High potential of thin (<1 µm) a‐Si: H/µc‐Si:H tandem solar cells

Abstract

Silicon based thin tandem solar cells were fabricated by plasma enhanced chemical vapor deposition (PECVD) in a 30 × 30 cm2 reactor. The layer thicknesses of the amorphous top cells and the microcrystalline bottom cells were significantly reduced compared to standard tandem cells that are optimized for high efficiency (typically with a total absorber layer thickness from 1.5 to 3 µm). The individual absorber layer thicknesses of the top and bottom cells were chosen so that the generated current densities are similar to each other. With such thin cells, having a total absorber layer thickness varying from 0.5 to 1.5 µm, initial efficiencies of 8.6–10.7% were achieved. The effects of thickness variations of both absorber layers on the device properties have been separately investigated. With the help of quantum efficiency (QE) measurements, we could demonstrate that by reducing the bottom cell thickness the top cell current density increased which is addressed to back‐reflected light. Due to a very thin a‐Si:H top cell, the thin tandem cells show a much lower degradation rate under continuous illumination at open circuit conditions compared to standard tandem and a‐Si:H single junction cells. We demonstrate that thin tandem cells of around 550 nm show better stabilized efficiencies than a‐Si:H and µc‐Si:H single junction cells of comparable thickness. The results show the high potential of thin a‐Si/µc‐Si tandem cells for cost‐effective photovoltaics. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Resonances and absorption enhancement in thin film silicon solar cells with periodic interface texture

“…34 Keeping in mind the small differences in refractive index between amorphous and microcrystalline silicon, the results shown in Fig. 10 are very close to the properties of the latter cell type, and the higher number of resonances in the thicker absorber layer makes the statistical treatment more justified.…”

Hydrogenated amorphous silicon oxide containing a microcrystalline silicon phase and usage as an intermediate reflector in thin-film silicon solar cells

“…To estimate the influence of the intermediate reflector on the FF we added numerically an Ohmic IV-characteristic of a series resistance R s corresponding to the resistance of the intermediate reflector to a measured IV-characteristic of our standard tandem solar cell. For an additional series resistance of 1 X cm 2 we calculated a decrease in FF of about 1%. When increasing this series resistance to 10 X cm 2 we expect a drop in FF of about 7%.…”

“…For an additional series resistance of 1 X cm 2 we calculated a decrease in FF of about 1%. When increasing this series resistance to 10 X cm 2 we expect a drop in FF of about 7%. A similar dependency between R s and FF was also found in.…”

Hydrogenated microcrystalline silicon germanium as bottom sub-cell absorber for triple junction solar cell

“…As shown in Table 1, with increasing D bottom , V oc decreases from 2.02 V of the thinnest 800 nm to 1.89 V of 2000 nm. The decrease is mainly attributed to the narrower splitting of the quasi-Fermi levels due to the larger recombination volume [17]. For the triple junction solar cells prepared in this study, the bottom sub-cell has the lowest FF, while the top sub-cell has the highest FF.…”

“…Moreover, the spectral response of the middle sub-cells in the wavelength region of 700-900 nm is reduced with increasing D bottom . This reduction is due to the decreased absorption of the light reflected by the ZnO/Ag back reflector [13,17].…”