Control of nanostructure of plasma CVD films for third generation photovoltaics

One of the requirements for successful application of hydrogenated amorphous silicon (a-Si:H) to promising tandem cells, that aim at high efficiency and low production cost, is to overcome its light induced degradation, which reduces significantly the initial conversion efficiency with light exposure. Our previous studies indicate a relation between light induced degradation and the incorporation of amorphous silicon nanoparticles (clusters) into a-Si:H films. Here we report control of nanostructure of a-Si:H films using a multi-hollow plasma CVD reactor. Deposition with low or non-incorporation of clusters is realized in the upstream region far from discharges in the reactor, whereas in the downstream region the volume fraction of clusters in films increases with the distance from discharge region. Films with a lower volume fraction tend to show better stability against light exposure.