Light Induced Defect Creation Kinetics in Thin Film Protocrystalline Silicon Materials and Their Solar Cells

Abstract

Using real time spectroscopic ellipsometry to characterize the microstructure and evolutionary growth of Si:H materials deposited with and without hydrogen dilution, phase diagrams were developed which clearly defined and established growth in the protocrystalline regime. Guided by these phase diagrams thin films and intrinsic layers in p-i-n cell structures were grown which consist solely of the protocrystalline phase so that the bulk uniform properties of the material could be characterized with confidence. Studies were carried out on the light induced changes in these films and cell structures that include the annealing out of defects as well as their creation under 1 sun illumination at temperatures from 25°C to 100°C that include the attainment of a degraded steady states (DSS). Defect states were characterized in films with electron mobility lifetimes (μτ), and subgap absorption at 1.2eV (α(1.2)); and in the i material of the p-i-n cells by the bulk limited fill factor (FF). The contributions of the different gap states to SWE are identified and characterized. The absence of direct correlations between α(1.2) with μτ and FF present in undiluted and diluted materials also found in protocrystalline Si:H. Similarities, on the other hand, are found between the μτ products and the FFs including the striking changes in the kinetics that occur at ∼40°C. Direct correlations between the changes in μτ and FF at different temperatures are presented. The reason for this correlation and lack of it for α(1.2) are briefly discussed with direct correlation of the α(1.2) to cell characteristics being presented, be it not with the FF.

Relationship between defect density and charge carrier transport in amorphous and microcrystalline silicon

“…5,[9][10][11][12][13][14][15] Between a-Si: H and c-Si: H-the latter of course already being a class of materials instead of one well-defined material modification-there is an additional form of thinfilm silicon prepared in plasma-enhanced chemical vapor deposition ͑PECVD͒ processes with high hydrogen dilution close to the transition to microcrystalline growth. Such material called polymorph, paracrystalline, protocrystalline, or edge material [16][17][18][19][20] is reported to have reduced defect density, improved stability, and possible medium range order ͑MRO͒. [21][22][23][24][25][26] Such material is since long used as absorber layer in solar cells, in particular, in the top cells of stacked devices.…”

The enhancement of nanocrystallization in amorphous silicon thin films deposited on glass substrate

“…In fact, it has been known that crystallites formed in amorphous silicon have different physical profiles depending on the thickness [6]. We look into two identical amorphous silicon thin films but different ones in thickness with the measurements of XTEM, Raman scattering, and XRD.…”

Amorphous silicon solar cells deposited with non-constant silane concentration

“…Several explanations for the increased stability of this type of thin-film silicon -sometimes referred to as protocrystalline, polymorphous, paracrystalline or edge material [7][8][9] -have been proposed. It is reported that these types of material features increased the medium range order in the silicon network, which led to reduced creation of light induced defects [10][11][12][13].…”