Rough ZnO layers by LP-CVD process and their effect in improving performances of amorphous and microcrystalline silicon solar cells

Abstract

Doped ZnO layers deposited by low-pressure chemical vapour deposition technique have been studied for their use as transparent contact layers for thin-film silicon solar cells.Surface roughness of these ZnO layers is related to their light-scattering capability; this is shown to be of prime importance to enhance the current generation in thin-film silicon solar cells. Surface roughness has been tuned over a large range of values, by varying thickness and/or doping concentration of the ZnO layers.A method is proposed to optimize the light-scattering capacity of ZnO layers, and the incorporation of these layers as front transparent conductive oxides for p-i-n thin-film microcrystalline silicon solar cells is studied.

Microcrystalline silicon solar cells: effect of substrate temperature on cracks and their role in post‐oxidation

“…In our laboratory, mc-Si:H p-i-n solar cells are deposited on glass covered by low pressure chemical vapor deposition zinc oxide (LPCVD ZnO), which possesses a natural texture, with as-grown pyramids at the surface, exhibiting typically a V-shape structure [19,20]. Depending on the transparent conductive oxide (TCO) growth process conditions and on the ''sharpness'' of the V-shapes, such as TCO surface morphology, can lead to severe degradation of the performances of mc-Si:H solar cells, as those are particularly sensitive to cracks that appear in the intrinsic layer because of the V-shape.…”

The role of front and back electrodes in parasitic absorption in thin-film solar cells

“…In order to keep the same morphology for both types of front electrodes, a stack of two layers is used in the n-i-d case. A 7-µm-thick layer is first deposited on glass and flattened by chemo-mechanical polishing (CMP) to erase the very large pyramidal features that naturally form on its surface during layer growth [22]. This polishing is made by immersing the sample in a diluted suspension of silica nanoparticles as typically used for CMP, and scanning the surface with a felt-covered drill-head.…”

“…To inhibit epitaxial growth on this polished surface, an ultra-thin (<3 nm) n-doped µc-Si:H layer is subsequently deposited; a n-i-d ZnO film is then deposited on top, with thickness adjusted to match the surface morphology of the 2-µm-thick doped layer. Due to a reduction of the lateral growth rate of the grains when LPCVD ZnO is doped [22], this rough n-i-d layer is only 1.6-µm-thick.…”

Enhanced mobility of hydrogenated MO-LPCVD ZnO contacts for high performances thin film silicon solar cells

“…In fact, the Std layer suffers from strong parasitic light absorption (FCA) due to the high doping level. In addition, the high doping produces in the ZnO smaller grains than in the n-i-d, which decreases the light scattering at the ZnO-Si interface [12].Also, it can be seen that the cell deposited on the n-i-d_pH2 electrode generates slightly more current in the blue part of the spectrum than on the n-i-d non-treated ZnO, thanks to the widening of its band gap, as discussed in previous section. Actually, this approach should be especially advantageous in the case of tandem amorphous/ microcrystalline μc-Si:H (micromorph) TF Si solar cells, where the current generation in the bottom μc-Si:H cell is crucial [13].…”