High-efficiency µc-Si solar cells made by very high-frequency plasma-enhanced chemical vapor deposition

Abstract

Microcrystalline silicon‐based single‐junction p–i–n solar cells have been fabricated by very high‐frequency plasma enhanced chemical vapor deposition using a showerhead cathode at high pressures and under silane depletion conditions. The i‐layers are made near the transition from amorphous to crystalline. It was found that, especially at high crystalline fractions, the open‐circuit voltage and fill factor are very sensitive to the morphology of the substrate. At an i‐layer deposition rate 0·45 nm/s, we have measured a stabilised efficiency of 10% (Voc = 0·52 V, FF = 0·74) for a cell made on texture‐etched ZnO:Al. The performance is stable under light soaking. The defect density of the absorber layer is in the 1015 cm−3 range. In spite of the presence of oxygen contamination, good electrical properties and good infrared cell response are obtained. Copyright © 2006 John Wiley & Sons, Ltd.

Controlling the quality of nanocrystalline silicon made by hot-wire chemical vapor deposition by using a reverse H2 profiling technique

“…In PECVD, R H is decreased during i-layer deposition [15] to suppress the development of the deposited nc-Si:H i-layers toward higher crystallinity. Using this technique, a general increase in all the cell parameters was observed, thus improving the solar cell efficiency considerably [15,16]. In our case, since the i-layer structure develops in the opposite direction, we used a reverse H 2 profiling scheme, namely an increase of the R H while depositing the i-layer, instead of decreasing it.…”

Nanocystalline silicon solar cells

“…At constant hydrogen dilution, due to conical growth of grain columns, there is a quadratic increase of the crystallinity with an increase of thickness. By employing a parabolic type of grading where the hydrogen dilution is reduced step wise to maintain the crystallinity at a constant level, a more homogeneous growth of the i-layer can be made, as confirmed by comparing the Raman spectra obtained from the top (n) and bottom (p) side of the nanocrystalline silicon cell [29]. The efficiencies of the p-i-n nc-Si solar cells with and without parabolic grading are shown in Fig.…”

“…It has been observed that the crystalline component is a major deciding factor for the photosensitivity of the material. The best cell performance is obtained at R c of ∼0.4 [29]. Therefore, this quantity is meticulously maintained in the material when comparing the behaviour of solar cells with i-layers made at different deposition conditions.…”

Microcrystalline silicon solar cells with an open-circuit voltage above 600mV

“…[7][8][9][10][11] However, in 2002 a best-cell V oc of 580 mV was reported for c-Si: H solar cells prepared by hot wire deposition. 12 For very high frequency ͑VHF͒ plasma-deposited solar cells a best-cell V oc around 570 mV was reported in 2005 by the application of a hot wire ͑HW͒ deposited buffer layer between the p and i layers.…”