All p-i-n hydrogenated amorphous silicon oxide thin film solar cells for semi-transparent solar cells

Highlights: •All p-i-n layer amorphous silicon oxide solar cells were made. •CO₂/SiH₄ ratio varied from 0 to 0.6 to find an effect of oxygen addition in absorber. •An Efficiency of semitransparent solar cell increased at CO₂/SiH₄ ratio of 0.2. •Transmission of solar cells was also improved with the oxygen addition. -- Abstract: We focused on fabricating all p-i-n layer hydrogenated amorphous silicon oxide (a-SiO_x:H) thin film solar cells in order to improve their transmittance in visible ranges of 500–800 nm for application in building integrated photovoltaics system. We varied CO₂/SiH₄ (R) gas flow ratio from 0 to 0.6 for i-layer to investigate an effect of oxygen addition. When the R ratio increased, the transmittance of devices improved due to the enhancement in optical bandgap of the absorber. However, power conversion efficiency (PCE) decreased owing to the increase in defects and recombination rate which might be ascribed to back bonding of oxygen atoms with Si atoms. Unlike other R flow ratio, however, the PCE of a-SiO_x:H solar cell at the R ratio of 0.2 was slightly improved by the increase in open circuit voltage as indicated by the wide band gap and the increase in quantum efficiency within short-wavelengths (300–500 nm). We introduced a figure of merit (FOM), multiplication of PCE and average transmittance in range of 500–800 nm, in order to assess the performance of transparent solar cells. The a-SiO_x:H solar cell at the R ratio of 0.2 achieved the highest FOM, which was better than conventional amorphous silicon solar cell.