widely used to form nanowires and nanoholes on their surfaces. In this study, the MAE technique with additional hole-injection mechanisms has been investigated to form surface nanostructures with various shapes. The effect of each chemicals percentage, as well as the etching time, has been studied on the surface geometry and optical performance. The average reflection from the surface was reduced to less than 3% over the solar spectrum. The light-trapping properties of the structures were investigated through absorption measurements on thin wafers, and a nearly 90% average absorption was obtained for samples with a 50-μm thickness. The smoothing of the surface and lifetime of the chemical solutions has been systematically studied. As a result, control over the surface geometry and optical properties have been obtained with this new single-step etching approach. Passivation of the surface with SiO2 is also investigated to realize device implementation in the next step.

Effect of laser parameters and post-texturing treatments on the optical and electrical properties of laser textured c-Si wafers

Surface plays a crucial role in the performance of crystalline silicon (cSi) based solar cells as it affects both electrical and optical properties. To minimize reflection from the flat surface and thus improve light trapping, the cSi wafers must be textured. For mono-cSi cells, anisotropic alkaline etchants are commonly utilized to create pyramids on the surface. However, this method is not viable for multi-crystalline silicon (mc-Si) wafers due to the presence of different and random crystallographic orientations. In this work, we employed laser texturing, which is an isotropic texturing process, as an alternative texturing method for mc-Si wafers. This approach utilizes a laser process to create pits on the cSi surface. The laser’s processing parameters were justified by performing a series of experiments. After texturing, physical (ultrasonic bath with deionized water) and chemical (in KOH with two different concentrations of 1 and 20%) cleanings with different durations were performed which were esse...

Light management on industrial size c-Si solar cells by Si nanowires fabricated by metal-assisted etching

Absorption of the light by a solar cell can be improved significantly by light trapping structures formed on the front surface of the device. In particular, thin crystalline and amorphous solar cells are expected to benefit from the improved light absorption in a region closer to the surface of the cell. Recently, we have shown that vertically aligned silicon (Si) nanowires formed on flat (100) Si wafer surface by metal assisted etching can effectively be used for this purpose. In this paper we present demonstration of nanowire application to industrial size solar cell system and a comparison between flat and pyramid textured Si wafers. Standard procedures were followed to fabricate solar cells with and without Si nanowire process on mirror like and pyramid textured Si wafers. The dependence of the solar cell parameters on the process parameters was studied systematically. Reflection spectra showed successful light trapping behavior on the surface of the cells. In all samples, we have obtained excellent current-voltage (I-V) characteristics with high fill factors. However, the efficiency of the cells was found to decrease with the etch duration. This can be attributed to the increased recombination along the nanowires or increased surface area due to the roughening of the surface after etching process.