Abstract
The determination of optical parameters, such as absorption and extinction coefficients, refractive index and the bandgap energy, is crucial to understand the behavior and final efficiency of thin film solar cells based on hydrogenated amorphous silicon (a-Si:H). The influence of small variations of the gas flow rates used for the preparation of the p-a-SiC:H layer on the bandgap energy, as well as on the dopant elements concentration, thickness and conductivity of the p-layer, is investigated in this work using several complementary techniques. UV-NIR spectrophotometry and ellipsometry were used for the determination of bandgap energies of four p-a-SiC:H thin films, prepared by using different B2H6 and SiH4 fluxes (B2H6 from 12 sccm to 20 sccm and SiH4 from 6 sccm to 10 sccm). Moreover, radiofrequency glow discharge optical emission spectrometry technique was used for depth profiling characterization of p-a-SiC:H thin films and valuable information about dopant elements concentration and distribution throughout the coating was found. Finally, a direct relationship between the conductivity of p-a-SiC:H thin films and the dopant elements concentration, particularly boron and carbon, was observed for the four selected samples.
Highlights
Nowadays, an interesting approach of photovoltaic (PV) devices is based on the possibility to grow silicon in the form of a thin film onto a given substrate [1]
Similar bandgap energies were obtained for the four p-layers with the gas flow rates investigated by UV-NIR spectrophotometry and ellipsometry, significant differences were observed in the qualitative depth profiles obtained by rf-glow discharge coupled with optical emission spectrometry (GD-OES)
Four p-layers, amorphous silicon (a-Si):H thin films doped with B and C, containing different dopant elements concentration prepared by varying the gas flow rates during the preparation stage were grown on two different substrates: highly resistive glasses and mirror-polished zinc
Summary
An interesting approach of photovoltaic (PV) devices is based on the possibility to grow silicon in the form of a thin film (nanometer thickness) onto a given substrate [1]. The use of direct solid analysis spectrometric techniques [15,16] may offer great interest for the characterization of TFSCs, because they provide elemental information of major and trace constituents of great value to better understand the processes occurring at nanometer length dimensions (e.g., distribution and concentration of doping elements through the solar cell films, possible diffusion processes, presence of impurities and thickness of the layers) that have a direct influence on the bandgap energy and, on the final efficiency of PV devices for energy production In this context, glow discharge coupled with optical emission spectrometry (GD-OES). The possible relationship between the conductivity of the p-a-SiC:H thin film and the concentration of dopant elements, boron and carbon, was investigated for the four selected samples
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