Process control of high rate microcrystalline silicon based solar cell deposition by optical emission spectroscopy

Silicon thin-film solar cells based on microcrystalline silicon (c-Si:H) were prepared in a 30 × 30 cm2 plasma-enhanced chemical vapor deposition reactor using 13.56 or 40.68 MHz plasma excitation frequency. Plasma emission was recorded by optical emission spectroscopy during c-Si:H absorber layer deposition at deposition rates between 0.5 and 2.5 nm/s. The time course of SiH* and H emission indicated strong drifts in the process conditions particularly at low total gas flows. By actively controlling the SiH4 gas flow, the observed process drifts were successfully suppressed resulting in a more homogeneous i-layer crystallinity along the growth direction. In a deposition regime with efficient usage of the process gas, the c-Si:H solar cell efficiency was enhanced from 7.9 % up to 8.8 % by applying process control.