Elimination of hydrogenation-induced contact degradation of evaporated poly-Si thin-film solar cells on glass

Severe Al/poly-Si contact degradation is observed after metallising p-type BSF (back surface field) layers of poly-Si thin-film diodes on glass which received a hydrogen passivation treatment prior to contact formation. The degradation is confirmed by comparative dark I-V measurements on the hydrogenated and non-hydrogenated samples. Two methods - thermal annealing and Si etching using coloured HF - are employed to address this problem induced by hydrogenation processing. Both methods improve the contact properties between p-type poly Si and evaporated Al significantly and lead to good ohmic contacts with low specific contact resistance. In contrast, it is found that contacts between Al and n-type BSF layers do not degrade after hydrogenation but when the sample is treated by either of the above methods. The possible reasons are discussed.