Development of p-type nano crystalline Si film for electrical contact layer with the front electrode of amorphous silicon oxide type solar cell

In a thin film solar cell the doped p-type and n-type layers provide electric field that helps to separate the photo generated electron-hole pairs from the active layer. In order to achieve a better electrical transport of holes from the p-layer to the transparent conducting oxide electrode (TCO), the TCO/p interface was improved. We used a p-type double layer, consisting of high conductivity p-type nano crystalline silicon (p-nc-Si:H) and wide band gap hydrogenated amorphous silicon oxide (p-a-SiO:H), where the TCO/p-nc-Si:H was expected to give better electrical contact. As a result, an improved cell characteristics was observed with efficiency of 6.25%, with 900 mV open circuit voltage, 11 mA/cm² short circuit current density, 63.3% fill factor. The optimized p-nc-Si:H layer had electrical conductivity of 1.1 S/cm, activation energy of 41 meV and optical energy band gap of 2.04 eV, that was prepared in a radio frequency plasma enhanced chemical vapor deposition with high hydrogen dilution. One of the primary reasons for such an improvement is thought to be an improved electronic band structure at the TCO/p interface and efficient hole collection.