Improving the stability of amorphous silicon solar cells by chemical annealing

Amorphous silicon solar cells have been extensively studied. However, it is found that the properties of a-Si:H solar cells degrade upon light illumination, and this limits their application. Recently, it has been shown that this instability is correlated with the presence of SiH2 bonds, and a technique, namely chemical annealing, was suggested to improve the stability of a-Si:H. Although a number of results have been reported, no chemical annealed devices with good quality were reported;In this work, chemical annealing technique was studied to improve the stability of a-Si:H solar cells. It is found that when the annealing was done in hydrogen plasma, the films remained amorphous; in contrast, when in helium plasma, and the annealing time is equal or more than 20 seconds, the films became crystalline. These unusual results show that it is not necessary to have a high hydrogen dilution to obtain nanocrystalline films, and contradict the generally accepted assumption that high hydrogen dilutions are needed to crystallize the amorphous films based on the reactive etching of H ions. Instead, it might be the case that not only the reactive etching effect from the H ions, but also the ion bombardment play a role in crystallizing the amorphous films