Hydrogenated amorphous silicon p–i–n solar cells deposited under well controlled ion bombardment using pulse‐shaped substrate biasing

We applied pulse‐shaped biasing (PSB) to the expanding thermal plasma deposition of intrinsic hydrogenated amorphous silicon layers at substrate temperatures of 200 °C and growth rates of about 1 nm/s. Fourier transform infrared spectroscopy of intrinsic films showed a densification with increasing deposited energy and a reduction in void content, whereas dual‐beam photoconductivity measurements showed an increase in Urbach energy above 4.8 eV/Si atom. From dark conductivity and photoconductivity measurements, we determined a maximum photoresponse of 2 × 106 at 3 eV/Si atom, which decreased at higher deposited energies because of a higher dark conductivity as a result of a lower band gap. p–i–n solar cells with PSB applied during the intrinsic layer deposition showed initial energy conversion efficiencies of 7.4% at around 1 eV/Si atom. Decreasing open‐circuit voltage at >1 eV/Si atom can be related to a lower band gap, whereas the short‐circuit current drops at >4.8 eV/Si atom, predominantly because of hole collection losses as determined from quantum efficiency measurements. The reduced fill factor for >1 eV/Si atom was presumably related to a decrease in mobility‐lifetime product because of an increase in defect density.