Magnetron Sputtered Hydrogenated Silicon Thin Films: Assessment for Application in Photovoltaics

n-i-p Nanocrystalline Hydrogenated Silicon Solar Cells with RF-Magnetron Sputtered Absorbers

“…The devices fabricated with nc-Si:H i -layers at p H2 = 90% are found to result in the best performance. The optical response for the nc-Si:H film prepared at p H2 = 90% had the highest amplitude features in spectra in ε indicating the highest optical density among the nc-Si:H films prepared at p H2 = 80, 85, and 90% [9,10]. The n-i-p devices incorporating PECVD nc-Si:H i -layers prepared at R = 125, which is the minimum value of R required for immediate nanocrystalline growth for the i -layers deposited on the top of n -type PECVD nc-Si:H, have better device performance.…”

“…The optical response of the 0.9 µm of the PECVD i -layers adjacent to the p -layers is described by those of crystal silicon [28], and the 0.9 µm adjacent to the n -layers is described by a Bruggeman effective medium approximation [27] of 0.9 volume fraction crystal silicon and 0.1 volume fraction 1.8 eV band gap a-Si:H [29]. This bilayer approach provides a simplified model for Si:H growth evolution with increasing crystallinity as a function of accumulated film thickness [4,7,8,9,10,44]. The thinner 1 µm thick sputtered i -layer is described as a bilayer of the same material properties although the crystal silicon component of the i -layer adjacent to the p -layer is 0.1 µm thick, while the effective medium approximation of crystalline silicon and a-Si:H near the n -layer remains the same thickness and volume fraction as for the PECVD i -layers.…”

“…Sputtering is performed at 10 mTorr gas pressure with a constant hydrogen-to-argon gas flow ratio, p H2 = 100% × [H 2 ]/{[H 2 ] + [Ar]} in upstream mode for each deposition. Previous work [9,10] has successfully optimized these deposition conditions to produce reasonable growth rate material with controllable microstructure as identified by RTSE. Microstructure during sputtering is controlled by p H2 and typical growth rates are approximately 1.3 Å/s.…”

“…Among these two thin film absorbers, a-Si:H is vulnerable to the Staebler–Wronski effect [1] resulting in degradation under illumination, whereas nc-Si:H suffers from less or no light induced degradation. Several techniques are available for the fabrication of Si:H thin films including plasma enhanced chemical vapor deposition (PECVD: RF and VHF) [2,3,4,5,6,7,8], RF magnetron sputtering [9,10,11,12,13], hot-wire chemical vapor deposition [14,15,16], and other technologies [17,18]. Among these techniques, Si:H PV devices with PECVD absorbers are the most widely studied [2,3,4,5,6,7,8], but require toxic silicon carrying precursor gases (SiH 4 , Si 2 H 6 ).…”