Metastability studies in silicon thin films: from short range ordered to medium and long range ordered materials

Limiting factors in the fabrication of microcrystalline silicon solar cells and microcrystalline/amorphous (‘micromorph’) tandems

“…However, the i-layers had a high crystalline fraction. Complementary studies have demonstrated that with i-layers of medium crystallinity (40-60%), single-junction solar cells suffer from a mild form of lightinduced degradation when exposed to blue or white light [73][74][75][76][77]. The light-induced degradation is larger for blue light (for constant short-circuit current density) due to a larger absorption in the amorphous phase and at the p-i interface, as discussed by Yan et al [77], who additionally observed that mc-Si:H solar cells are fully stable when exposed to red light only.…”

Towards 12% stabilised efficiency in single junction polymorphous silicon solar cells: experimental developments and model predictions

“…Pm-Si:H is a nano-structured silicon material with medium range order which shows up in the superior hole transport properties as deduced from diffusion induced time resolved microwave conductivity [8] and time-of-flight measurements [9]. Moreover it exhibits lower initial [5] and stabilised defect densities than standard a-Si:H [1,9,10], with the ημτ product of electrons 200-700 times higher than that of standard a-Si:H for samples in the as-deposited state [1], and attaining values after light-soaking comparable to those of standard a-Si:H films before degradation [1,[4][5][6][7]. In reference [1], a comparative study has been made of the kinetics of defect creation in • C and 210 • C; (c) and (d) of the various P-layers studied: P-μc-Si:H, P-a-SiC:H and P-μc-SiOx:H; and (e) and (f) of the different N-layers: N-a-Si:H, N-μc-SiOx:H and the TCO: ZnO:Al.…”

“…To this end, we have been experimenting with an a-Si:H-like material: hydrogenated polymorphous silicon (pm-Si:H), which is produced by the standard RF glow discharge decomposition of silane highly diluted in hydrogen, under conditions close to powder formation [4][5][6][7][8]. Pm-Si:H is a nano-structured silicon material with medium range order which shows up in the superior hole transport properties as deduced from diffusion induced time resolved microwave conductivity [8] and time-of-flight measurements [9].…”

“…This is likely due to the superior nature and/or light absorption of the a-Si:H material developed, improved P/I interface properties in their deposited solar cells, etc. On the other hand we have been able to develop pm-Si:H [1,[4][5][6][7][8], a close cousin of a-Si:H, with lower initial and stabilised defect densities, higher hole mobility, but lower light absorption. Using modelling we show in this article that such a material when deposited in a solar cell in the NIP configuration, and in conjunction with suitable P-and N-layers and an ARC is capable of attaining a stabilised efficiency of around 12%, although our best experimental results so far show a lower stabilised efficiency [19].…”

Molecular hydrogen diffusion in nanostructured amorphous silicon thin films

“…2,3 In contrast, polymorphous silicon ͑pm-Si:H͒, a grade of nanostructured amorphous silicon, exhibits enhanced hole mobility 4 and a lower density of metastable electronic defects after prolonged illumination. 5,6 Despite the importance of H stability and evolution in a-Si:H and pm-Si:H, there is still a lot we do not know about it.…”