The impact of defects on the performance of p- and n-side illuminated microcrystalline silicon solar cells is investigated. The absorber layer spin density NS is controlled over some two orders of magnitude by electron bombardment and subsequent annealing steps. At increased NS (between 3x1016 and 1018 cm-3) performance of n-side illuminated cells is much more strongly reduced relative to p-side illuminated cells, particularly with regard to short circuit current density. Quantum efficiency measurements indicate a corresponding strong asymmetry in wavelength-dependence, which has been successfully reproduced by numerical device simulations. / Copyright (2012) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.
Appl. Phys. Lett. 101, 143903 (2012)

N-type hydrogenated microcrystalline silicon oxide (μc-SiOx:H) layers were used as window layers in n-side illuminated microcrystalline silicon n–i–p solar cells. Optical, electrical and structural properties of μc-SiOx:H films were investigated by Photothermal Deflection Spectroscopy, conductivity and Raman scattering measurements. μc-SiOx:H layers were prepared over a range of carbon dioxide (CO2) flow and film thickness, and the effects on the solar cell performance were investigated. By optimising the μc-SiOx:H window layer properties, an improved short-circuit current density of 23.4 mA/cm2 is achieved, leading to an efficiency of 8.0% for 1μm thick absorber layer and Ag back contact. The correlation between cell performance and μc-SiOx:H layer properties is discussed. The results are compared to the performance of solar cells prepared with alternative optimised window layers.
Phys. Status Solidi C 7,1053–1056 (2010)

A study of the effects of microcrystalline silicon i-layer modification near p/i interface in tandem configuration silicon thin film solar cells is presented. The structural properties of the absorber layers were investigated by Raman spectroscopy at different stages of growth. The results indicate the possibility of improving both the nucleation process and the film homogeneity in the direction of growth, without specific re-optimization of the p-layer, transferred from a single-junction microcrystalline silicon cell. Structural modifications of the i-layer have been correlated with performance of tandem solar cells, leading to improvements in the bottom cell current Jsc (up to 11.4 mA/cm2) and initial tandem-cell conversion efficiency (up to 11.3%).
Materials Science and Engineering B 159-160, p. 44-47 (2009)

The effects of exposure to atmosphere (ageing) and light-soaking on coplanar dark- and photo-conductivity of silicon films of varying crystallinity are examined. Dark conductivity generally increases on ageing in films with significant amorphous fraction and decreases in largely crystalline films, and may be reversed by annealing under vacuum at 130 °C consistent with adsorption and desorption of atmospheric components. Thinner films are more strongly affected by ageing. Boron doping appears to compensate charge introduced by ageing, though there are disagreements in detail. In comparison with ageing, moderate light-soaking affects dark conductivity in transitional microcrystalline silicon films only slightly. Both processes change the majority carrier mu–tau product in line with shifts in Fermi level position.
J. Non-Cryst. Solids 352, p. 1075 (2006)

Measurements of dark conductivity, steady-state and transient photoconductivity in undoped and boron-doped microcrystalline silicon films exposed to room air are reported. Two aging processes are identified: (i) an increase in dark conductivity and mobility-lifetime product occurring over several days, that may be reversed by heating to 160 °C under vacuum, and subsequently re-cycled, (ii) an irreversible change in the density of states occurring over a period of several months. It is proposed that the reversible effect is associated with charge transport in a region of electron accumulation induced by weakly-adsorbed water, whereas the irreversible effect, identified from its transient photocurrent signature, is associated with a true change in the density of states within the transport path, possibly as a result of slow chemical reactions at silicon grain boundaries.
J. Non-Cryst. Solids 338, p. 421 (2004)