Relation between substrate surface morphology and microcrystalline silicon solar cell performance

Abstract

In the present paper, the structural and electrical performances of microcrystalline silicon (lc-Si:H) single junction solar cells codeposited on a series of substrates having different surface morphologies varying from V-shaped to U-shaped valleys, are analyzed. Transmission electron microscopy (TEM) is used to quantify the density of cracks within the cells deposited on the various substrates. Standard 1 sun, variable illumination measurements (VIM) and Dark J(V) measurements are performed to evaluate the electrical performances of the devices. A marked increase of the reverse saturation current density (J 0 ) is observed for increasing crack densities. By introducing a novel equivalent circuit taking into account such cracks as non-linear shunts, the authors are able to relate the magnitude of the decrease of V oc and FF to the increasing density of cracks.

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

“…The improvement of FF between 170 and 2308C can then be attributed, as expected, to the decrease of cracks density (already seen in Ref. [15]). Indeed, this latter is reduced by 50% for slightly surface treated ZnO (black squares on Figure 3a) and by 87% for strongly surface treated ZnO (red circles on Figure 3a) when the temperature is raised from 170 to 2708C.…”

“…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. As already demonstrated in previous works [15,16], these cracks have mainly detrimental effects on the fill factor (FF) and open-circuit voltage (V oc ), and act as bad diodes with a high reverse saturation current. In Ref.…”

“…Indeed, zone of cracks are clearly pointed out to be responsible for bad electrical performances [15], and this less-dense material permits the incorporation of oxygen after the deposition of the silicon layers (postoxidation). To increase the density of mc-Si:H material, one way is to modify the substrate morphology from Vshape to U-shape, but this will influence the scattering of the light, and hence, the short-circuit current density of the solar cells.…”

“…Although ''cracks'' have been reported in the past by several authors [11][12][13][14], their full role in limiting the device performance has only been evidenced recently [15][16][17][18]. 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].…”

Nanoimprint Lithography for High-Efficiency Thin-Film Silicon Solar Cells

“…41 This could explain the discrepancy between the estimated 17% and the observed 12% improvement in FF when going from single to tandem junction. A detailed statistical analysis of the crack distribution 47 is out of the scope of the present work. However, new approaches to reduce the number of cracks and to limit their negative impact on the V oc and FF of the cells are currently being intensively investigated in our lab.…”